Applies to:Oracle Server - Enterprise Edition - Version: 188.8.131.52
Information in this document applies to any platform.
The default value for the parameter is TRUE. This hidden parameter supersedes parameter cell_partition_large_extents which was introduced in 184.108.40.206.
Similarly parameter _index_partition_large_extents was introduced for partitioned indexes, the default value for this one is FALSE.
Smaller size extents impacts performance of operations like load and scan, typically full table scan FTS (multi-block IO). For partitioned objects with many partitions, the fact of having many partitions leads to more small extents with autoallocation than for a nonpartitioned table; more smaller extents lead to more expensive space allocation/deallocation operations, and the I/O performance of scanning can be impacted due to more extents with smaller extent size.
The change of the default allocation size for partitioned tables was introduced together with the enhanced deferred segment creation support for partitioned tables in 220.127.116.11 (deferred_segment_creation parameter, default TRUE).
Using both new defaults ensures that a negative impact from pre-created partitioned tables could be ruled out since empty partitions will no longer allocate any space.
If the user forcefully sets the parameter _partition_large_extents to FALSE (either at session or at instance level), then the pre-18.104.22.168 behaviour (of starting from 64k extent size) will be restored.
The user can also override the default extent allocation on a per statement base by specifying INITIAL extent in the CREATE TABLE ... / ALTER TABLE ... ADD PARTITION ... command as well as by changing the default storage initial for the tablespace involved e.g. ALTER TABLESPACE ... DEFAULT STORAGE (INITIAL 65536);