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Re: Excessive child cursors

From: Terry Sutton <>
Date: Thu, 27 Sep 2007 08:52:38 -0700
Message-ID: <07e801c8011e$c1d24a10$6b00a8c0@TerrySutton>

Yes, that's my problem. We still have too many child cursors after switching to force.



  if you have histograms for those columns in your predicates then for each cursor you would have X cursor per different column value, this is with SIMILAR

  with FORCE you still have 40-60 child cursors?


  LSC   On 9/27/07, Terry Sutton <> wrote:     I'm trying to resolve a client situation which involves a lot of hard parsing and library cache latch waits, and I'm hoping to bounce some ideas off people.

    The database is on Solaris. cursor_sharing was set to 'SIMILAR'. No, they don't use bind variables, and that's not going to change soon.

    I've found that we have a lot (40-60) of child cursors for some SQL statements. When I look at v$sql_shared_cursor I find that most of the child cursors have Y for bind_mismatch. But when I look at v$sql_bind_metadata the DATATYPE and MAX_LENGTH are identical for all the cursors. So I'm concluding that the bind mismatches are due to the cursor_sharing='SIMILAR' parameter causing new child cursors due to different values for the literals which are being converted to bind variables (please correct me if my conclusion is unwarranted).

    So I'm trying to figure how to solve this issue (short of having the client use bind variables properly). It seems that cursor_sharing='FORCE' would eliminate the bind mismatch problem, since the values of the literals would all convert to the same bind variables. We've changed the cursor_sharing setting, but we're still having library cache latch waits. I'm wondering if the problem is that we still have the child cursors in the shared pool, and each soft parse has to go through the list of child cursors for a given parent to find a matching one. Would flushing the shared pool solve this part of the problem? Or am I missing something else obvious? I'm a bit wary of flushing the shared pool on a DB that is already having contention problems, unless I'm very confident of having it resolve the issue.

    Any input is welcome, even if it's "hey idiot, you missed this". :-)


-- Received on Thu Sep 27 2007 - 10:52:38 CDT

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