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  Oracle Tips by Burleson

Chapter 6 Oracle Tablespace and File Internals Scripts

There is probably nothing to worry about after coalescing, unless the number of extents is 20 or more, and the mismatch between the biggest area and the free area is 10 percent or more. If either of these values is exceeded, the DBA should consider using the defragmentation methods described earlier. This report does not cover temporary tablespaces that are created as CREATE TEMPORARY TABLESPACE using tempfiles. 

Beginning with version 8, the tablespaces are automatically defragmented by the SMON process if the value for the default storage parameter pctincrease is set greater than 0. The free space fragmentation index (FSFI), from the Oracle DBA Handbook, by Kevin Loney (Oracle Press, 1994), shows how much freespace in a tablespace is fragmented. A high value is good (with 100 the best); a low value is bad.

If it becomes necessary to add data files to a single tablespace in a short period of time, it may be wise to extrapolate the growth and then export, drop, and re-create the tablespace to a size large enough to prevent excessive addition of data files. Oracle suggests using autoextend data files for tablespaces that are expected to grow. However, there is something to be said for manual control of tablespace growth. With autoextend, a runaway insert or other database mishap can cause the tablespace to grow unpredictably. Autoextend can work very well in a stable production environment, so long as the DBA has a firm understanding of the way the tablespaces are likely to grow. 

The above text is an excerpt from:

Mike Ault’s Oracle Internals Monitoring & Tuning Scripts

See the Oracle script collection::



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