Every Tablespace has default storage parameters. To override the system defaults in that Tablespace, a user can specify the parameters while creating the objects. The following are the parameters:
INITIAL: The size in bytes of the first extent allocated when a segment is created. Though default system values are given data blocks, use bytes to set a value for this Parameter. You can also use the abbreviations K and M to indicate Kilobytes and Megabytes.
Default:5 datablocks
Minimum:2 datablocks
Maximum:Operating system specific
NEXT: The size of the next extent to be allocated for a segment. The second extent is equal to the original setting for next. From third extent onwards ‘Next’ is set to the previous size of Next multiplied by (1+Pctincrease/100). You can also use K and M for kilobytes and megabytes as above.
Default:5 datablocks
Minimum:1 datablock
Maximum:Operating system specific
MAXEXTENTS: The total number of extents, including the first, can ever be allocated for the segment.
Default:Dependent on the data block size and operating system
Minimum:1 (extent)
Maximum:Operating system specific
MINEXTENTS: The total number of extents to be allocated when the segment is created. This allows for a large allocation of space at creation time, even if contiguous space is not available.
Default:1 (extent)
Minimum:1 (extent)
Maximum:Operating system specific
If minextents are more than 1, then the specified number of incremental extents is allocated at creation time using initial, next, pctincrease.
PCTINCREASE: The percent by which each incremental extent grows over the last incremental extent allocated for a segment. If pctincrease is 0, then all incremental extents are the same size. If pctincrease is greater than 0, then each time the next is calculated, it grows by pctincrease. It cannot be negative. It is specified in percentage.
Default:50 (%)
Minimum:0 (%)
Maximum:Operating system specific
Note: Pctincrease for Rollback Segment is always 0. Pctincrease cannot be specified for Rollback Segments.
PCT FREE: It is used to set percentage of a block to be reserved (kept free) for future updates. After this parameter is met the block is considered to be full and it is not available to insert new rows.
PCTUSED: It is used to allow a block to be reconsidered for the insertion of new rows. When the percentage of a block being used falls below PCTUSED either through row deletion or updates reducing column storage, the block is again available for insertion of new rows.
INITTRANS: It reserves pre-allocated amount of space for initial number transaction entries to access rows in the data block concurrently. Space is reserved in the header of all data blocks of all associated data or index segment. The default value is 1 for tables and 2 for clusters.
MAXTRANS: As multiple transactions concurrently access the rows of the same data block, space is allocated for each transaction’s entry in the block
Once the space is reserved by the inittrans is depleted, space for additional transaction entries is allocated out of the free space in a block, if available. Once allocated, this space effectively becomes a permanent part of the block header. The maxtrans parameter is used to limit the no. of transaction entries that can concurrently use data in a data block.
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