这个需要解释的就多了,都是和存储数据有关的参数,
如果不是想做研究的话,就不要管了。
解释其中的几个:
*PCTFREE
The PCTFREE parameter is used to set the percentage of a block to be reserved for possible updates to rows that already are contained in that block. For example, assume that you specify the following parameter within a CREATE TABLE statement: PCTFREE 20 This indicates that 20% of each data block used for this table's data segment will be kept free and available for possible updates to the existing rows already within each block.*PCTUSED
After a data block becomes full as determined by PCTFREE, Oracle does not consider the block for the insertion of new rows until the percentage of the block being used falls below the parameter PCTUSED. Before this value is achieved, Oracle uses the free space of the data block only for updates to rows already contained in the data block. For example, assume that you specify the following parameter within a CREATE TABLE statement: PCTUSED 40
In this case, a data block used for this table's data segment is not considered for the insertion of any new rows until the amount of used space in the block falls to 39% or less (assuming that the block's used space has previously reached PCTFREE).
如果不是想做研究的话,就不要管了。
解释其中的几个:
*PCTFREE
The PCTFREE parameter is used to set the percentage of a block to be reserved for possible updates to rows that already are contained in that block. For example, assume that you specify the following parameter within a CREATE TABLE statement: PCTFREE 20 This indicates that 20% of each data block used for this table's data segment will be kept free and available for possible updates to the existing rows already within each block.*PCTUSED
After a data block becomes full as determined by PCTFREE, Oracle does not consider the block for the insertion of new rows until the percentage of the block being used falls below the parameter PCTUSED. Before this value is achieved, Oracle uses the free space of the data block only for updates to rows already contained in the data block. For example, assume that you specify the following parameter within a CREATE TABLE statement: PCTUSED 40
In this case, a data block used for this table's data segment is not considered for the insertion of any new rows until the amount of used space in the block falls to 39% or less (assuming that the block's used space has previously reached PCTFREE).
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都是storage clause ,oracle 和SQLserver 不一样,你可以自己来定义有关table extend
的storage parameter摘录一些ORACLE的manual吧:
INITIAL specifies in bytes the size of the object's first extent. Oracle allocates space for this extent when you create the schema object. Use K or M to specify this size in kilobytes or megabytes. The default value is the size of 5 data blocks. The minimum value is the size of 2 data blocks for nonbitmapped segments or 3 data blocks for bitmapped segments, plus one data block for each free list group you specify. The maximum value depends on your operating system. Oracle rounds values up to the next multiple of the data block size for values less than 5 data blocks, and rounds up to the next multiple of 5 data blocks for values greater than 5 data blocks. Restriction: You cannot specify INITIAL in an ALTER statement. NEXT specifies in bytes the size of the next extent to be allocated to the object. Use K or M to specify the size in kilobytes or megabytes. The default value is the size of 5 data blocks. The minimum value is the size of 1 data block. The maximum value depends on your operating system. Oracle rounds values up to the next multiple of the data block size for values less than 5 data blocks. For values greater than 5 data blocks, Oracle rounds up to a value that minimizes fragmentation. If you change the value of the NEXT parameter (that is, if you specify it in an ALTER statement), the next allocated extent will have the specified size, regardless of the size of the most recently allocated extent and the value of the PCTINCREASE parameter. MINEXTENTS specifies the total number of extents to allocate when the object is created. This parameter enables you to allocate a large amount of space when you create an object, even if the space available is not contiguous. 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. 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 parameters. Restriction: You cannot specify MINEXTENTS in an ALTER statement. MAXEXTENTS specifies 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 value of 2). The default value depends on your data block size. PCTINCREASE specifies 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 (that is, if you specify it in an ALTER statement), Oracle calculates the size of the next extent using this new value and the size of the most recently allocated extent. Suggestion: If you wish to keep all extents the same size, you can prevent SMON from coalescing extents by setting the value of PCTINCREASE to 0. In general, Oracle Corporation recommends a setting of 0 as a way to minimize fragmentation and avoid the possibility of very large temporary segments during processing. Restriction: You cannot specify PCTINCREASE for rollback segments. Rollback segments always have a PCTINCREASE value of 0.
After a data block becomes full as determined by PCTFREE, Oracle does not consider the block for the insertion of new rows until the percentage of the block being used falls below the parameter PCTUSED. Before this value is achieved, Oracle uses the free space of the data block only for updates to rows already contained in the data block. For example, assume that you specify the following parameter within a CREATE TABLE statement: PCTUSED 40
In this case, a data block used for this table's data segment is not considered for the insertion of any new rows until the amount of used space in the block falls to 39% or less (assuming that the block's used space has previously reached PCTFREE).