||Oracle Tips by Burleson
Chapter 6 Oracle Tablespace and File
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.