Queries with high version counts can cause library cache latch contention, as the query must hold that latch during soft parse and has to go through the entire list of query versions in the data dictionary. High version_count's are often caused by a high number of invalidations on the query. Invalidations of a query can be caused by a number of different things (one is the bug with timed_statistics, another is a bug present up to 8.1.6.3 in some instances when materialized views are used), other causes of invalidations are analyzing a dependent table or index, or truncating a dependent table.
If this is causing you a problem, the next step is to track down what the cause of your high version_counts is, and work to correct it or workaround it (depending on the frequency that the query is executed, a shared pool flush may remove all versions (or none)). If it's not causing you a service problem currently, I would still keep an eye on it, as the version_count for queries rises, the chances of getting severe contention on the library cache latch increases.
George
// George Schlossnagle
// www.pythian.com -- [EMAIL PROTECTED] -- 877-PYTHIAN
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On Wednesday, January 2, 2002, at 04:35 PM, [EMAIL PROTECTED] wrote:
Yes, there are a handful with more than 400.
I'm not sure what high is?
Cherie
"George
Schlossnagle" To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]>
<schlossnagle@py cc:
thian.com> Subject: Re: Shared pool wait for library cache pin
Sent by:
[EMAIL PROTECTED]
01/02/02 02:41
PM
Please respond
to ORACLE-L
Do any of your queries have a high version_count (visible through
v$sqlarea)?
George
----- Original Message -----
To: "Multiple recipients of list ORACLE-L" <[EMAIL PROTECTED]>
Sent: Wednesday, January 02, 2002 3:20 PM
We are seeing a lot of shared pool waits (for libary cache pin) on
our 8.1.5 web-based application. We are seeing this via Precise/Indepth
SQL monitoring tool.
I haven't been able to find much documentation on shared pool waits or
library cache pins.
Can anyone tell me what might be causing this problem?
Thanks,
Cherie
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