RE: explain plan, can you explain this?

From: Allen, Brandon <>
Date: Thu, 10 Jan 2008 09:18:47 -0700
Message-ID: <04DDF147ED3A0D42B48A48A18D574C4509EBEDEA@NT15.oneneck.corp>

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.


-----Original Message-----
[] On Behalf Of Yasin Baskan

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

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Received on Thu Jan 10 2008 - 10:18:47 CST

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