Compare ALTER TABLE t move and ALTER TABLE T shrink space in Oracle

Source: Internet
Author: User

ALTER TABLE t move and ALTER TABLE t shrink space can be used for segment shrinkage, reducing high water HWM,
can also be used to eliminate row Chaining and row migration (row migration),
But there are the following differences:
1) using ALTER TABLE move, the table is shrunk to the initial size specified by the storage clause when the table was created, and the ALTER table shrink space is not subject to this restriction.
2) After using the ALTER TABLE move, the index will be invalid and need to be rebuilt, using ALTER TABLE shrink space without invalidating the index.
3) ALTER TABLE shrink space can only be used when the table space in which the table resides is automatic segment space management (segment Space MANAGEMENT AUTO clause is specified when creating tablespace).
4) You can use the ALTER TABLE shrink Space compact to defragment the table without adjusting the HWM, and then call ALTER TABLE shrink space again to free up space.
5) You can use ALTER TABLE shrink space cascade to simultaneously contract the index, which is equivalent to executing the ALTER index shrink space at the same time.

Compare ALTER TABLE t move and ALTER TABLE T shrink space in Oracle

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