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Shrink space cascade tips

Oracle Tips by Burleson

Oracle 10g Pro-Active Space Management

In Oracle 10g, the tablespace disk space utilization is proactively managed by the database. The Server Alert Mechanism monitors Tablespace disk space utilization.

Information gathered into the AWR is also used to do the growth trend analysis and capacity planning of the database. The background process (MMON) verifies tablespace thresholds. The threshold is reached if the allocated space in the tablespace has reached a certain percentage of the total size of the tablespace (if the threshold is configured as a percentage), or when the total allocated space has reached a certain value that is set by you. An alert is triggered when the threshold has been reached.

Shrink space cascade tips

Another important and useful feature introduced in 10g is the facility to shrink the segment. In the previous releases of the Oracle database, moving or redefining the segment was the only way to free space once allocated below the segment’s HWM.

In Oracle 10g, you can now shrink segments. When a segment is shrunk, its data is compacted, its HWM is pushed down, and unused space is released back to the tablespace containing the segment. This is possible for the segments in Automatic Segment Space Managed (ASSM) tablespaces only. For example, to shrink the table sales_items, use the statement:

ALTER TABLE sales_items SHRINK SPACE CASCADE;

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