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What does coalescing a tablespace do?
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Answer / guest
A free extent in a dictionary-managed tablespace is made up
of a collection of contiguous free blocks.
When allocating new extents to a tablespace segment, the
database uses the free extent closest in size to the
required extent. In some cases, when segments are dropped,
their extents are deallocated and marked as free, but
adjacent free extents are not immediately recombined into
larger free extents. The result is fragmentation that makes
allocation of larger extents more difficult.
Oracle Database addresses fragmentation in several ways:
When attempting to allocate a new extent for a segment, the
database first tries to find a free extent large enough for
the new extent. Whenever the database cannot find a free
extent that is large enough for the new extent, it
coalesces adjacent free extents in the tablespace and looks
again.
The SMON background process periodically coalesces
neighboring free extents when the PCTINCREASE value for a
tablespace is not zero.
If you set PCTINCREASE=0, no coalescing of free extents
occurs. If you are concerned about the overhead of ongoing
coalesce operations of SMON, an alternative is to set
PCTINCREASE=0, and periodically coalesce free space
manually.
Manually Coalesce any adjacent free extens user this
command:
ALTER TABLESPACE <<TABLESPACENAME>> COALESCE
| Is This Answer Correct ? | 18 Yes | 1 No |
Answer / prashe
Coalescing is only valid for dictionary-managed tablespaces
and de-fragments space by combining neighboring free extents
into large single extents.
| Is This Answer Correct ? | 5 Yes | 5 No |
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