Library Cache Lock

8.1.7.4
Windows 2000 Server
ca.200 sessions, about 30 active.

About a dozen sessions go into waits
for Library Cache Lock for the best
part of 300 seconds.  (At which they 
probably all get ORA-04021 and free
themselves, but I couldn't tell, the problem
happened a few minutes before I was due to
leave the site, and the end-users were 
on the other side of the Atlantic). The
odd session might get a library cache pin
wait.

The object they were waiting for (tracked
via x$kglob.kglhdadr = v$session_wait.p1raw)
was a table.  No-one has done ANYTHING
untoward to the table, such as truncate, add column,
index, analyze, for at least 3 days.  The table is
a normal heap table with half a dozen indexes.

The best bet I could come up with was a
metalink item that mentioned conflicts relating
to materialized views - and there is a materialized
view log on this table.

The only other relevant detail I could come up
with is that sessions create a session, work hard
for a few seconds, then drop the session (maintaining
the connection) so the system may be exercising some
part of the code that creates x$kgllk items rather more
heavily than is normal.

Any thoughts ?  Any similar experiences ?


Regards

Jonathan Lewis
http://www.jlcomp.demon.co.uk

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  who can answer the questions, but the 
  person who can question the answers -- T. Schick Jr


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