NOTE You cannot issue CREATE STORAGE AREA as an independent statement. It is a clause allowed only as part of a CREATE DATABASE or IMPORT statement. You can also create a storage area using the ADD STORAGE AREA clause of the ALTER DATABASE statement. Creates additional storage areas in a multifile database. Storage areas are data and snapshot files that are associated with particular tables in a multifile database. A CREATE STORAGE AREA clause specifies the names for the storage area files and determines their physical characteristics. Subsequent CREATE STORAGE MAP statements associate the storage area with particular tables in the database.
1 – Environment
You can use the CREATE STORAGE AREA clause only within a CREATE DATABASE or IMPORT statement.
2 – Format
(B)0[m[1;4mCREATE[m[1m [1;4mSTORAGE[m[1m [1;4mAREA[m[1m qwq> <area-name> qwqwqqqqqqqqqqqqqqqqqqqqqqqqqwk [m [1m mq> [1;4mRDB$SYSTEM[m[1m qqj mq> [1;4mFILENAME[m[1m <file-spec> qjx [m [1m lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj [m [1m mwqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqwqwq> [m [1m mqwqwq> storage-area-params-1 qu x [m [1m x mq> storage-area-params-2 qj x [m [1m mqqqqqqqqqqqqqqq <qqqqqqqqqqqqqj [m [1m [m (B)0[m[1mstorage-area-params-1 = [m [1m [m [1mqqwq> [1;4mALLOCATION[m[1m IS qqq> <number-pages> qq> PAGES qqqqqwq>[m [1m tq> [1;4mCACHE[m[1m [1;4mUSING[m[1m <row-cache-name> qqqqqqqqqqqqqqqqqqqqu [m [1m tq> [1;4mNO[m[1m ROW [1;4mCACHE[m[1m qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu [m [1m tq> extent-params qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu [m [1m tq> [1;4mINTERVAL[m[1m IS qq> <number-data-pages> qqqqqqqqqqqqqu [m [1m tq> [1;4mLOCKING[m[1m IS qqwq> [1;4mROW[m[1m qqwqq> LEVEL qqqqqqqqqqqqqqqu [m [1m x mq> [1;4mPAGE[m[1m qj x [m [1m tq> [1;4mPAGE[m[1m [1;4mFORMAT[m[1m IS wq> [1;4mUNIFORM[m[1m qwqqqqqqqqqqqqqqqqqqqqu [m [1m x mq> [1;4mMIXED[m[1m qqqj x [m [1m mq> [1;4mPAGE[m[1m [1;4mSIZE[m[1m IS qqqq> <page-blocks> qq> BLOCKS qqqqqj [m [1m [m (B)0[m[1mextent-params = [m [1m [m [1mqqwq> [1;4mEXTENT[m[1m IS qwq> [1;4mENABLED[m[1m qqqqqqqqqqqqqqqqqqqwwqq> [m [1m x tq> [1;4mDISABLED[m[1m qqqqqqqqqqqqqqqqqqux [m [1m x tq> <extent-pages> qq> PAGES qqux [m [1m x mq> (extension-options) qqqqqqqjx [m [1m mqqqqqqqqqqqqqqqqqqqqq<qqqqqqqqqqqqqqqqqqqqqqqqj [m [1m [m (B)0[m[1mextension-options = [m [1m [m [1mqqq> [1;4mMINIMUM[m[1m OF <min-pages> PAGES, qqk [m [1mlqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj [m [1mmqq> [1;4mMAXIMUM[m[1m OF <max-pages> PAGES, qqk [m [1mlqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj [m [1mmqq> [1;4mPERCENT[m[1m [1;4mGROWTH[m[1m IS <growth> qqqqqqq> [m [1m [m (B)0[m[1mstorage-area-params-2 = [m [1m [m [1mqqwq> [1;4mCHECKSUM[m[1m CALCULATION IS qqqqqqqqqqqwqqwq> [1;4mENABLED[m[1m qqwqwq>[m [1m tq> [1;4mSNAPSHOT[m[1m [1;4mCHECKSUM[m[1m CALCULATION IS qqj mq> [1;4mDISABLED[m[1m qj x [m [1m tq> [1;4mSNAPSHOT[m[1m [1;4mALLOCATION[m[1m IS qq> <snp-pages> qqqq> PAGES qqqu [m [1m tq> [1;4mSNAPSHOT[m[1m [1;4mEXTENT[m[1m IS qwq> <extent-pages> qqqq> PAGES qqwu [m [1m x mq> (extension-options) qqqqqqqqqjx [m [1m tq> [1;4mSNAPSHOT[m[1m [1;4mFILENAME[m[1m qq> <file-spec> qqqqqqqqqqqqqqqqqqqqu [m [1m tq> [1;4mTHRESHOLDS[m[1m ARE ( <val1> wqqqqqqqqqqqqqqqqqqqqqqqw> ) qu [m [1m x m> ,<val2> qwqqqqqqqqqqwj x [m [1m x m> ,<val3> j x [m [1m mq[mqqqqqqqqqqqqqqqqqqqqqqqqqqqqq[1m<qqqqqqqqqqqqqqqqqqqqqqqqqqj [m [1m [m
3 – Arguments
3.1 – ALLOCATION_PAGES
Syntax option: ALLOCATION IS number-pages PAGES The number of database pages initially allocated to the storage area. Rdb will automatically extend this allocation to account for internal structure pages, such as SPAM (spage management) pages. For example, an allocation of 25 will be increased to 27 as shown in this example: SQL> alter database filename MF_PERSONNEL cont> add storage area DOC_EXAMPLE cont> page format is uniform cont> allocation 25; SQL> attach 'filename MF_PERSONNEL'; SQL> show storage area DOC_EXAMPLE DOC_EXAMPLE Access is: Read write Page Format: Uniform Page Size: 2 blocks Area File: USER_DISK:[DOC.DATABASES]DOC_EXAMPLE.RDA;1 Area Allocation: 27 pages Extent: Enabled Area Extent Minimum: 99 pages Area Extent Maximum: 9999 pages Area Extent Percent: 20 percent Snapshot File: USER_DISK:[DOC.DATABASES]DOC_EXAMPLE.SNP;1 Snapshot Allocation: 100 pages Snapshot Extent Minimum: 99 pages Snapshot Extent Maximum: 9999 pages Snapshot Extent Percent: 20 percent Locking is Row Level No Cache Associated with Storage Area No database objects use Storage Area DOC_EXAMPLE
3.2 – CACHE USING row cache name
Assigns the named row cache to the specified storage area. All rows stored in this area, whether they consist of table data, segmented string data, or special rows such as index nodes, are cached if those rows fit in the cache. If the row cache does not exist, you must create the row cache before terminating the CREATE DATABASE statement. For example: SQL> CREATE DATABASE FILENAME test_db cont> ROW CACHE IS ENABLED cont> CREATE STORAGE AREA area1 cont> CACHE USING test1 cont> CREATE CACHE test1 cont> CACHE SIZE IS 100 ROWS cont> ROW LENGTH IS 200 BYTES; Only one row cache is allowed for each storage area. NO ROW CACHE is the default for a storage area.
3.3 – CHECKSUM_CALCULATION
Syntax options: CHECKSUM CALCULATION | SNAPSHOT CHECKSUM CALCULATION This option allows you to enable or disable calculations of page checksums when pages are read from or written to the storage or snapshot area files. The default is ENABLED. NOTE Oracle Corporation recommends that you leave checksum calculations enabled; which is the default. With current technology, it is possible that errors may occur that the checksum calculation can detect but that may not be detected by either the hardware, firmware, or software. Unexpected application results and database corruption may occur if corrupt pages exist in memory or on disk but are not detected. Oracle Corporation recommends performing checksum calculations, except in the following specific circumstances: o Your application is stable and has run without errors on the current hardware and software configuration for an extended period of time. o You have reached maximum CPU utilization in your current configuration. Actual CPU utilization by the checksum calculation depends primarily on the size of the database pages in your database. The larger the database page, the more noticeable the CPU usage by the checksum calculation may become. NOTE Oracle Corporation recommends that you carefully evaluate the trade-off between reducing CPU usage by the checksum calculation and the potential for loss of database integrity if checksum calculations are disabled. Oracle Rdb allows you to disable and, subsequently, re-enable checksum calculation without error. However, once checksum calculations have been disabled, corrupt pages may not be detected even if checksum calculations are subsequently re- enabled.
3.4 – EXTENT
Syntax options: EXTENT ENABLED | EXTENT DISABLED Enables or disables extents. Extents are ENABLED by default. You may encounter performance problems when creating hashed indexes in storage areas with the mixed page format if the storage area was created specifying the incorrect size for the area and if extents are enabled. By disabling extents, this problem can be diagnosed early and corrected to improve performance.
3.5 – EXTENT_IS
Syntax options: EXTENT IS extent-pages PAGES | EXTENT IS (extension-options) Specifies the number of pages of each storage area file extent. See also the description under the SNAPSHOT EXTENT argument.
3.6 – FILENAME file spec
Provides an explicit file specification for storage area files. The CREATE STORAGE AREA clause creates two files: a storage area file with a file extension of .rda, and a snapshot file with a file extension of .snp. If you omit the FILENAME argument, the file specification takes the following defaults: o Device: the current device for the process o Directory: the current directory for the process o File name: the name specified for the storage area Neither the file specification for the storage area nor the snapshot file may contain a node specification. The file specification is used for both the storage area and snapshot files that comprise the storage area (unless you use the SNAPSHOT FILENAME argument to specify a different file for the snapshot file). Because the CREATE STORAGE AREA clause can create two files with different file extensions, do not specify a file extension with the file specification. You may use a logical name for all or part of a file specification. One benefit of a multifile database is that its files can reside on more than one disk. If you want storage area files to reside on another disk, you must specify the FILENAME argument with a full file specification. However, you may choose to create a multifile database even if your main purpose in creating the storage area is not to distribute storage area files across more than one disk. For instance, a multifile database enables you to: o Take advantage of hashed indexes. Hashed indexes require a storage area with mixed page format and cannot be stored in the RDB$SYSTEM storage area. o Set attributes such as page size to better correspond with tables that will be stored in the storage area.
3.7 – INTERVAL
Syntax options: INTERVAL IS number-data-pages Specifies the number of data pages between SPAM pages in the storage area file, and thus the maximum number of data pages each SPAM page manages. The default, and also the minimum interval, is 216 data pages. The first page of each storage area is a SPAM page. The interval you specify determines where subsequent SPAM pages are to be inserted if there are enough data pages in the storage file to require more SPAM pages. You cannot specify the INTERVAL storage area parameter unless you also explicitly specify PAGE FORMAT IS MIXED. Oracle Rdb calculates the maximum INTERVAL size based on the number of blocks per page, and returns an error message if you exceed this value. For example, when the page size is 2 blocks, the maximum INTERVAL is 4008 pages. If you try to create a storage area with the INTERVAL set to 4009, Oracle Rdb returns the following error message: %RDB-E-BAD_DPB_CONTENT, invalid database parameters in the database parameter block (DPB) -RDMS-F-SPIMAX, spam interval of 4009 is more than the Rdb maximum of 4008 -RDMS-F-AREA_NAME, area NEW For more information about setting space area management parameters, see the Oracle Rdb Guide to Database Maintenance.
3.8 – LOCKING level
Syntax options: LOCKING IS ROW LEVEL | LOCKING IS PAGE LEVEL Specifies if locking is at the page or row level for the storage area. This clause provides an alternative to requesting locks on records. Specifying a lock level when you create a storage area overrides the database default lock level. The default is ROW LEVEL. When many records are accessed in the same area and on the same page, the LOCKING IS PAGE LEVEL clause reduces the number of lock operations performed to process a transaction; however, this is at the expense of reduced concurrency because these pages' locks are held until COMMIT/ROLLBACK. Transactions that benefit most with page-level locking are of short duration and also access several database records on the same page. However, to guarantee consistency of the data in the absence of row locking these page level locks must be held until the transaction ends with COMMIT or ROLLBACK. Use the LOCKING IS ROW LEVEL if transactions are long in duration and lock many rows. The LOCKING IS PAGE LEVEL clause causes fewer blocking ASTs and provides better response time and utilization of system resources. However, there is a higher contention for pages and increased potential for deadlocks and long transactions may use excessive locks. Page-level locking is never applied to RDB$SYSTEM or the DEFAULT storage-area, either implicitly or explicitly, because the locking protocol can stall metadata users. You cannot specify page-level locking on single-file databases.
3.9 – MAXIMUM_PAGES
Syntax options: MAXIMUM OF max-pages PAGES Specifies the maximum number of pages of each extent. The default is 9,999 pages.
3.10 – MINIMUM_PAGES
Syntax options: MINIMUM OF min-pages PAGES Specifies the minimum number of pages of each extent. The default is 99 pages.
3.11 – NO_ROW_CACHE
Specifies that a row cache is not assigned to the specified storage area in the database. You cannot specify the NO ROW CACHE clause if you specify the CACHE USING clause. Alter the storage area and name a row cache with the CACHE USING clause to assign a row cache to the storage area or to override the database default. Only one row cache is allowed for each storage area.
3.12 – PAGE_FORMAT
Syntax options: PAGE FORMAT IS UNIFORM | PAGE FORMAT IS MIXED Specifies the on-disk structure for the storage area. o The default is PAGE FORMAT IS UNIFORM. A storage area with uniform page format is a file that is divided into groups of n pages, called clumps, where n equals the buffer size divided by the page size. Both buffer size and page size are user specified values. By default, the buffer size is 6 blocks, and the page size is 1024 bytes or 2 blocks long, resulting in clumps of three pages. The PAGE FORMAT IS UNIFORM argument creates a storage area file that is divided into clumps. A set of clumps forms a logical area that can contain rows from a single table or index only. Uniform page format storage areas generally give the best performance if the tables in the storage area are likely to be subject to a wide range of queries. o The PAGE FORMAT IS MIXED argument creates a storage area with a format that allows rows from more than one table to reside on or near a particular page of the storage area file. This is useful for storing related rows from different tables on the same page of the data file. For storage areas subject to repeated queries that retrieve those related rows, a mixed page format can greatly reduce input/output overhead if the mix of rows on the page is carefully controlled. However, mixed page format storage areas degrade performance if the mix of rows on the page is not suited for the queries made against the storage area. For more information on the relative advantages and disadvantages of uniform and mixed storage areas, see the Oracle Rdb Guide to Database Maintenance.
3.13 – PAGE SIZE blocks
Syntax options: PAGE SIZE IS page-blocks BLOCKS The size in blocks of each data page in the storage area. Page size is allocated in 512-byte blocks. The default is 2 blocks (1024 bytes). If your largest row is larger than approximately 950 bytes, allocate more blocks per page to prevent fragmented rows. If you specify a page size larger than the buffer size, an error message is returned.
3.14 – PERCENT_GROWTH
Syntax options: PERCENT GROWTH IS growth Specifies the percent growth of each extent. The default is 20 percent growth.
3.15 – SNAPSHOT_ALLOCATION
Syntax options: SNAPSHOT ALLOCATION IS snp-pages PAGES Specifies the number of pages allocated for the snapshot file. The default is 100 pages.
3.16 – SNAPSHOT_EXTENT
Syntax options: SNAPSHOT EXTENT IS extent-pages | SNAPSHOT EXTENT IS (extension- options) Specifies the number of pages of each snapshot or storage area file extent. The default extent for storage area files is 100 pages. Specify a number of pages for simple control over the extension. For greater control, and particularly for multivolume databases, use the MIN, MAX, and PERCENT GROWTH extension options instead. If you use the MIN, MAX, and PERCENT GROWTH parameters, you must enclose them in parentheses.
3.17 – SNAPSHOT_FILENAME
Syntax options: SNAPSHOT FILENAME file-spec Provides a separate file specification for the snapshot file. The SNAPSHOT FILENAME argument can only be specified with multifile databases. This argument lets you specify a different file name, device, or directory for the snapshot file created by the CREATE STORAGE AREA clause. Do not specify a file extension other than .snp to the file specification. Oracle Rdb assigns the extension .snp to the file specification, even if you specify an alternate extension. If you omit the SNAPSHOT FILENAME argument, the snapshot file gets the same device, directory, and file name as the storage area file.
3.18 – STORAGE_AREA
Specifies the name of the storage area you want to create. The name cannot be the same as any other storage area definition in the database.
3.19 – STORAGE_AREA_RDB$SYSTEM
Specifies that you want the CREATE STORAGE AREA clause to override the default characteristics for the main storage area, RDB$SYSTEM, in a new database. The RDB$SYSTEM storage area contains database system tables and indices. If an alternate DEFAULT STORAGE AREA is not assigned then this area may also contain unmapped user tables and indices.
3.20 – THRESHOLDS values
Syntax options: THRESHOLDS ARE ( val1 [,val2 [,val3] ] ) Specifies one, two, or three threshold values for mixed format pages. The threshold values represent a fullness percentage on a data page and establish three possible ranges of guaranteed free space on the data pages. When a data page reaches the percentage defined by a given threshold value, the space area management (SPAM) entry for the data page is updated to reflect the new fullness percentage and its remaining free space. The default threshold values for mixed areas, if not specified, are (70,85,95), which indicates that the nominal record size should be used for SPAM threshold calculations. Oracle Rdb never stores a record on a page at the third threshold. The value you set for the highest threshold can be used to reserve space on the page for future record growth. When only val1 is specified, this is equivalent to (val1, 100, 100). When val1 and val2 are specified, this is equivalent to (val1, val2, 100). The trailing, unspecified thresholds default to 100 percent. For example, THRESHOLDS ARE (40) would appear as (40, 100, 100). You cannot specify the THRESHOLDS storage area parameter unless you also explicitly specify PAGE FORMAT IS MIXED. For more information about setting space area management parameters, see the Oracle Rdb Guide to Database Maintenance.
4 – Examples
Example 1: Defining a multifile database This example shows the definition of a database and storage areas for a multifile database. SQL> -- Note that there is no semicolon before SQL> -- the first CREATE STORAGE AREA clause. SQL> CREATE DATABASE ALIAS MULTIFILE_EXAMPLE cont> FILENAME 'DB_DATA01:[DB.DATA]MULTIFILE_EXAMPLE' cont> CREATE STORAGE AREA EMPID_LOW cont> FILENAME 'DB_DATA02:[DB.DATA]EMPID_LOW' cont> ALLOCATION IS 10 PAGES cont> -- Notice that the snapshot file resides on a cont> -- different disk than the storage area file. This cont> -- strategy reduces disk input/output bottlenecks: cont> SNAPSHOT FILENAME 'DB_SNAP03:[DB.SNAP]EMPID_LOW' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> CREATE STORAGE AREA EMPID_MID cont> FILENAME 'DB_DATA04:EMPID_MID' cont> ALLOCATION IS 10 PAGES cont> SNAPSHOT FILENAME 'DB_SNAP05:[DB.SNAP]EMPID_MID' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> CREATE STORAGE AREA EMPID_OVER cont> FILENAME 'DB_DATA06:[DB.DATA]EMPID_OVER' cont> ALLOCATION IS 10 PAGES cont> SNAPSHOT FILENAME 'DB_SNAP07:[DB.SNAP]EMPID_OVER' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> CREATE STORAGE AREA HISTORIES cont> FILENAME 'DB_DATA02:[DB.DATA]HISTORIES' cont> ALLOCATION IS 10 PAGES cont> SNAPSHOT FILENAME 'DB_SNAP03:[DB.SNAP]HISTORIES' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> CREATE STORAGE AREA CODES cont> FILENAME 'DB_DATA04:[DB.DATA]CODES' cont> ALLOCATION IS 10 PAGES cont> SNAPSHOT FILENAME 'DB_SNAP05:[DB.SNAP]CODES' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> CREATE STORAGE AREA EMP_INFO cont> FILENAME 'DB_DATA08:[DB.DATA]EMP_INFO' cont> ALLOCATION IS 10 PAGES cont> SNAPSHOT FILENAME 'DB_SNAP09:[DB.SNAP]EMP_INFO' cont> SNAPSHOT ALLOCATION IS 10 PAGES cont> -- cont> -- End the CREATE DATABASE statement: cont> ; Example 2: This example shows how to set page-level and row-level locking on storage areas from both the database level and from the storage area level. SQL> CREATE DATABASE FILENAME sample cont> LOCKING IS PAGE LEVEL cont> -- cont> -- All storage areas will default to page-level locking unless cont> -- explicitly set to row-level locking. cont> -- cont> CREATE STORAGE AREA RDB$SYSTEM cont> FILENAME sample_system cont> -- cont> -- You cannot specify page-level locking on RDB$SYSTEM. RDB$SYSTEM cont> -- always defaults to row-level locking. cont> -- cont> CREATE STORAGE AREA HASH_AREA cont> FILENAME sample_hash cont> PAGE FORMAT IS MIXED cont> -- cont> -- HASH_AREA defaultS to page-level locking. cont> -- cont> CREATE STORAGE AREA DATA_AREA cont> FILENAME sample_data cont> LOCKING IS ROW LEVEL cont> -- cont> -- DATA_AREA is explicitly set to row-level locking. cont> -- cont> ; SQL> SHOW STORAGE AREAS (ATTRIBUTES) * Storage Areas in database with filename sample RDB$SYSTEM List storage area. Access is: Read write Page Format: Uniform Page Size: 2 blocks . . . Extent : Enabled Locking is Row Level HASH_AREA Access is: Read write Page Format: Mixed Page Size: 2 blocks . . . Extent : Enabled Locking is Page Level DATA_AREA Access is: Read write Page Format: Uniform Page Size: 2 blocks . . . Extent : Enabled Locking is Row Level See the SHOW statement for information on the SHOW STORAGE AREAS statement. Example 3: Creating and assigning a row cache to a storage area SQL> create database cont> filename SAMPLE_DB cont> reserve 2 cache slots cont> row cache is enabled cont> default storage area is AREA1 cont> create cache CACHE1 cont> cache size is 1000 rows cont> row length is 1000 bytes cont> create storage area AREA1 cont> cache using CACHE1 cont> ; SQL> show cache CACHE1 CACHE1 Cache Size: 1000 rows Row Length: 1000 bytes Row Replacement: Enabled Shared Memory: Process Large Memory: Disabled Window Count: 100 Working Set Count: 10 Reserved Rows: 20 Allocation: 100 blocks Extent: 100 blocks SQL> show storage area AREA1 AREA1 Access is: Read write Page Format: Uniform Page Size: 2 blocks Area File: USER_DISK:[DOC.DATABASES]AREA1.RDA;1 Area Allocation: 702 pages Extent: Enabled Area Extent Minimum: 99 pages Area Extent Maximum: 9999 pages Area Extent Percent: 20 percent Snapshot File: USER_DISK:[DOC.DATABASES]AREA1.SNP;1 Snapshot Allocation: 100 pages Snapshot Extent Minimum: 99 pages Snapshot Extent Maximum: 9999 pages Snapshot Extent Percent: 20 percent Locking is Row Level Using Cache CACHE1 Database objects using Storage Area AREA1: Usage Object Name Map / Partition ---------------- ------------------------------- ------------------------------- Default Area