SMON coalesce

Printable View

04-10-2002, 02:52 AM
Sonia

hi folks,

Why does SMON coalesces free space only when we set the PCTINCREASE>0.
what is the logic behind this.

Regards
sonia
04-10-2002, 03:13 AM
julian

SMON wakes up every 5th minute and checks for tablespaces with default pctincrease != 0. However, SMON might not coalesce all free space every time it runs.

Coalescing means gathering together small chunks of free space into larger chunks of free space. This hopefully answers your 2nd question.
04-10-2002, 11:38 AM
marist89

Quote:

Originally posted by Sonia
hi folks,

Why does SMON coalesces free space only when we set the PCTINCREASE>0.
what is the logic behind this.

In theory, if PCTINCREASE = 0, you won't need to coalesce because your extents will be equally sized. Therefore, they can be reused without being coalesced into bigger chunks.
04-10-2002, 01:34 PM
Sonia

Thanx Jeff

U have got the point there.

Regards
sonia
04-10-2002, 09:53 PM
thanigai

yes..remember the next extent calculation formula
next extent=next extent(1+pctincrease/100)...
Thanks.
Thanigaivasan
04-10-2002, 11:09 PM
rameshk

when you insert data into extents, DBWR looks for an extent which is bigger than the current extent (if PCTINCREASE > 0). If SMON doesn't coalesce the free space into larger extents, data never gets inserted into those extents and the tablespace gets fragmented.
04-11-2002, 01:49 AM
julian

Quote:

Originally posted by rameshk
when you insert data into extents, DBWR looks for an extent which is bigger than the current extent (if PCTINCREASE > 0). If SMON doesn't coalesce the free space into larger extents, data never gets inserted into those extents and the tablespace gets fragmented.

The space allocation in Oracle is not that simple, it depends on several things: if the request for space would occupy more or less than 5 blocks, if Oracle needs to split the extent or find an exact match and on the order of the listed free extents in the SGA.