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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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