RE: explain plan, can you explain this?

  • From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
  • To: <yasin.baskan@xxxxxxxxxxxxxxxx>, <john.kanagaraj@xxxxxxxxx>, <dannorris@xxxxxxxxxxxxx>, "Oracle L" <oracle-l@xxxxxxxxxxxxx>
  • Date: Thu, 10 Jan 2008 09:18:47 -0700

SQL Stats are definitely reported as a delta in statspack reports.  I
think maybe the confusion is due the fact that the values reported by
spreport can be invalid for at least a couple different reasons:

1) The stat may only be reported at the _completion_ of the query, so
for example, if a query is running for 10 hours, that processing won't
be reported during any of the snapshots while the query was actually
running, and then, if you look at a 15 minute snapshot from before and
after the completion of the query, it will show 10 hours worth of
elapsed time for that query in a 15 minute window.  I think this effect
differs from version to version, depending on how frequently the stats
in v$sql are updated for a running query.

2) If a query is aged out of the pool, the stats from v$sql are reset,
so this can throw off the delta calculations and even make it negative,
e.g. at snapshot #100, query A has 1,000,000 buffer_gets, but at
snapshot #110, query A has been aged out of the pool and reloaded and
now shows only 1,000 buffer_gets, so when you run spreport from snapshot
100 to 110, you'll get 1,000-1,000,000=(-999,000) for this query.

Regards,
Brandon

-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Yasin Baskan


John, are you sure that statspack reports sql statistics cumulatively?

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