Re: Excessive child cursors

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

--Terry
  hi

  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?

  thanks

  --
  LSC


  On 9/27/07, Terry Sutton <terrysutton@xxxxxxx> 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 10.2.0.3 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". :-)

    --Terry

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