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EOS User`s Guide, Release 2

1. Disk space allocation in EOS is based on the binary buddy system A storage area is organized as a number of fixed size extents or buddy spaces disk sections of physically adjacent pages Segments are variable size sequences of physically adjacent disk pages taken from one of the buddy spaces There is a 1 block allocation map directory associated with each extent indicating the status free or allocated and the size of each segment in the extent With 4k byte disk blocks the maximum extent size is approximately 63 5 megabytes Bil92a To maximize performance the extent size may have to be carefully matched to the physical properties of the disk device 2 1 2 Object Identifiers OIDs EOS objects are stored on slotted pages and they are identified by system generated object ids oids The object id is an 8 byte quantity it is the physical address in which the object is stored in the database and it consists of the following the storage area number and the page number within the area the object is stored in the slot number that gives the offset of the object within the page and a number to approximate unique ids when space is re used 2 1 3 Named Objects Any EOS object can be given a name An object may have at most one name and a name may correspond to at most one object EOS guarantees that the referential integrity between named objects and their corresponding names is enforced e g when a named object is removed from a database
2. include lt stdio h gt include lt stdlib h gt include Part h define ErrR msg printf msg return 1 int create_parts eosdatabase db eos_Ref lt eos_Ref lt Part gt gt pers_array Part a_part 44 Create the array of pointers to parts and give it a name pers_array new db eos_Ref lt Part gt NPARTS if pers_array is_null ErrR Failed to create the persistent array of references to Parts if db gt set_object_name pers_array part_array ErrR Cannot set the name to 4s part_array Create the part objects and store references to them in the pers_array for int i 0 i lt NPARTS i pers_array i new db Part if pers_array i is_null ErrR Failed to create a persistent Part a_part pers_array i a_part gt name new db char NAME_SIZE if a_part gt name is_null ErrR Failed to create the persistent name of a Part sprintf char a_part gt name Part Object With Number d i a_part gt part_no i Link the object together for int j 0 j lt NPARTS j a_part pers_array j a_part gt x_part pers_array rand NPARTS a_part gt y_part pers_array rand NPARTS a_part gt z_part pers_array rand NPARTS return 0 FILLILELLLTTTT LTT LTS T TT main int argc char argv eosdatabase db if argc 2 printf Usage 4s database_name n argv 0 exit 1 45 if
3. int flags 0 int ano 0 creates a new file The new file is a child of the file pfile and it is created in area ano if the value passed is different than 0 Otherwise it is created in the same area as the pfile The new file is unnamed unless name points to a string in which case the file gets this name Applications that 22 want to associate names with files may first create an unnamed file and then give a name to it The parameter flags is used as in the eosobj create function static eosfile create eosdatabase db const char name 0 int flags 0 int ano 0 creates a new file as a child of the root file of the database db static eosfile open const eosoid amp oid opens the file with id oid It returns the file descriptor or zero on failure static eosfile open const eosdatabase db const char name opens the file with name name in the database db It returns the file descriptor or zero on failure static eosfile of const eosobj obj returns the file descriptor of the file containing the object obj int destroy void removes the file and all the objects it contains An attempt to remove a root file will result in error the root file of a database is removed when the database itself is removed It returns zero on success non zero on failure int clear void removes all the objects belonging to the file without removing the file itself It returns zero on success non zero on failure int npages void const ret
4. and it returns either an integer 4 0 or NULL depending on its interface eosexten CONTINUE The user function func successfully completed its operations The flow of the EOS function that called func remains unchanged eosexten RETURN The user function func successfully completed its operations The EOS function that called func skips the remaining steps and returns success immediately This is translated to a returned value of 0 when the EOS function returns an integer and the value of that member of the eosstat structure used by the registered function that has the same type as the EOS function prototype 5 13 3 Argument Passed to User Functions The eosstat structure has the following members typedef struct eosstat eosdatabase db unsigned create 1 unsigned trunc 1 unsigned rdonly 1 unsigned normal 1 char name eosobj obj eosfile file eosfile pfile eosoid oid int flags int hint int size eosstat 5 13 4 Primitive Events When a primitive event is trapped members of the eosstat structure are initialized The events that EOS traps and the members of the eosstat set for each event are described below The members of the eosstat structure are set from the values of the corresponding arguments of the EOS function that called the registered function 30 TR_BEGIN TR_COMMIT TR_ABORT TR_DEADLOCK DB_OPEN DB_REMOVE FILE_CREATE FILE_OPEN FILE_REMOVE OBJECT _FAULT C
5. anyL eos_Ref lt T gt amp refR friend int operator const eos_Ref lt T gt amp refL const eos_Ref lt T gt amp refR friend int operator const eos_Ref lt T gt amp refL const T ptrR friend int operator const T ptrL eos_Ref lt T gt amp refR friend int operator const eos_Ref lt T gt amp refL const eos_Ref_Any amp anyR friend int operator const eos_Ref_Any amp anyL eos_Ref lt T gt amp refR these operators are used for testing for equality and inequality 5 4 Databases class eosdatabase The following functions create open remove and truncate a database A database may be opened many times it will be closed when an equal number of database close function invocations are performed In addition a number of databases belonging to the same or different areas can be open at any point in time static eosdatabase open const char name int rdonly 0 int create 0 int trunc 0 opens the database specified in name The name argument must have the following format hostname areaname dbname If hostname is omitted it s value is taken from the clientrc configuration file Note that the areaname must be a rooted path relative to the server not the client The remaining of the arguments are used in the following way 16 rdonly if true the database is opened for reading only create if true the database will be created if it does not exist trunc if true the contents of the database will be purged For
6. applies only to storage areas that are UNIX files EOS_AREA_HOST_NAME The default host machine name the area manager is running on EOS_AREA_HOST_PORT The port number used for communication with the area manager It must be different than the EOS_SERVER_HOST_PORT number in the clientrc file 7 2 Customizing the Client clientrc The following are the environment variables for the client program EOS_POOL SIZE The maximum size of the transaction s buffer pool measured in pages 4K bytes each The cache is created incrementally in chunks of EOS POOL_INCREMENTS pages The maximum size of the client cache affects the performance of the client program A small cache will force the EOS client cache manager to force pages out of the cache sooner than a larger cache On the other hand a very large cache will increase the operating system s swapping activity due to memory size limitations and activities from other users running on the same client machine It s hard to come up with a right size for all applications a user may tun As a general suggestion keep this number large e g 16 or 32 megabytes and then experiment with the EOS_POOL_INCREMENTS value EOS_POOL_INCREMENTS The number of frames allocated to the transaction s cache each time more frames are needed until the cache has reached its final size EOS_LO_SEG_THRESHOLD It affects large objects only It specifies the default segment size threshold used when updates a
7. be visited If the eosfilescan AUTO_FWRD order was specified the cursor will be positioned to the next object If the eosfilescan AUTO_BWRD order was specified the cursor will be positioned on the previous object By specifying the eosfilescan MANUAL the cursor will remain unchanged int eosfilescan close closes a file scan When the eosfilescan MANUAL order is specified the cursor must be moved explicitly by using the following functions They all return zero on success non zero on failure Note that it is NOT an error to seek to the first next previous or last object when no such object exists in the file or the page depending on the kind of scan In this case a call to cursor will simply return eosoid null int first int inpage 0 positions the cursor to the first object within the current page if the value of inpage is true or within the file if its value is false int last int inpage 0 positions the cursor to the last object within the current page if the value of inpage is true or within the file if its value is false int next int inpage 0 positions the cursor to the next object within the current page if the value of inpage is true or within the file if its value is false int prev int inpage 0 positions the cursor to the previous object within the current page if the value of inpage is true or within the file if its value is false int seek_at const eosoid amp oid positions the cursor on th
8. clients interested in establishing a con nection One way of achieving this is by having an entry in the etc services file If this is not possible then try to use a port number between 1024 and 5000 for the Internet EOS_REPORT_PROGRESS If its value is not 0 then most of the steps followed in each operation carried out by the server will be displayed on the screen If the value is 0 only error conditions are reported EOS_LOCK_IS_ENABLED If its value is not 0 then the concurrency control module will be active and locks are acquired while accessing the database Otherwise no locks are placed of the pages accessed The default value is 1 NOTE no guarantee is given that the system will operate in a consistent and correct way when the lock manager is turned off EOS_LOG_IS_ENABLED If its value is not 0 then all the updates performed by committed transactions will be logged on durable storage If the value is 0 no logging is performed NOTE no guarantee is given that the system will be in a consistent state should a failure occur and the log manager is off EOS_AUTO_RESTART If its value is not 0 when the server starts it makes sure that all updates performed by all committed transactions in the past are in the database If the value is 0 the servers does not check wether the database is consistent NOTE no guarantee is given that the system will behave correctly in the case where a failure occurred and the automatic restart is tu
9. db eosdatabase open argv 1 0 1 NULL printf Cannot create database s n argv 1 exit 2 if eostrans begin 0 printf Cannot start a transaction n exit 3 if create_parts db printf Cannot create the objects n eostrans abort exit 1 if eostrans commit printf Transaction commit failed n eostrans abort exit 5 if db gt close printf Cannot close the opened database n exit 6 exit 0 9 3 File part_traverse c Usage traverse lt database name gt lt level of traversal gt This program starts from a random object and traverses the object hierarchy down to the level given in the input include lt stdio h gt include lt stdlib h gt include Part h The depth first traversal of the object hierarchy void traverse Part p int level if level 0 printf n return printf Part 4d with name s n p gt part_no char p gt name printf tVisiting x_part traverse p gt x_part level 1 printf tVisiting y_part traverse p gt y_part level 1 printf tVisiting z_part traverse p gt z_part level 1 return FILLLITTLTTLLLTLTTATS TTT LT TTT main int argc char argv eosdatabase db eos_Ref lt eos_Ref lt Part gt gt p_array 46 if argc 3 printf Usage 4s database level n argv 0 exit 1 if db eosdatabase open argv 1 NULL printf Canno
10. example the following piece of code opens the database phones in area usr alex areal on machine allegra if it exists eosdatabase db eosdatabase open allegra usr alex areail phones static eosdatabase of const eosobj obj returns the database descriptor of the database that contains the object obj or null on failure int open int rdonly 0 opens the database whose descriptor that has been retrieved by using one of the static functions eosdatabase open or eosdatabase of A non zero value argument opens the database with read only access It returns zero on success non zero on failure int close void closes the database It returns zero on success non zero on failure int destroy removes this database It returns zero on success non zero on failure int rename const char new_name changes the name of the database to newmname provided no other database in the same area has name new_name It returns zero on success non zero on failure int is_readonly void const returns true if the database has been opened for read only access const char name void returns the name of the database const eosoid amp rootoid void const returns the object id of the root file eosoid oid_of const char name returns the oid of the object whose name is name If no such object exists in this database the function returns eosoid null int set_object_name const eos_Ref_Any amp objRef const char name sets the name of
11. kernel The default value is 17K EOS_TR_FAIL_TIMEOUT The maximum allowable idle period for an application process ex pressed in minutes If the application does not have any interaction with the server during the above time period then the server unconditionally aborts the transaction 42 8 EOS File System Viewer eosfsview eosfsview is a primitive and not yet complete interactive browser that shows information about an EOS storage area databases files and objects The program accepts one argument the name of the area to be viewed When you run eosfsview you see this menu EOS Release x y z Options O quit 1 area info 2 list databases 4 make db 5 open db 6 rm db 7 rename db Command Option 2 displays all databases in the area After a database is opened with the option 5 the following menu is displayed Options 0 quit 1 go to main menu 2 1s 3 cd 20 show names 21 unix od Command 2 You may then list all objects in the current file option 2 change current file option 3 show all names in the database option 20 and apply the Unix od command to see the contents of a byte range of an object When option 2 is chosen the properties of objects within the current file are displayed as follows v h 20 00008001 0002 ce 001 v h 20 00008002 0002 ce 001 ln 5000 00007ffe 0002 73 001 my large obj n 40 000070fe 0002 a2 001 my small obj 40 000070fe 00
12. returns zero on success non zero on failure 26 5 11 3 Inserting and Removing Index Elements int insert const void key const void value inserts the lt key value gt pair into the index If the index is a unique key index and the key already exists then a non zero value is returned as indication for the error On success zero is returned int remove const void key const void value 0 EQ_FUNC eqf 0 removes the lt key value gt pair from the index when when value is not NULL If value is NULL all pairs whose key part is key are removed The eqf is used to find the value that has to be removed when it is provided otherwise memcmp 3 is used On success zero is returned If an error occurs non zero is returned 5 11 4 Accessing a Particular Key int count const void key returns the number of values associated with the key Zero is returned when there are no values associated with the key and a negative number is returned if the key does not exist int lookup const void key void value copies to the space pointed by value the very first value associated with key A positive number is returned when the key cannot be located and a negative number is returned when a failure occurs Zero is returned when the key is found 5 11 5 Accessing Index Properties int nbuckets void returns the number of buckets belonging to this extendible hash int depth void const returns the depth of the extendible hash directory The
13. so is the name of the object 2 1 4 File Objects File Scans and Clustering EOS file objects serve as a mechanism to gather related objects together i e objects that need to be collocated They provide facilities for sequencing through the objects they contain Files may contain other files and every object including file objects is a member of exactly one file object Thus objects form a tree where internal nodes are file objects and leaves are ordinary non file objects When a new database is created EOS automatically creates a file object that serves as the root file of this tree On the physical level a file consists of a number of single pages and or segments Pages are not shared among files Forward and backward scanning of objects in a file is supported In addition the set of objects on which the scan is performed can be restricted to the objects within a single page of the file being scanned Such page oriented file scans are useful for efficiently implementing various kinds of joins that require all objects in two or more files to be compared To improve performance clients may exercise control over the physical placement of objects within a database Specifically at object creation clients may instruct the object manager to place the new object near an existing one EOS will store the new object on the same page as the existing object if space is available in that page otherwise the new object is placed on a new page
14. stored in the buffer pool The port where the server daemon listens for connection requests The rooted path of the global log file to be used The rooted path of the checkpoint file The directory that will contain the private log files The directory must exists otherwise an error will be generated The maximum number of pages that can be locked at the same time by all active transactions communicating with the server 34 R num The maximum number of lock requests both granted and blocked that can be outstanding at any point in time T num The maximum number of active transactions that can hold locks on database pages at the same time L lock_protocolThe concurrency control protocol to be used The available protocols are 2PL and 2V2PL 2PL is the standard two phase locking protocol 2V2PL is the two version two phase locking protocol used by default in EOS e name The name of the file to be used for reporting errors If not given the stderr is used a name The directory that will contain the archived private log files If the directory does not exist an error will be reported 6 2 Normal Operation Once the server has started up it monitors the standard input stdin for user entered commands The commands that are recognized are given below help A brief description of all the available commands is given version The current EOS version number is printed on the screen checkpoint Take a checkpoint now debug The
15. the completion of abort static int is_active void returns true if the application program has already started a transaction Otherwise it returns false static int is_readonly void returns true if a transaction has begun and it is read only 5 6 EOS Objects class eosobj EOS objects are manipulated via object handles There is one handle for each object fetched from the database Having a handle to an object implies that the page the object resides on is fixed in the buffer pool i e the page cannot be replaced or moved until it is explicitly unfixed 5 6 1 Creating and Removing Objects static eosobj create int size eosdatabase db const void data 0 int flags 0 int hint 0 int ano 0 creates an EOS object of size size in the root file of the database db The new object is physically created in the EOS area whose number is ano unless ano is zero in which case it is created in the same area the database was created 18 static eosobj create int size eosfile pfile const void data 0 int flags 0 int hint 0 int ano 0 creates an EOS object of size size in the file pfile The new object is physically created in the EOS area whose number is ano unless ano is zero in which case it is created in the same area the file was created static eosobj create int size eosobj obj const void data 0 int flags 0 int hint 0 creates an EOS object of size size in the file in which the object obj belongs The new object i
16. the eosobj VAR_LENGTH flag set int is_page_object void const returns true if the object is a page object int is_index void const returns true if the object is a the directory of an extendible hash index int is_dirty void const returns true if the object has been modified by the current transaction 5 6 4 Naming Objects int name_set const char name sets the name name to the persistent object It returns zero on success non zero on failure const char name void returns the name of the object or 0 if the object has no name int name_remove void removes the name of the object It returns zero on success non zero on failure 5 6 5 Tagging Objects int utag_set void tag sets the value of the 2 byte tag associated with the object to the value of the first two bytes pointed by tag const void utag_get returns a pointer to the object s 2 byte tag 21 5 6 6 Accessing Portions of Objects Byte Range Operations Byte range operations can be applied to both small and large objects but they are specially useful for very large objects that cannot be accessed in one step A byte range offset n defines the start byte offset and the number of bytes n The first byte of the object is at offset 0 Thus for an object of size s a byte range is valid if 0 lt offset lt s and n gt 0 and offset n lt s These functions return 0 on success non zero on failure int read void buf int offset int n const r
17. the keys are the positions of the object s bytes within the segments When length changing updates byte range deletes and inserts are performed on the large object its segments may have to be broken up into smaller ones Since small segments have negative performance effect on the read operation EOS allows the client to specify a segment size threshold T a constraint on EOS not to store byte chunks in two logically adjacent segments one of which has less than T pages if they can be stored in one segment Note that the threshold mechanism does not specify fixed size segments neither a minimum number of pages per segment For example with T 16 a large object that is 2 pages and a half long is kept in three pages not in 16 pages The tradeoffs that need to be examined in order to set this value are the following See also Bil92b for performance results Larger segments lead to better storage utilization lower sequential and random read costs and higher update cost i e the only aspect of the performance that might be affected negatively by larger segments is the cost of byte inserts and deletes 2 1 7 Indexes EOS provides extendible hashing indexes FNPS79 Index keys can be variable size strings or any fixed size structure The values associated with the keys can be any fixed length structure 2 1 8 Transactions EOS provides full support for concurrency control logging and recovery Concurrency control allows multiple us
18. the obj_scan and obj_update programs concurrently open up two new windows and run the obj_scan on one and the obj_update on the other Running them concurrently may result to periodic deadlocks because both programs access the same file in the same database When a deadlock occurs the offending program is terminated 5 If you want to shut down the server go to the window where the server runs and type the following command shutdown The server will print a number of messages on the screen and when it finishes processing the shutdown command the following message appears on the screen EOS server SHUTTING DOWN Closing the shop 3 1 Compiling and Linking your Application Application programs written in C or C must include the eos h file Application programs that use persistent references must include the eos_Ref h file in addition to eos h For a C applica tion use the I option of the compiler to add the eos include directory to the list of directories the pre processor searches for include files For a C application add the eos include_c path to the list EOS offers two basic libraries client o and private o An application program that uses the EOS server must be linked with the client o library If the application program manipulates private local databases the private o library is linked with it In addition programs compiled with the C compiler must also be linked with the cfuncs o library Since the EOS librari
19. the object referenced by objRef to name Zero is returned on success and non zero of failure int remove_object_name const eosRef_Any amp objRef removes the name associated with the objected referenced by objRef Zero is returned on success and non zero of failure int rename_object const char oldmname const char new_name replaces the name of the object whose name is old_name with new_name Zero is returned on success and non zero of failure 17 const char get_object_name const eos_Ref_Any amp objRef const returns the name on the object referenced by objRef eos_Ref_Any lookup_object const char name const returns a reference to the object whose name is name The validity of the returned reference must be checked using the eos_Ref_Any is_mnull member function 5 5 Transactions class eostrans All accesses to EOS objects except database opening and closing must be done within a transaction block static int begin int rdonly 0 begins a transaction block If rdonly is true the transaction is a read only transaction and no updates within the transaction area allowed It returns zero on success non zero on failure static int commit void commits an active transaction It returns zero on success non zero on failure static int abort int normal 1 aborts an active transaction If normal is true it returns 0 on successful completion and non zero on failure If normal is false the application program exits after
20. values of all the parameters used by the server are printed on the standard output In addition information about the active processes spawned by the server is given stats A number of statistics about the server buffer and transaction modules of EOS are printed on the screen shutdown The server will be shut down after aborting all active transactions A checkpoint is taken so that no recovery is needed when the server starts up again exit Exit immediately 6 3 Server Shutdown To shutdown the server when it runs in the background or from a remote machine run eosserverkill The invocation of the above program is done in the following way eosserverkill c a w f kost The meaning of the available options is explained below host The name of the machine where the server runs 35 C Take a checkpoint and then exit immediately a Abort all active transactions present in the system and exit W Wait until all active transactions finish either commit or abort and then exit No new transaction will be started in the interim f Flush the shared buffer pool before exiting The a and w options are conflicting and the a will be used when both are present If the eosserverkill is invoked with no options the server will exit after aborting all active transactions The current release does not verify the permissions of the person invoking the eosserverkill program The server removes all shared memory segments
21. when they are finished committed or aborted When a page is locked the file containing this page is locked too in the corresponding intention mode When a file is locked in either S or X mode the pages it contains do not have to be locked explicitly This minimizes the overhead of the concurrency control module In this locking scheme a number of readers and at most one writer can be operating simultaneously on the same granule The writer has to wait for all the readers to finish before it can commit Deadlocks are handled by a variation of the depth first traversal algorithm applied on the waits for graph WFG constructed from the lock tables to determine if a cycle exists Deadlock detection is performed every time a lock request is blocked by another transaction which is blocked too If a deadlock cycle is found the requester gets aborted 2 2 2 Logging The system maintains two kinds of logs a global log and a number of private logs Each private log is associated with one transaction only The log records of a private log are redo records i e they contain the results after images of the updates generated by the corresponding transactions The global log contains records that are either commit records or checkpoint records A commit log record contains the committed transaction s id and other information related to transaction s updates The checkpoint record contains the ids of all the committed transactions at the time the checkp
22. 02 4c 002 f nv 20 00008802 0002 02 001 my file The set of dashes and characters refers to the object properties interpreted as follows r root file object f file object 1 large object n named object v variable length object p page object h hash object The object size in bytes is displayed next followed by its oid page no area no unique no slot no followed by the object s name if any 43 9 An Example of Using EOS This section presents two simple programs included in the EOS distibution the source code of these programs is in eos example directory The first program creates a number of objects that are linked together by using a number of persistent references The second programs traverses the object hierarchy down to the level which is specified in the command line argument A number of other demo programs can be found in the smae directory 9 1 File Part h ifndef __Part_h__ define __Part_h__ include eos_Ref h include eos h define NPARTS 200 define NAME_SIZE 128 struct Part int part_no The part number eos_Ref lt char gt name A name given to this part eos_Ref lt Part gt x_part Persistent reference to another part eos_Ref lt Part gt y_part Persistent reference to another part eos_Ref lt Part gt z_part Persistent reference to another part endif 9 2 File part create c Usage create lt database name gt This programs creates a hierarchy of objects
23. 5 11 4 Accessing a Particular Key 2 2 0 0 2 0 20 020000000004 27 5 11 5 Accessing Index Properties 2 0 0 2 0 000000000004 27 Index Scan class eosehashscan 2 eee eee 28 Extensions and Primitive Events class eosexten 0000 29 5 13 1 Defining Hook Functions 2 0 00 00 00 002002000004 29 5 13 2 Return Values of User Functions aoaaa 30 5 13 3 Argument Passed to User Functions 00 000 000 30 5 13 4 Primitive Events 2 2 0 0 0 0 02 2 0 0 000000 30 5 13 5 Extension Activation Status 2 a 32 iii 5 13 6 Example 1 Access Control 2 0 2 ee ee ee 5 13 7 Example 2 Fixing C Pointers 0 6 The EOS Server 6 1 Server Startup 2 2 ee 6 2 Normal Operation aaa a ee 6 3 Server Shutdown 2 2 ee 6 4 Checkpoint 2 0 ee 6 5 Is Alive aoaeaaiaee 7 EOS Customization 7 1 Customizing the Area Formatting Procedure formatrc 00 7 2 Customizing the Client clientrc 2 0 0 00000 0000004 7 3 Customizing the Server serverre osaa 8 EOS File System Viewer cosfsview 9 An Example of Using EOS 9 1 File Part h ee 9 2 Filepart_create c oaoaraa 9 3 File part traverse c aaau 10 Troubleshutting 11 Release Notes 38 38 39 40 43 44 44 44 46 48 49 1 Introduction EOS is a storage manager being developed at AT amp T Bell Labs for the fast development of high perform
24. 6 The EOS Server 6 1 Server Startup The EOS server is started up by executing the following command eosserver h v c 1 r b t num f secs s service B npages E Mbytes p port J name C name P name 0 num R num T num L lock_protocol e name a name The meaning of each one of the available command line arguments is presented below t num f secs s service B npages E Kbytes p port J name C name P name 0 num A brief explanation for each command line argument is displayed on the screen Verbose mode It displays messages regarding the progress of the server In this way the behavior of the server can be studied It turns off the lock manager No locks will be acquired for any kind of access to the database It turns off the log manager No log records are generated Starts the server without performing recovery The server can run in the background if the amp shell flag is used The v option is ignored in this case The maximum number of client programs that can be connected to the server at the same time The frequency in seconds of the checkpoint process The name of the service offered as it is in the etc services file if such service exists The size of the buffer pool used by the server in terms of pages 4 Kbytes each The size of the extra space used by the server for large object manipulation because large objects do not get
25. EATE Captured by the eosobj create Members set BEFORE pfile oid flags size hint Members set AFTER obj pfile oid flags size hint The obj member of the eosstat structure is returned when by the eosobj create when the user registered function returns eosexten RETURN OBJECT REMOVE Captured by the eosobj destroy Members set BEFORE obj Members set AFTER none OBJECT_UPDATE Captured by a number of EOS functions when an object is going to be updated or it is updated for the very first time Member Set obj SLOTTED_PAGE_FAULT Captured by a number of function in the lower level of the EOS storage manager Only the eosexten AFTER can be specified Member Set oid The user registered function is called for every object in the page that just fetched in the local buffer 5 13 5 Extension Activation Status static int alter int type int when int extno int on_off activates and de activates a registered function The extension with number extno registered to be called when the event type occurs is de activated if the value of on_off is 0 and it is activated when on_off has the value 1 A registered action is by default active static int is_active int type int when int extno checks whether the extension extno for the event type when is active or not 5 13 6 Example 1 Access Control This example demonstrates the use of EOS extensions to provide access control such as when certain databases should not be ac
26. EOS User s Guide Release 2 2 For UNIX based Systems Alexandros Biliris Euthimios Panagos 600 Mountain Avenue AT amp T Bell Laboratories Murray Hill NJ 07974 biliris thimios research att com Abstract EOS is astorage manager providing key facilities for the fast development of high performance database management systems and persistent languages This document provides a brief overview of the EOS Release 2 2 architecture facilities information on using the system including exam ples and setting up tuning parameter values to adjust EOS performance Contents 1 Introduction 1 1 1 Contact for Further Information 0 0 0 0 020000 0222 eee 2 2 EOS Architecture and Facilities 3 2 1 Basics 2 aaa 3 2 1 1 Databases and Storage Areas 2 ee ee 3 2 1 2 Object Identifiers OIDs 2 0 0 ee een 3 2 1 3 Named Objects 0 0 2 a 3 2 1 4 File Objects File Scans and Clustering 4 2 1 5 Object Representation and Object Handles 4 2 1 6 Large Objects 0 ee 5 2 1 7 Indexes 2 2 ee 5 2 1 8 Transactions ansaa aa ee 5 2 2 The EOS Client Server Architecture aaao 0202 eee ee eee 6 2 2 1 Concurrency Control aoaaa ee ee 7 2 2 2 Logging 2 e 7 2 2 3 Transaction Commit and Abort 2 0 0 0 a 7 2 2 4 Checkpoint oaa ee 7 2 2 5 Recovery from System Crash Restart 0 0 ee en 8 2 3 Advanced Features oaoa ee 8 2 3 1 Page Objects and Pla
27. Line e The server can now run in the background Use b flag and the amp shell flag See Section 6 1 e Error messages of the server can be stored in a user specified file Use the e flag See Section 6 1 e The archived private log files can now be stored in a user specified directory by using the a flag at start up time See Section 6 1 e The eosareadelete invalidates all the pages belonging to the deleted area that are present in the buffer pool of the server 49 e The eosareaformat invalidates all the pages present in the server s buffer pool that belong to the area being formatted when the area exists already e Abnormal client failures are detected by the server by using a timeout period as given by the user specified value of EOS_TR_FAIL_TIMEOUT e eofsview is a primitive and not yet complete interactive browser that shows information about an EOS storage area databases files and objects See section 8 50 References BDG93 BGL 93 Bil92a Bil92b Cat93 FNPS79 GR93 KP84 Ste90 Str87 A Biliris S Dar and N Gehani Making C objects persistent The hidden pointers Software Practice and Experience 23 12 1285 1303 December 1993 A Biliris N Gehani D Lieuwen E Panagos and T Roycraft Ode 2 0 User s Manual Technical report AT amp T Bell Laboratories 1993 A Biliris An efficient database storage structure for large dynamic objects In Pro
28. When the checkpoint procedure completes a checkpoint record is inserted in the global log file and the location of this checkpoint record is saved on a well known location The EOS checkpoint is non blocking new transactions can begin and active transactions may continue accessing the server and its resources while the checkpoint activity takes place 2 2 5 Recovery from System Crash Restart If a system crash occurs the EOS server returns the database to the last consistent state it was in before the failure This is done by scanning the log file and redoing all the updates made by committed transactions in exactly the same order as they were originally performed After the database state has been restored a checkpoint is taken and the system is operational again If a system failure occurs while the restart is performed the subsequent restart performs the same work again in an idempotent fashion The restart procedure of EOS is fast for two reasons a only one forward pass over the log is required and b the log itself is short because only after images of updates are logged EOS provides continuous archiving of the private log files The archiving process is activated by the global log manager every time a checkpoint is taken and the number of the log files generated since the last archive is greater than some threshold value The private log files created since the last time the archive process was executed are compressed and merged togethe
29. an AUTO_FWRD Automatic scan of the index in forward order Initialy the cur sor is positioned at the first pair of the index if key is NULL otherwise it is positioned at the first pair whose key is key eosehashscan AUTO_BWRD Automatic scan of the index in backward order Initialy the cursor is positioned at the last pair of the index if key is NULL otherwise it is positioned at the last pair whose key is key eosehashscan MANUAL Explicit movement of the cursor int cursor int same_key 0 returns true if the cursor currently points to a valid lt key value gt pair If the scan order is eosehashscan AUTO_FWRD or eosehashscan AUTO_BWRD the cursor moves to the next or previous pair respectively If the value of same_key is true the cursor is restricted to visit only those pairs whose key is the same as the key of the currently pointed pair In other words if same_key is always true the cursor will visit all pairs with a particular key The cursor will remain unchanged if the scan order is eosehashscan MANUAL const void key void returns a pointer to the key pointed by the cursor Zero is returned when the cursor does not point to a valid lt key value gt pair const void value void returns a pointer to the values pointed by the cursor Zero is returned when the cursor does not point to a valid lt key value gt pair int remove void removes the value curently pointed by the cursor If this is the only one valu
30. ance database management systems The following is a brief summary of the facilities provided by EOS e Extensive support for large objects Objects can be accessed transparently in the client s cache without incurring any in memory copying cost or via byte range operations such as read write append insert delete bytes etc specially suited for very large multimedia objects e Any object can be named for fast retrieval Referential integrity between named objects and their corresponding names is enforced by EOS e Page objects objects that expand over the entire available space in a page which can be accessed in the same way as any other object e Plain database pages belonging to a particular storage area They can be used to build index structures We used them to build our extensible hashing e Extensible hashing supporting variable size keys and user defined hash and equality functions e Database files for grouping related objects together Databases as collections of files and objects Databases are stored in one or more storage areas UNIX files or disk raw partitions and each such area may contain many databases Clustering hints for the physical placement of objects in pages files databases and areas e A simple and powerful mechanism that allows users to enhance and even modify the EOS functionality without compromising modularity by associating hook functions with certain primitive events EOS traps the events as
31. and semaphores used when it exits However there might be cases where there are leftover shared memory segments and semaphores e g if the server is killed by the kill 9 command Because the server will not operate properly if these leftovers are not removed use the ipcrm system command to remove them The ipcs command is used to check if there are any shared memory segments and semaphores left 6 4 Checkpoint The frequency of the checkpoint procedure is set by the f command line option of the eosserver command In addition the eoscpfrequency utility program can be used to change the checkpoint frequency while the server is running Its usage is as follows eoscpfrequency host secs The time period between two successive checkpoint requests is given by the secs argument passed to the above program If the hostis not given then the host given by the EOS_SERVER_HOST_NAME variable will be contacted Currently there is no limit on the upper bound of the checkpoint period This might be changed 6 5 Is Alive The command eosserveralive checks if the EOS server is alive eosserveralive host If the host is given then this particular host will be contacted Otherwise the host name will be taken from the EOS_SERVER_HOST_NAME environment variable see section 7 3 If the EOS server is active then the EOS server is alive and healthy 36 message will appear on your screen Otherwise the No EOS server is running on host
32. aptured by the eostrans begin Members set rdonly Captured by the eostrans commit Members set none Captured by the eostrans abort Members set normal Captured in various levels of the EOS storage manager Members set none Captured by the eosdatabase open Members set BEFORE db rdonly create trunc Members set AFTER db rdonly create trunc The db member of the eosstat structure is returned by the eosdatabase open when the user registered function returns eosexten RETURN Captured by the eosdatabase destroy Members set BEFORE db Members set AFTER none Captured by the eosfile create Members set BEFORE pfile name flags Members set AFTER file pfile name flags The file member of the eosstat structure is returned by the eosfile create when the user registered function returns eosexten RETURN Captured by the eosfile open Members set BEFORE oid Members set AFTER file oid The file member of the eosstat structure is returned by the eosfile open when the user registered function returns eosexten RETURN Captured by the eosfile destroy Members set BEFORE file Members set AFTER none Captured by the eosobj get Members set obj Only the eosexten AFTER can be specified for this event The obj member of the eosstat structure is returned when by the eosobj get when the user registered function returns eosexten RETURN 31 OBJECT_CR
33. as they occur and causes the actions that applications associated with these events to be executed Actions for a particular event are executed in the order in which they were registered This facility can be used to extent the EOS functionality in many ways e g to to collect statistics on object faults or transaction commits or to set access privileges so that only certain users can access an object or a file in the database or the database itself As another example a hook may be registered that restarts a transaction after it is being aborted due to a deadlock 3 Getting Started with EOS To access the binaries and man pages in the eos directory set your path and manpath environment variables to include the eos bin and eos man directories respectively The following shows how to do this assuming that EOS is installed in usr eos If you use csh or tcesh place the following in your cshre set path path usr eos bin setenv MANPATH MANPATH usr eos man If you use Bourne or Korn shell place the following in your profile PATH PATH usr eos bin export PATH MANPATH MANPATH usr eos man export MANPATH The rest of this section describes the simplest way of configuring the EOS storage manager and running the three example application programs obj_create obj_scan and obj_update included in the eos example directory of the EOS distibution The obj_create creates a number of objects and puts them in a named file belongin
34. ceedings of the Fighth International Conference on Data Engineering Tempe Arizona pages 301 308 February 1992 A Biliris The performance of three database storage structures for managing large ob jects In Proceedings of ACM SIGMOD 1992 International Conference on Management of Data San Diego California pages 276 285 May 1992 R G G Cattell Object Database Standard ODMG 93 Morgan Kaufmann San Mateo California 1993 Contributions by T Atwood J Dubl G Ferran M Loomis and Wade D R Fagin J Nievergelt N Pippenger and H R Strong Extendible hashing a fast access method for dynamic files ACM Transactions on Database Systems 4 3 315 344 September 1979 J Gray and A Reuter Transaction Processing Concepts and Techniques Morgan Kaufmann San Mateo California 1993 B Kernighan and R Pike The UNIX Programming Environment Prentice Hall Soft ware Series 1984 R Stevens UNIX Network Programming Prentice Hall Software Series 1990 B Stroustrup C Programming Language Addison Wesley Reading MA 1987 2nd ed 51
35. cessible to all users Let us assume that the application keeps a table of databases and the users that have access to them and that the function access_authorized char dbname char uname returns true if the user with name uname has access to database with name dbname We want to define an extension that is triggered just before a database is going to be opened That is the event that triggers this extension is BEFORE DB_OPEN The first step is to write the hook we want to be executed when the above event occurs its code may look as follows int check_db_access eosstat s if access_authorized s gt name getlogin printf s permission denied for this database n s gt name return eosexten RETURN 32 return eosexten CONTINUE After the action is written the second and final step is to register this extension with EOS as follows eosexten insert eosexten DB_OPEN eosexten BEFORE check_db_access Before any attempt to open a database EOS sets the name field of the eosstat structure to the name of the database and invokes the function check_db_access In turn the function checks whether the user is authorized to access the database with the given name If the user has access to this database the function returns eosexten CONTINUE This return value signals EOS to follow its normal flow of control which is to go ahead and open the database On the other hand if the user does not have access to thi
36. ct s creation This is useful when the object is large and the user intents to create the object in pieces by successive appends If this option is specified the value returned by mptr is garbage and the object can be accessed only via the byte range operations described in section 5 6 6 19 eosobj VAR_LENGTH It creates a variable length object Length changing updates can be applied on this object by using the byte range function calls described in section 5 6 6 int destroy void removes this object It returns zero on success non zero on failure 5 6 2 Accessing Objects static eosobj get const eosoid amp oid int flags 0 returns a handle to the object with id oid On failure it returns NULL The flags value is constructed by ORing constants from the following list eosobj DIRTY The object is marked dirty eosobj HDR_ONLY If the object is large the header of the object only is fetched If this option is specified the value returned by mptr is garbage and byte range operations must be used to access the object static eosobj get const eosdatabase db const char name int flags 0 returns a handle to the object with name name in the database db The argument flags is used as explained above int release void releases the handle for an object It returns zero on success non zero on failure void mptr void const returns the memory address of the object in the local buffer pool If the application i
37. d by a transaction are stored in a file whose name has the form eos priv_x_y_z under the above directory EOS_ARCHIVE_DIR_PATH The rooted path name of the directory used to store the archived private log files The name of an archive file has the form eos_arch_N Z where N refers to the order of creation and it is a monotonically increasing number EOS_LOG_THRESHOLD The minimum number of private log files that have to be created before the archive procedure is activated The value of this variable depends on the expected size of the log files created If the log files are small then a large number hundreds is adequate On the other hand if the log files created are big a small value tens is recommended EOS_MAX_LOCK_UNITS The maximum number of database pages that can be locked at the same time EOS_MAX_LOCK_ENTRIES The maximum number of locks held by all transactions present in the system on different database pages EOS_MAX_TRANSACTIONS The maximum number of active transactions that have at least one lock entry at the same time EOS_SRV_SND_BUFFER The size in kilobytes of the operating system s buffer used to send data over a TCP IP connection This value should not exceed the upper bound imposed by the kernel The default value is 17K 41 EOS_SRV_RCV_BUFFER The size in kilobytes of the operating system s buffer used to receive data over a TCP IP connection This value should not exceed the upper bound imposed by the
38. disk access which is the cost of fetching the page in which the object is stored no additional cost is involved in translating an oid because it is a physical database address After an object handle is acquired the speed of subsequent accesses to the object is almost the same to that of an in memory dereference of a pointer to resident data This is because persistent objects can be manipulated directly on the page on which they reside without incurring any in memory copying cost 2 1 6 Large Objects EOS has been designed to handle arbitrary large objects provided that physical storage is indeed available and accessible Technically speaking an object is small if it can fit entirely in a single page otherwise it is large Small objects may become large and vice versa Large objects can be accessed and updated in exactly the same way as small objects Thus the manipulation of large objects is transparent to the applications For very large objects however users may want to access portions of the object EOS provides operations that deal with a specific byte range within the small or large object read or write a random byte range within the object insert or delete bytes at arbitrary positions within the object and append bytes at the end of the object Large objects are stored in a sequence of variable size segments which are allocated as explained in section 2 1 1 These segments are then pointed to by a tree structure in which
39. does not invoke EOS 2 s overloaded new operators for objects that are of a nonclass type and arrays of class objects In this case the eosobj create function should be used 5 3 Persistent References class eos Ref Objects may refer to other objects through a persistent reference called an eos_Ref Persistent references are valid across transaction boundaries as well as across databases The class eos_Ref is parameterized with a parameter for indicating the type of the object being referenced by the persistent reference This means that eos_Ref must be used by enclosing in angle brackets the name of the referent type For example we can define a persistent reference to an object of type employee in the following way eos_Ref lt employee gt emp EOS also provides an eos _Ref_Any class that provides a generic reference to an object of any type The eos_Ref class provides an operator for performing the conversion from a reference to an object of type T to an eos Ref_Any according to the ODMG 93 Cat93 standards eos_Ref void the default constructor for this class The persistent reference is initialized to NULL eos Ref T from0bj constructs the persistent reference to an object of type T given a virtual memory pointer to that object eos_Ref const eos_Ref lt T gt amp constructs the persistent reference to an object of type T given a persistent reference to that object eos_Ref const eos_Ref_Any amp constructs the p
40. e associated with the key then the key is removed too It returns zero on success non zero on failure int replace_value const void new_value replaces the value that is currently being scanned with new_value Zero is returned on success and non zero if no value is being scanned or an internal error occurs 28 int close void closes an open scan It returns zero on success non zero on failure When the eosehashscan MANUAL order is specified the cursor must be moved explicitly by using the following functions They all return zero on success non zero on failure Note that it is NOT an error to seek to the first next previous or last lt key value gt pair when no such pair exists in the index In this case a call to cursor will simply return false int first int same_key 0 positions the cursor to the first value of the current key if the value of same_key is true or to the first value of the first key in the index if its value is false int last int same_key 0 positions the cursor to the last value of the current key if the value of same_key is true or to the last value of the last key in the index it its value is false int next int same_key 0 positions the cursor to the next value of the current key If the value of same_key is false and there are no other values for the same key then it positions the cursor to the first value of the next key in the index int prev int same_key 0 positions the cursor to the p
41. e object with id oid It is an error to attempt to position the cursor on an object that does not exist or it is not an immediate member of the file being scanned 24 5 9 Page Objects class eospageobj class eospageob public eosobj static eospageobj create eosfile pf int flags 0 int ano 0 const eosoid amp near eosoid null creates a page object in file pf and returns the handle to the new object it return NULL on failure The rest of the arguments are the same with the ones of eosobj create 5 10 Plain Database Pages class eospage EOS provides direct access to plain pages An application program can create destroy pin in the local buffer pool and unpin a plain database page belonging to any storage area A plain page is associated only with the storage area it belongs to int create int ano allocates and pins down in the local buffer pool a new plain page in the storage area ano It returns zero on success non zero on failure int destroy void unpins the plain page associated with this and it returns the page to the storage area it belongs It returns zero on success non zero on failure static int destroy eosspid pno int ano frees the page pno belonging to the storage area ano If the page appears in the local buffer pool it is invalidated It returns zero on success non zero on failure int pinCeosspid pno int ano int flags 0 pins down in the local buffer pool the page pno belonging to the sto
42. eads n bytes of the object starting at offset offset into the buffer pointed by buf int write const void buf int offset int n replaces overwrites n bytes of the object starting at offset offset with the first n bytes pointed to by buf int append const void buf int n int hint appends the first n bytes pointed to by buf at the end of the possibly 0 size object The hint can be used when the object is written with several append operations and it indicates an estimate of the total object size If the precise size of the object is not known it is always good to overestimate the size The hint is taken into consideration only if its value is greater than the sum of n and the current object size int insert const void buf int offset int n inserts the first n bytes pointed to by buf into the object starting at offset offset None of the existing bytes is overwritten int delete_range int offset int n deletes n bytes of the object starting at offset offset Deleting all bytes of an object does not delete the object itself int truncate int offset deletes all bytes on the right of and including byte offset of the object The size of the object becomes offset 5 7 File Objects class eosfile class eosfile private eosobj EOS treats files in the same way as it treats objects A file can be created within another file and a file can have a name as any other object static eosfile create eosfile pfile const char name 0
43. ers to access a database at the same time in a consistent way When a transaction is committed all its updates are permanently posted to the database When a transaction is aborted by the user the recovery s goal is to make the database look like as if the aborted transaction was never submitted for execution The storage manager may also abort a transaction when it is the victim of the deadlock detection algorithm or when the system malfunctions In addition when the system restarts after a crash the database reflects the updates of all the committed transactions prior to the crash See GR93 for a description on transaction processing EOS Server a Buffer Disk I O _ Management Logging 1 1 Maea m hiia E E Paeahi See i eee a cee cece ee a 1 1 Adminstration Transaction Management Recovery Management Communication Network Client 1 Client N Communication Transaction amp Lock Log subsytems Cache Communication Cone ee E a Pee Transaction amp Lock Log subsytems Cache Interface Interface Application Application Figure 1 The client server architecture of EOS 2 2 The EOS Client Server Architecture Figure 1 sketches the EOS client server architecture The EOS server is a multi threaded daemon process that mediates all the accesses made to the database To avoid bl
44. ersistent reference to an object from a generic reference eos_Ref the destructor for this class operator eos_Ref_Any void const converts an eos _Ref lt T gt to an eos_Ref_Any void clear void sets the persistent reference to NULL int is_null void const return true if the persistent reference is NULL int delete_object void deletes the object that is referenced by this persistent reference 15 T ptr void const returns a memory pointer to the object referenced by the persistent reference The pointer is only valid until the end of the transaction or until the object it points to is deleted T operator gt void const dereferences the persistent reference and returns the valid T for which the specified reference is a substitute T amp operator void const dereferences the persistent reference and returns the valid T for which the specified reference is a substitute eos Ref amp operator T eos Ref amp operator const eos_Ref lt T gt amp eos Ref amp operator const eos_ref_Any amp these operator are used for copy assignment friend int operator const eos_Ref lt T gt amp refL const eos_Ref lt T gt amp refR friend int operator const eos_Ref lt T gt amp refL const T ptrR friend int operator const T ptrL eos_Ref lt T gt amp refR friend int operator const eos_Ref lt T gt amp refL const eos_Ref_Any amp anyR friend int operator const eos_Ref_Any amp
45. es have been generated by a C compiler the linking must be done with a C compiler 11 4 Formatting And Deleting Storage Areas Storage areas are created formatted and removed by invoking EOS commands at the UNIX prompt An area can be either a UNIX file or a disk raw partition the latter must already exists in order for EOS to format it As it was mentioned in Section 2 1 1 an area cam be either shared and private Shared areas are accessed via the EOS server Private areas are created on the local machine of the user creating the area The file eos areas of the server account keeps information about all areas formatted by the server Information about a private area is kept in the eos areas file of the user formatting the area 4 1 Formatting Areas eosareaformat The command eosareaformat formats an EOS storage area If the area is a UNIX file and the file does not exist eosareaformat creates it first The rooted path name of the area being formatted must be specified when the command is invoked For example eosareaformat usr thimios eos_area formats the UNIX file usr thimios eos_area In general an area name has the following form L host_name rooted_area_path where host_name is the machine name the server is running on If it is not specified the name of the area manager s host machine is taken from the the EOS configuration file eos formatrc see section 7 1 The complete set of command line argument
46. es not support shared memory Solution ask the system administrator to install shared memory on this machine 2 The number of the available shared memory segments is not enough to satisfy the server s requirements Solution decrement the EOS_SHARED_POOL_SIZE value 3 A conflict was created because the key used to create a shared memory segment has been already used by someone else Solution remove any shared memory segments used by other processes because some of the keys used for creating shared memory are fixed 4 The server was shut down and was not able to cleanup the shared memory segments it used Solution check if there are any shared memory segments left by using the ipcs m com mand If there are some remove them by using the ipcrm command Cannot create semaphore This may happen when 1 The machine where the server started on does not support semaphores Solution ask the system administrator to install semaphores on this machine 2 The number of the available semaphores is not enough to satisfy the server s requirements Solution ask the system administrator to increase the number of the semaphores that can be created system wise 3 A conflict was created because the key used to create a semaphore has been already used by someone else Solution remove any semaphores used by other processes because some of the keys used for creating semaphores are fixed 48 4 The server was shut down and was not able to c
47. g to a database The obj_scan reads all the objects created and prints them on the screen Finally the obj_update randomly updates several of the created objects Go to the eos example directory and compile these programs to be ready for execution These are the steps that have to be followed 1 Install the configuration files by running the following three programs eosformatenv eosclientenv eosserverenv These programs create the files formatrc clientrc and serverrc respectively in the directory eos under your home directory 2 Start the server Open a new window and go in the bin directory where the eosserver executable is To start up the server type eosserver When the server is ready to accept requests the following message appears on the screen EOS server We are open for business 3 Create and format a storage area Let us assume that you want to create an EOS storage area in the UNIX file usr sue area Run the command 10 eosareaformat usr sue area You are now ready to create databases in this area and populate it with objects 4 Run the obj_create to create a number of objects in a database belonging to the area you have just created To create 1000 objects type the following obj_create usr sue area myfirstdb 1000 To read the objects you have just create type obj_scan usr sue area myfirstdb To update few of the objects you have just create type obj_update usr sue area myfirstdb If you want to run
48. imates unique oids unsigned sno 10 slot number in the page that points to the object static const eosoid null is the null object id int is_valid void const returns true if the oid is a valid object id i e there exists an object with such id otherwise it returns false int operator const eosoid amp oid const int operator const eosoid amp oid const int operator gt const eosoid amp oid const int operator lt const eosoid amp oid const int operator gt const eosoid amp oid const int operator lt const eosoid amp oid const return true if this and oid satisfy the corresponding relational operator 5 2 Persistent New class eos_new Persistent object are created by either using the eosobj class described in Section 5 6 or by using the overloaded operator new provided by EOS EOS s persistent new takes one argument which specifies where the new persistent object is going to be placed Persistent objects can be placed in an EOS database or in an EOS file or they can be placed close to another persistent object The interface provided is the following void operator new size_t size const eosdatabase db void operator new sizet size const eosfile pfile void operator new size_t size const eosobj obj void operator new sizet size const eos_Ref_Any amp ref0bj 14 The EOS persistent new returns a pointer to the data part of the newly created persistent object CAUTION The SPARCompiler C 4 0
49. in Pages oaaae 8 2 3 2 Extensions and Primitive Events aoaaa a 8 3 Getting Started with EOS 10 3 1 Compiling and Linking your Application oaoa aaa e 11 4 Formatting And Deleting Storage Areas 12 4 1 Formatting Areas eosareaformat oaoa 00000000000 12 4 2 Deleting Areas eosareadelete ooo oa a 13 ii 5 The EOS Client C Interface 14 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 5 9 5 10 5 11 5 12 5 13 Object ID class eosoid 2 en 14 Persistent New class eosmew 2 2 e ee 14 Persistent References class eos_Ref o oo aa 00000000000 15 Databases class eosdatabase nooo aa e ee 16 Transactions class eostrans 2 0 e ee 18 EOS Objects class eosobj o aaa ee ee 18 5 6 1 Creating and Removing Objects aaau a 18 5 6 2 Accessing Objects auaa a 20 5 6 3 Object Properties oaoa aaa ee 20 5 6 4 Naming Objects aaa ee ee 21 5 6 5 Tagging Objects aao ee ee 21 5 6 6 Accessing Portions of Objects Byte Range Operations 22 File Objects class eosfile 2 2 ee ee ee 22 File Scan class eosfilescan ooo eee 23 Page Objects class eospageobj 2 ee 25 Plain Database Pages class eospage 1 2 eee eee 25 Extendible Hashing eosehash 2 2 ee ee 26 5 11 1 Creating and Destroying Indexes 0 0 0 0004 26 5 11 2 Accessing Indexes 2 2 2 2 ee ee 26 5 11 3 Inserting and Removing Index Elements 0 27
50. leanup the semaphores it used Solution Check if there are any semaphores left by using the ipcs s command If there are some remove them by using the ipcrm command Error 1302 occurred on the EOS server This may happen when the application tries to access a storage area that is not known to the server This can be a result of 1 Name misspelling 2 Creation of the area with the 1 flag while the server was running 3 The application was connected to the wrong server Error 1701 occurred on the EOS server This may happen when the maximum value for either of EOS_MAX_LOCK_UNITS EOS_MAX_LOCK_ENTRIES and EOS_MAX_TRANSACTIONS is exceeded Either increase their values in the serverc configuration file or use larger numbers when you use the command line arguments when starting up the server 11 Release Notes EOS 2 2 0 versus EOS 2 1 0 e A parametarized class to be used as a persistent reference to an object has been added This class obeys the ODMG 93 Cat93 standards e Persistent object can also be created by using the overloaded operator new which takes one argument that specifies where the new persistent object is going to be placed EOS 2 1 0 versus EOS 2 0 x e Reported bugs have been fixed and a number of changes have been made to increase perfor mance e The system now runs on SGI Suns 4 1 x and Solaris 2 x architectures C compilers that can be used include the ones distributed by AT amp T Sun GNU and Center
51. ntents to update the object then the EOS storage manager must be informed before the update materializes so that the right locks are requested This can be done either when get is called by passing the eosobj DIRTY flag or by using touch int touch void marks dirty the objects referenced by this fetch_all void fetches the entire object in the application s space It has no effect if the object is small or the object is large and it is already fetched in This is useful when the handle to this object was obtained by using the eosobj HDR_ONLY flag Thus applications may get an object with eosobj HDR_ONLY set examine the header and then decide whether they want the entire object 5 6 3 Object Properties int size void const returns the size of the object in bytes const eosoid amp oid void const returns the object id of the object 20 const eosoid amp parentoid void const returns the object id of the file containing the object const eosoid amp rootoid void const returns the object id of the database s root file containing the object int is_root void const returns true if the object is the root file int is_file void const returns true if the object is a file object int is_large void const returns true if the object is large int is named void const returns true if the object has a name int is_var_length void const returns true if the object is variable length i e it was created with
52. ocking UNIX disk I O system calls the EOS server creates a separate disk process to handle the I O requests for a storage area the very first time this area is accessed In this way disk I O is performed in parallel Dynamic creation and deletion of storages areas is also hanled by the server it plays the role of the area manager process and the current release can virtually support up to 6000 different areas At start up time the server spawns the checkpoint and the global log processes and creates a number shared memory regions and semaphores by using the UNIX System V shared memory memory mapping and semaphore facilities The EOS server runs as a separate process on the same or on a different machine than a client application program The communication between the server and the client workstations is done by using reliable TCP IP connections over UNIX sockets Ste90 The server buffer pool is stored in shared memory and the disk processes access it directly Semaphores provide controlled access to the structures shared by all threads and disk processes message queues and UNIX domain sockets KP84 Ste90 provide the interprocess communication among the threads and the I O requests directed to the disk processes 2 2 1 Concurrency Control Concurrency is controled by a page level mulrigranularity 2 Version 2 Phase locking MG 2V 2PL protocol Transactions acquire locks on data items before they access them and they release all locks they hold
53. oint took place along with the offset in the global log of their commit log record 2 2 3 Transaction Commit and Abort EOS recovery is based on the NO UNDO REDO protocol Transaction updates are applied to the transaction s private cache and they are posted to the database only after the transaction is committed When a transaction commits the transaction updates recorded in its private log are flushed out on stable storage a commit log record is inserted into the global log and the global log is flushed on stable storage If all steps are successful the transaction is declared committed When a transaction is aborted its private log is simply discarded and its locks are released Recovery for large objects differs from that mentioned above First large objects are not buffered in the server s shared pool Secondly updates on large objects are applied directly to the database without however overwriting the object in the database When a transaction gets aborted the changes it made on the extent s directory which keeps track of free pages are thrown away In addition no other transaction can see these changes because of the write lock held on the page containing the large object directory 2 2 4 Checkpoint To reduce the amount of work the recovery manager has to do during system restart the EOS server periodically issues checkpoints During a checkpoint dirty pages buffered in the shared pool are flushed to the stable storage
54. orks on Sun SPARC architectures running SunOS 4 1 x and SOLARIS 2 x SGI MIPS architecture running IRIX 4 x and 5 x and IBM RS6000 running AIX 1 1 Contact for Further Information For inquires about EOS and a copy of the EOS system please send e mail to Alex Biliris at biliris research att com or write to EOS Project Group c o A Biliris AT amp T Bell Labs Room 2C 221 600 Mountain Av Murray Hill NJ 07974 For bug reports please send e mail to eos research att com 2 EOS Architecture and Facilities 2 1 Basics 2 1 1 Databases and Storage Areas Databases are collections of files and ordinary objects A database is created in one of the available storage areas UNIX files or disk raw partitions The objects a database contains may be stored either in the area where the database was created or in other areas Thus a database may physically extend over many areas Also there may be areas in which no database has been created and they contain objects from different databases Storage areas are either shared or private Shared areas are accessed via the EOS server that offers control for multi user access to the area as well as recovery Private areas are created on the local machine of the user creating the area Access to private areas is in general faster compared to shared areas because all operation are carried out locally with no calls to the server However no concurrency control and recovery is offered for private areas
55. r on a single file 2 3 Advanced Features 2 3 1 Page Objects and Plain Pages Page objects are fixed length object that expand in size over the entire available space of a page They are useful in building various index structures such as B trees and hash tables An object is specified to be a page object when it is created after that it is accessed in exactly the same way as ordinary objects Plain pages are pages belonging to a particular storage area and they do not contain any control information i e the entire space of the page is available to the application Plain pages can be used for building index structures 2 3 2 Extensions and Primitive Events EOS allows users to extend and even modify the functionality of EOS by associating actions that are executed when certain primitive events occur Extensions provide a degree of extensibility without compromising modularity Primitive events are low level events that occur at various software layers of EOS such as page fault object fault object update transaction commit etc Applications can associate one or more hook functions with a particular event This registration process is usually performed at the beginning of a program before any access to the database is initiated For some events such as transaction commit applications will have to specify if the action should be executed just before or just after the occurrence of the event The EOS event manager traps primitive events
56. rage area ano If the value of flags is eospage DIRTY then an exclusive lock is acquired on this page otherwise a shared lock is obtained It returns zero on success non zero on failure int unpin int flags 0 unpins the page pointed by this If the value of flags is eospage UNLOCK then the lock held on this page is released It returns zero on success non zero on failure int touch int flags marks the page pointed by this dirty when flags have the value eospage DIRTY This means that an exclusive lock is acquired on the page It returns zero on success non zero on failure void mptr void returns a memory pointer to the page const eospid amp pid void returns the eospid id of the page pointed by this int size void returns the size of the page 25 5 11 Extendible Hashing eosehash EOS provides extendible hashing indexing facility that associates keys with fixed size values More information about the extendible hashing can be found in FNPS79 The keys can be either fixed length structures or variable length strings In addition user defined key hash and key equality functions may be provided 5 11 1 Creating and Destroying Indexes static eosehash create eosfile pfile unsigned key_size unsigned val_size int unique int string int init_size HASH_FUNC hashf 0 EQ_FUNC eqf 0 int ano 0 creates a new extendible hash index and returns the address of the handle created on success On failure it re
57. re performed on large objects such as when inserting or deleting a number of bytes starting at an arbitrary offset within the large object See section 2 1 6 for the effects of this value EOS_OH_INCREMENTS The number of object handles that will be allocated when new ones are needed There is no explicit upper bound on the number of objects fetched However such limit is implicitly imposed by the number of object present in the pages the cache can fit as specified by the EOS_POOL_SIZE variable 39 EOS_EM_MAX_ACTIONS The maximum number of hook functions that can be registered for execution for a particular event For example if this value is 4 you can register up to 4 actions to be executed before the event occurs and up to 4 actions to be executed after the event occurs EOS_SERVER_HOST_NAME The host machine name the server is running on This name is used when no host name is provided while opening creating or deleting a database EOS_SERVER_HOST_PORT The port name through which communication with the server will take place This value must match the corresponding value set at the server s environment or the value in the etc services entry when the service provided by the server is known 7 3 Customizing the Server serverrc The following are the environment variables used by the EOS server EOS_SERVER_HOST_PORT The port number where the EOS server listens for connection re quests This number must be well known to all the
58. revious value of the current key If the value of same_key is false and there are no other values for the same key then it positions the cursor to the last value of the previous key in the index int seek_at const void key positions the cursor on either the first or the last value associated with key when the order specified in eosehash open was eosehashscan AUTO_FWRD or eosehashscan AUTO_BWRD respectively If the order was eosehashscan MANUAL the cursor is not positioned at any value It is an error to attempt to position the cursor on an lt key value gt that is not valid i e the key does not exist 5 13 Extensions and Primitive Events class eosexten 5 13 1 Defining Hook Functions static int insert int type int when int func eosstat stat registers the hook function func to be executed when the event type type occurs The value of the when argument determines if the hook is called before or after the occurrence of this event and it can take one of two values eosexten BEFORE the hook is invoked just before the event occurs eosexten AFTER the hook is invoked just after the occurrence of the event On success a non negative number is returned called the extension number On failure 1 is returned 29 5 13 2 Return Values of User Functions The user function func must return one of the following values eosexten FAIL The user function func failed Then the EOS component that called func fails too
59. rned off EOS_MAX_CONNECTIONS The maximum number of open connections at any point in time 40 EOS_CHECKPOINT_FREQUENCY The frequency in seconds of the checkpoint request is sued by the server The time interval between two checkpoints is of importance to the recovery procedure during system restart The default value is set to 600 seconds EOS_SHARED_POOL _SIZE The number of 4K byte pages of the server s buffer pool EOS_LARGE_OBJ_SIZE The size in Kbytes of the extra space the server allocates for large object disk I Os EOS_SHARED_POOL_FILE_PATH The rooted path name of the file that will be used to store the server s buffer pool as well as the extra space allocated for large object I Os This file is memory mapped mmap by the server and the disk daemon during start up The default path is tmp _eos_srv_pool If the file does not exist it will be created automatically EOS_CONTROL_FILE_PATH The rooted path name of the file that will be used to store all con trol structures required by the server s buffer manager This file is memory mapped mmap by the server during start up If the file does not exist it will be created automatically The default path is dev zero EOS_CHECKPOINT_NAME The rooted path name of the checkpoint file EOS_GLOBAL_LOG_NAME The rooted path name of the global log file EOS_PRIVATE_LOG_DIR The rooted path name of the directory used to store private log files All the log records generate
60. s created on the same page the object obj is stored if space is available or in a new page close to it and always in the same area obj is stored On success these three functions return the address of the new object handle On failure they return NULL If data is NULL the object remains uninitialized otherwise it is initialized with the first size bytes pointed by data The hint value is a hint about the potential size of the object being created and it is taken into consideration only if hint gt size EOS will place the object in a page that can accommodate MAX hint size bytes in anticipation of the object growth If no page can accommodate this amount of space EOS switches to a different representation suitable for large objects in way that is invisible to the client The flags value is used for further control of the placement of the new object The flags value is constructed by ORing constants from the following list eosobj NEAR_LAST The new object is appended to the file i e it is placed after the last object in the file This is also the default action when the value of flags is 0 eosobj NEW_PAGE The new object is placed in a brand new page even if some other page can accommodate this object eosobj NOFILL The page in which the new object is stored will not be assigned to any other object that might be created in the future eosobj HDR_ONLY Only the object header remains in the client s pool after the obje
61. s database the function prints an error message and then returns eosexten RETURN This return value instructs EOS to bypass its normal control flow and return immediately with error NULL in this case Thus the call to eosdatabase open that triggered this action returns NULL it is as if EOS could not open this database 5 13 7 Example 2 Fixing C Pointers This example is taken from the implementation of Ode BGLT93 a C based database system that uses EOS as its storage manager The problem encountered during the implementation was that C objects of types that have virtual functions or virtual base classes contain hidden pointers BD G93 pointers that they were not specified by the user In the case of virtual functions the hidden pointer points to a virtual function table that is used to determine which function is to be called In the case of virtual base classes the hidden pointers are used for sharing base classes Str87 Hidden pointers are invalid across program invocations and they need to be fixed We register the hook function fixhidden_ptrs to be execute right after an object fault occurs as follows eosexten insert eosexten OBJECT_FAULT eosexten AFTER fix_hidden_ptrs The hook function fix hidden_ptrs looks as follows int fix_hidden_ptrs eosstat s if has_hidden_ptrs s gt obj gt utag_get s gt obj gt fetch_all fix the pointers return eosexten CONTINUE 33
62. s of the eosareaformat command is the following eosareaformat aname 1 a num s num n num d num e o l It formats a private area on the local machine The EOS server is not contacted Information about this area is kept in the eos areas file of the user executing the command a num The area number to be assigned to the area If no number is specified the system will pick a unique one s num The size of each extent in pages of 4K bytes n num The number of extents in the area d num The maximum number of databases that can be created in this area 12 e It makes the area expandable the area will grow dynamically as more space is needed by appending one extent at a time to the existing ones The area must be a UNIX file to be specified expandable O If the area exists it is re formatted and all its contents are purged The values of the command line arguments that are not specified by the user are taken from the eos formatrc configuration file see section 7 1 4 2 Deleting Areas eosareadelete The eosareadelete command removes an area given either its name or its number eosareadelete aname 1 eosareadelete a num 1 l It removes a private area on the local machine The EOS server is not contacted The record of this area is removed from the eos areas file of the user executing the command aname The rooted path name of the area to be deleted a num The area number of the area
63. t open database s n argv i exit 2 if eostrans begin 0 printf Cannot start a transaction n exit 3 p_array eos_Ref lt eos_Ref lt Part gt gt db gt lookup_object part_array if p_array is_null printf Failed to locate the object n eostrans abort exit 4 Part a_part p_array rand NPARTS traverse a_part int atoi argv 2 1 if eostrans commit printf Transaction commit failed n eostrans abort exit 5 if db gt close printf Cannot close the opened database n exit 6 exit 0 AT 10 Troubleshutting Trying to connect The server was not able to establish the communication link because the port number it uses is busy If this happens the server will re try If the server does not succeed after 5 tries it gives up Solution change the port number the server uses by altering in both the clientre and serverrc configuration files the value of the EOS_SERVER_HOST_PORT The values must be the same in both files and it must be different than the EOS_AREA_HOST_PORT value in the formatre file Note if the above message appears after the message FOS server We are open for business then the problem is with the disk daemon In this case shutdown the server and try again If the problem persists then change the EOS_AREA_HOST_PORT value Cannot create shared memory This may happen when 1 The machine where the server started on do
64. t you do not delete the sign or modify the name of the parameter 2 Set environment variables whose names are identical to the names found in the configuration files For csh or tesh users this can be done as follows setenv name value For korn shell users this can be done as follows name value export name For a given name environment variables are checked first and if no such variable is set the value of the name is taken from the appropriate configuration file For the server there is a third way of initializing the parameters by using command line arguments when the server is invoked Section 6 1 elaborates on this 7 1 Customizing the Area Formatting Procedure formatrc The formation of an area is based on the following environment variables 38 EOS_AREA_EXTENT _SIZE The default extent size of the area being formatted If possible the size of the extent should be set to the number of physically contiguous pages available in the disk device the area resides on In this ways the number of disk seeks required for accessing large objects is minimized EOS_AREA_NEXTENTS The default number of extents of an area being formatted EOS_MAX_DBS_PER_AREA The maximum number of databases that can be created in a given EOS area EOS_AREA_EXPANDABLE This variable specifies whether the area being formatted is expand able i e whether a new extent should be appended to the existing area if more space is requested This variable
65. that is near the page the existing object resides on Clients may also instruct EOS to place the object in a specific storage area and a at the end of a file b in a new page or c not to assign the page on which the object is stored to any other object that is going to be created in the future i e the new object will be the only one in that page The latter may be useful in reducing contention because of locking for frequently accessed pages hot spots 2 1 5 Object Representation and Object Handles Every EOS storage object has an object header attached to it It contains properties of the object such as the object s length whether it is small or large named or unnamed etc Two bytes in the header have no meaning to the storage system and they are available to users to store information about the object To operate on an EOS object a handle to that object must be acquired A handle is a structure that contains among other information the address of the object in the EOS buffer pool When an application requests a handle on an object the appropriate lock for the page the object is stored on is acquired and the page itself is fixed in the buffer pool that is the page will not be replaced or moved in another place until it is unfixed When the object is no longer needed its handle must be released so that the corresponding page in the buffer pool is unfixed The cost of making a handle of a persistent object is at most one
66. they occur and causes the corresponding hooks to be executed e Transactions in a client server environment with the option for experimentation to turn on off the concurrency control logging and recovery components Applications can be linked with the single user version of EOS for accessing private local databases e Concurrency control based on the multigranularity two version two phase locking protocol that allows many readers and one writer to access the same item simultaneously The option to switch to simple 2PL is also provided e Short log files because log records contain only after images of updates e Fast recovery from system failures because only one forward scan over the log is required The restart process can start at any checkpoint taken in the past and stop at any point after that e Non blocking checkpoints that allow active transactions to continue accessing databases while a checkpoint is taken e Configuration files that can be edited by the users to customize and tune EOS performance e Persistent references that are valid across transactions boundaries as well as across databases Objects point to other objects by using persistent references EOS is written in C It can be accessed by programs compiled with any C or C compiler such as the ones distributed by AT amp T Sun GNU and CenterLine Applications that use persistent references must be compiled with a compiler that supports templates The EOS system w
67. to be deleted When an area is deleted by the server the following actions take place 1 Information about the deleted area is erased from the eos areas file of the server account 2 The disk process servicing the deleted area exits 3 The area is removed if it is a UNIX file Removing or reformatting an area dynamically while the server is running is highly discour aged because it is inherently unsafe and it may result in a system failure We suggest to perform such operations when the server is not active because then they can be performed in a safe way Go to the server s account and use the command eosareaformat with the o 1 options to reformat an existing area and eosareadelete command with the 1 to delete an area However if you want to delete or re format an area while the server is running make sure that there is no active transaction using this area 13 5 The EOS Client C Interface The following sections describe the EOS C classes available to programmers The function eos_begin which initializes the internal structures of the EOS storage manager must be invoked before calling any other EOS function 5 1 Object ID class eosoid EOS objects are identified by object ids of type eosoid The data members of the eosoid class are the following eosspid pno the page number the object resides on unsigned ano 14 the area number the page resides in unsigned uno 8 number that approx
68. turns NULL The directory of the new index is an EOS object created in the file pfile The ano specifies the area number in which buckets od this index are allocated If ano is zero the buckets are allocated in the same area in which the directory is stored key_size gives the maximum length of a key val_size gives the size of each value associated with a key and it must be a multiple of four If unique is 0 then multiple values can be associated with the same key Zero length values are allowed only when the index is unique If string is true then the keys are variable size strings init_size specifies the initial number of buckets in the hash hashf and eqf are the user defined hash and key equality functions respectively Their prototypes are typedef unsigned HASH_FUNC const void key typedef int EQ_FUNC const void const void int destroy void destroys an existing extendible hash structure All the entries in the index are destroyed and the directory itself is deleted 5 11 2 Accessing Indexes static eosehash open const eosoid amp oid HASH_FUNC hashf 0 EQ_FUNC eqf 0 opens an extendible hash index whose oid is oid The hashf and eqf are the functions to be used for hashing and comparing for equality index keys Their prototypes are those described in the previous section On success the address of the handle created is returned On failure NULL is returned int close void releases the handle for the index It
69. urns the number of pages the file has int close void closes an open file It returns zero on success non zero on failure The following functions of eosobj are also public members of the eosfile class oid parentoid rootoid utag_get utag_set name name_set name_remove is_named is_root 5 8 File Scan class eosfilescan Visiting objects belonging to a file is done by opening a scan for this file The state of a scan is recorded by a cursor which points to the current object in the file being scanned 23 static eosfilescan open eosfile fh int order AUTO_FWRD const eosoid amp oid eosoid null returns a scan for the file fh or zero on failure The value of order specifies the order in which the object of the file will be scanned It can take be one of the following values eosfilescan AUTO_FWRD automatic scan of the file in forward order starting at object with oid oid or at the very first object if oid is the null eosoid eosfilescan AUTO_BWRD automatic scan of the file in backward order starting at object with oid oid or at the very last object if oid is the null eosoid eosfilescan MANUAL explicit manual movement of the cursor If oid is not the null oid the cursor is position at the object with oid oid eosoid cursor void returns the id of the object pointed by the cursor The eosoid null is returned when the cursor does not point to a valid object or there are no more objects in the file to
70. value returned indicates the number of bits used to distinguish the keys stored in the index const char name void const returns the name if any associated with the index pointed by this or 0 if the index has no name int name_set const char name sets the name of the index to name If the name already exists or an error occurs non zero is returned int name_remove void removes the name of the index It returns zero on success non zero on failure const eosoid amp oid void const returns the object id of the index directory const eosoid amp parentoid void const returns the object id of the file containing the index directory 27 const eosoid amp rootoid void const returns the object id of the database s root file containing the index directory 5 12 Index Scan class eosehashscan EOS provides facilities for accessing all the keys and their accosiated values in an index or all the values associated with a particular key only The state of an index scan is recorded by a cursor which points to the current lt key value gt pair being scanned static eosehashscan open eosehash eh int order AUTO_FWRD const void key 0 opens a scan for the index pointed by eh It returns 0 on failure If the value of key is not NULL then the scan is opened for this particular key order specifies the order in which the lt key value gt pairs of the index will be scanned It can take one of the following values eosehashsc
71. will appear 37 7 EOS Customization The client and the server modules of FOS as well as the one that formats an area use a number of environment variables to perform their task EOS provides three installation programs that set up default values for all these variables so users that do not want to customize EOS or they are not concerned with performance need only change few things to set up their environment The default values of these variables are stored in three configuration files named formatrc clientre and serverrc under the HOME eos directory of the user making the installation The following are the three programs that install the default values of the environment variables used by EOS e eosformatenv creates and initializes the configuration file formatrc this file is used whenever a new area is formatted with the eosareaformat command e eosclientenv creates and initializes the configuration file clientrc this file is used by the applications linked with the private o or client o object module of EOS e eosserverenv creates and initializes the configuration file serverrc this file is used by the EOS server The configuration files contain name value pairs one per line with the equal sign separating the value from the name There are two ways to change these default values 1 Use an editor to open the configuration file and locate the parameter whose value is going to be updated update the value making sure tha

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