Oracle Table 创建参数 说明

先看一个oracle 10g 下table 创建SQL,都是默认值：

CREATE TABLE SYS.QS

(

  USERNAME  VARCHAR2(30 BYTE)                   NOT NULL,

  USER_ID   NUMBER                              NOT NULL,

  CREATED   DATE                                NOT NULL

)

TABLESPACE SYSTEM

PCTUSED    40

PCTFREE    10

INITRANS   1

MAXTRANS   255

STORAGE    (

            INITIAL          64K

            MINEXTENTS       1

            MAXEXTENTS       UNLIMITED

            PCTINCREASE      0

            FREELISTS        1

            FREELIST GROUPS  1

            BUFFER_POOL      DEFAULT

           )

LOGGING

NOCOMPRESS

NOCACHE

NOPARALLEL

MONITORING;

 

       对于 数据字典管理（Dictionary managed）和 本地化管理（Local Managed）的表空间，他们的参数是不同的， 在Local Managed 模式下，的autoallocate和 uniform类型不同，参数也会不同。 这里使用的是local managed autoallocate类型的表空间。

       Oracle 表空间 创建参数 说明

       http://blog.csdn.net/xujinyang/article/details/6829309

 

官网链接：

storage_clause

http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/clauses009.htm#SQLRF30013

 

CREATE TABLE

http://download.oracle.com/docs/cd/E11882_01/server.112/e17118/statements_7002.htm#SQLRF01402

 

       表空间(tableSpace) 段(segment) 盘区(extent) 块(block) 关系

       http://blog.csdn.net/xujinyang/article/details/6829910

 

 

一.  Storage 参数说明

 

1. INITIAL

       Specify the size of the first extent of the object. Oracle allocates space for this extent when you create the schema object. Refer to size_clause for information on that clause.

       In locally managed tablespaces, Oracle uses the value of INITIAL, in conjunction with the type of local management—AUTOALLOCATE or UNIFORM—and the values of MINEXTENTS, NEXT and PCTINCREASE, to determine the initial size of the segment.

（1）.      With AUTOALLOCATE extent management, Oracle uses the INITIAL setting to optimize the number of extents allocated. Extents of 64K, 1M, 8M, and 64M can be allocated. During segment creation, the system chooses the greatest of these four sizes that is equal to or smaller than INITIAL, and allocates as many extents of that size as are needed to reach or exceed the INITIAL setting. For example, if you set INITIAL to 4M, then the database creates four 1M extents. But if you set INITIAL to 14M, then the database creates two 8M extents, which exceeds the INITIAL setting, rather than creating the less optimal one 8M extent plus six 1M extents.

（2）.      For UNIFORM extent management, the number of extents is determined from initial segment size and the uniform extent size specified at tablespace creation time. For example, in a uniform locally managed tablespace with 1M extents, if you specify an INITIAL value of 5M, then Oracle creates five 1M extents.

 

Consider this comparison: With AUTOALLOCATE, if you set INITAL to 72K, then the initial segment size will be 128K (greater than INITIAL). The database cannot allocate an extent smaller than 64K, so it must allocate two 64K extents. If you set INITIAL to 72K with a UNIFORM extent size of 24K, then the database will allocate three 24K extents to equal 72K.

 

       In dictionary managed tablespaces, the default initial extent size is 5 blocks, and all subsequent extents are rounded to 5 blocks. If MINIMUM EXTENT was specified at tablespace creation time, then the extent sizes are rounded to the value of MINIMUM EXTENT.

       -- 自Oracle 9i 以后，推荐使用本地管理的表空间，不建议使用字典管理的表空间。

       Restriction on INITIAL You cannot specify INITIAL in an ALTER statement.

 

2.  MINEXTENTS

       （1）In locally managed tablespaces, Oracle Database uses the value of MINEXTENTS in conjunction with PCTINCREASE, INITIAL and NEXT to determine the initial segment size.

       （2）In dictionary-managed tablespaces, specify the total number of extents to allocate when the object is created. The default and minimum value is 1,meaning that Oracle allocates only the initial extent, except for rollback segments, for which the default and minimum value is 2. The maximum value depends on your operating system.

（1）.      In a locally managed tablespace, MINEXTENTS is used to compute the initial amount of space allocated, which is equal to INITIAL * MINEXTENTS. Thereafter this value is set to 1, which is reflected in the DBA_SEGMENTS view.

（2）.      In a dictionary-managed tablespace, MINEXTENTS is simply the minimum number of extents that must be allocated to the segment.

 

       If the MINEXTENTS value is greater than 1, then Oracle calculates the size of subsequent extents based on the values of the INITIAL, NEXT, and PCTINCREASE storage parameters.

 

       When changing the value of MINEXTENTS by specifying it in an ALTER statement, you can reduce the value from its current value, but you cannot increase it.Resetting MINEXTENTS to a smaller value might be useful, for example, before a TRUNCATE ... DROP STORAGE statement, if you want to ensure that the segment will maintain a minimum number of extents after the TRUNCATE operation.

 

Restrictions on MINEXTENTS 

The MINEXTENTS storage parameter is subject to the following restrictions:

（1）.      MINEXTENTS is not applicable at the tablespace level.

（2）.      You cannot change the value of MINEXTENTS in an ALTER statement or for an object that resides in a locally managed tablespace.

 

3. MAXEXTENTS

      This storage parameter is valid only for objects in dictionary-managed tablespaces. Specify the total number of extents, including the first, that Oracle can allocate for the object. The minimum value is 1 except for rollback segments, which always have a minimum of 2. The default value depends on your data block size.

Restriction on MAXEXTENTS 

       MAXEXTENTS is ignored for objects residing in a locally managed tablespace, unless the value of ALLOCATION_TYPE is USER for the tablespace in the DBA_TABLESPACES data dictionary view.

--该参数在local managed tablespace 是忽略的。

 

UNLIMITED 

       Specify UNLIMITED if you want extents to be allocated automatically as needed. Oracle recommends this setting as a way to minimize fragmentation.

       Do not use this clause for rollback segments. Doing so allows the possibility that long-running rogue DML transactions will continue to create new extents until a disk is full.

 

Caution:

       A rollback segment that you create without specifying the storage_clause has the same storage parameters as the tablespace in which the rollback segment is created. Thus, if you create a tablespace with MAXEXTENTS UNLIMITED, then the rollback segment will have this same default.

 

4.  PCTINCREASE

       （1）In locally managed tablespaces, Oracle Database uses the value of PCTINCREASE during segment creation to determine the initial segment size andignores this parameter during subsequent space allocation.

       （2）In dictionary-managed tablespaces, specify the percent by which the third and subsequent extents grow over the preceding extent. The default value is 50, meaning that each subsequent extent is 50% larger than the preceding extent. The minimum value is 0, meaning all extents after the first are the same size.The maximum value depends on your operating system. Oracle rounds the calculated size of each new extent to the nearest multiple of the data block size. If you change the value of the PCTINCREASE parameter by specifying it in an ALTER statement, then Oracle calculates the size of the next extent using this new value and the size of the most recently allocated extent.

 

Restriction on PCTINCREASE

       You cannot specify PCTINCREASE for rollback segments. Rollback segments always have a PCTINCREASE value of 0.

 

5. FREELISTS

       （1）In tablespaces with manual segment-space management, Oracle Database uses the FREELISTS storage parameter to improve performance of space management in OLTP systems by increasing the number of insert points in the segment.

       （2）In tablespaces with automatic segment-space management, this parameter is ignored, because the database adapts to varying workload.

 

       In tablespaces with manual segment-space management, for objects other than tablespaces and rollback segments, specify the number of free lists for each of the free list groups for the table, partition, cluster, or index. The default and minimum value for this parameter is 1, meaning that each free list group contains one free list. The maximum value of this parameter depends on the data block size. If you specify a FREELISTS value that is too large, then Oracle returns an error indicating the maximum value.

 

       This clause is not valid or useful if you have specified the SECUREFILE parameter of LOB_parameters. If you specify both the SECUREFILE parameter and FREELISTS, then the database silently ignores the FREELISTS specification.

 

Restriction on FREELISTS 

       You can specify FREELISTS in the storage_clause of any statement except when creating or altering a tablespace or rollback segment.

 

6. FREELIST GROUPS

       （1）In tablespaces with manual segment-space management, Oracle Database uses the value of this storage parameter to statically partition the segment free space in an Oracle Real Application Clusters environment. This partitioning improves the performance of space allocation and deallocation by avoiding inter instance transfer of segment metadata. In tablespaces with automatic segment-space management, this parameter is ignored, because Oracle dynamically adapts to inter instance workload.

       （2）In tablespaces with manual segment-space management, specify the number of groups of free lists for the database object you are creating. The default and minimum value for this parameter is 1. Oracle uses the instance number of Oracle Real Application Clusters (Oracle RAC) instances to map each instance to one free list group.

 

Each free list group uses one database block. Therefore:

（1）.      If you do not specify a large enough value for INITIAL to cover the minimum value plus one data block for each free list group, then Oracle increases the value of INITIAL the necessary amount.

（2）.      If you are creating an object in a uniform locally managed tablespace, and the extent size is not large enough to accommodate the number of freelist groups, then the create operation will fail.

 

       This clause is not valid or useful if you have specified the SECUREFILE parameter of LOB_parameters. If you specify both the SECUREFILE parameter and FREELIST GROUPS, then the database silently ignores the FREELIST GROUPS specification.

 

Restriction on FREELIST GROUPS 

       You can specify the FREELIST GROUPS parameter only in CREATE TABLE, CREATE CLUSTER, CREATE MATERIALIZED VIEW, CREATE MATERIALIZED VIEW LOG, and CREATE INDEX statements.

 

7. BUFFER_POOL

       The BUFFER_POOL clause lets you specify a default buffer pool or cache for a schema object. All blocks for the object are stored in the specified cache.

（1）.      If you define a buffer pool for a partitioned table or index, then the partitions inherit the buffer pool from the table or index definition unless overridden by a partition-level definition.

（2）.      For an index-organized table, you can specify a buffer pool separately for the index segment and the overflow segment.

 

Restrictions on the BUFFER_POOL Parameter 

BUFFER_POOL is subject to the following restrictions:

（1）.      You cannot specify this clause for a cluster table. However, you can specify it for a cluster.

（2）.      You cannot specify this clause for a tablespace or a rollback segment.

 

KEEP 

       Specify KEEP to put blocks from the segment into the KEEP buffer pool. Maintaining an appropriately sized KEEP buffer pool lets Oracle retain the schema object in memory to avoid I/O operations. KEEP takes precedence over any NOCACHE clause you specify for a table, cluster, materialized view, or materialized view log.

 

RECYCLE 

       Specify RECYCLE to put blocks from the segment into the RECYCLE pool. An appropriately sized RECYCLE pool reduces the number of objects whose default pool is the RECYCLE pool from taking up unnecessary cache space.

DEFAULT 

       Specify DEFAULT to indicate the default buffer pool. This is the default for objects not assigned to KEEP or RECYCLE.

 

 

二. 其他参数说明

1.  Pctfree： 默认值是 10，如果数据块的使用率高于pctfree的值，则该数据块从freelist中移出。

2. Pctused ：默认值是40，如果数据块的使用率小于pctused的值，则该数据块重新加入到fresslist中。Pctfree, Pctused是互相消涨的, 其和不能超过100

3. Initrans ： 默认值1，该参数表示在单一块中最初活动的交易事务数。

4. Maxtrans ：默认值是255，表示在单一块中最大交易事务数。

 

5. logging_clause

       Specify whether the creation of the table and of any indexes required because of constraints, partition, or LOB storage characteristics will be logged in the redo log file (LOGGING) or not (NOLOGGING).The logging attribute of the table is independent of that of its indexes.

       This attribute also specifies whether subsequent direct loader (SQL*Loader) and direct-path INSERT operations against the table, partition, or LOB storage are logged (LOGGING) or not logged (NOLOGGING).

 

6. table_compression

       The table_compression clause is valid only for heap-organized tables. Use this clause to instruct the database whether to compress data segments to reduce disk use. The COMPRESS keyword enables table compression. The NOCOMPRESS keyword disables table compression. NOCOMPRESS is the default.

       （1）When you enable table compression by specifying either COMPRESS or COMPRESS BASIC, you enable basic table compression. Oracle Database attempts to compress data during direct-path INSERT operations when it is productive to do so. The original import utility (imp) does not support direct-path INSERT, and therefore cannot import data in a compressed format.

       Tables with COMPRESS or COMPRESS BASIC use a PCTFREE value of 0 to maximize compression, unless you explicitly set a value for PCTFREE in the physical_attributes_clause.

       In earlier releases, this type of compression was called DSS table compression and was enabled using COMPRESS FOR DIRECT_LOAD OPERATIONS. This syntax has been deprecated.

       （2）When you enable table compression by specifying COMPRESS FOR OLTP, you enable OLTP table compression. Oracle Database compresses data during all DML operations on the table. This form of compression is recommended for OLTP environments.

       Tables with COMPRESS FOR OLTP or NOCOMPRESS use the PCTFREE default value of 10, to maximize compress while still allowing for some future DML changes to the data, unless you override this default explicitly.

       In earlier releases, OLTP table compression was enabled using COMPRESS FOR ALL OPERATIONS. This syntax has been deprecated.

       （3）When you specify COMPRESS FOR QUERY or COMPRESS FOR ARCHIVE, you enable hybrid columnar compression. With hybrid columnar compression, data can be compressed during bulk load operations. During the load process, data is transformed into a column-oriented format and then compressed. Oracle Database uses a compression algorithm appropriate for the level you specify. In general, the higher the level, the greater the compression ratio. Hybrid columnar compression can result in higher compression ratios, at a greater CPU cost. Therefore, this form of compression is recommended for data that is not frequently updated.

       COMPRESS FOR QUERY is useful in data warehousing environments. Valid values are LOW and HIGH, with HIGH providing a higher compression ratio. The default is HIGH.

       COMPRESS FOR ARCHIVE uses higher compression ratios than COMPRESS FOR QUERY, and is useful for compressing data that will be stored for long periods of time. Valid values are LOW and HIGH, with HIGH providing the highest possible compression ratio. The default is LOW.

       Tables with COMPRESS FOR QUERY or COMPRESS FOR ARCHIVE use a PCTFREE value of 0 to maximize compression, unless you explicitly set a value for PCTFREE in the physical_attributes_clause. For these tables, PCTFREE has no effect for blocks loaded using direct-path INSERT. PCTFREE is honored for blocks loaded using conventional INSERT, and for blocks created as a result of DML operations on blocks originally loaded using direct-path INSERT.

 

7. CACHE | NOCACHE | CACHE READS

       Use the CACHE clauses to indicate how Oracle Database should store blocks in the buffer cache. If you specify neither CACHE nor NOCACHE, then:

（1）.      In a CREATE TABLE statement, NOCACHE is the default.

（2）.      In an ALTER TABLE statement, the existing value is not changed.

 

CACHE

        For data that is accessed frequently, this clause indicates that the blocks retrieved for this table are placed at the most recently used end of the least recently used (LRU) list in the buffer cache when a full table scan is performed. This attribute is useful for small lookup tables.

       As a parameter in the LOB_storage_clause, CACHE specifies that the database places LOB data values in the buffer cache for faster access. The database evaluates this parameter in conjunction with the logging_clause. If you omit this clause, then the default value for both BasicFile and SecureFile LOBs is NOCACHE LOGGING.

 

Restriction on CACHE

       You cannot specify CACHE for an index-organized table. However, index-organized tables implicitly provide CACHE behavior.

 

NOCACHE

        For data that is not accessed frequently, this clause indicates that the blocks retrieved for this table are placed at the least recently used end of the LRU list in the buffer cache when a full table scan is performed. NOCACHE is the default for LOB storage.

       As a parameter in the LOB_storage_clause, NOCACHE specifies that the LOB values are not brought into the buffer cache. NOCACHE is the default for LOB storage.

 

Restriction on NOCACHE 

You cannot specify NOCACHE for an index-organized table.

 

CACHE READS 

       CACHE READS applies only to LOB storage. It specifies that LOB values are brought into the buffer cache only during read operations but not during write operations.

 

 

8.  parallel_clause

       The parallel_clause lets you parallelize creation of the table and set the default degree of parallelism for queries and the DML INSERT, UPDATE, DELETE, and MERGE after table creation.

 

Note:

       The syntax of the parallel_clause supersedes syntax appearing in earlier releases of Oracle. Superseded syntax is still supported for backward compatibility but may result in slightly different behavior from that documented.

NOPARALLEL

       Specify NOPARALLEL for serial execution. This is the default.

PARALLEL 

       Specify PARALLEL if you want Oracle to select a degree of parallelism equal to the number of CPUs available on all participating instances times the value of the PARALLEL_THREADS_PER_CPU initialization parameter.

 

       PARALLEL integer Specification of integer indicates the degree of parallelism, which is the number of parallel threads used in the parallel operation. Each parallel thread may use one or two parallel execution servers. Normally Oracle calculates the optimum degree of parallelism, so it is not necessary for you to specify integer.

 

       可通过数据字典表DBA_TABLES、ALL_TABLES、USER_TABLES查看参数设置情况，如：

Select table_name,initial_extent,next_extent,min_extents,max_extents,pct_increase from user_tables;

 

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