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Home -> Community -> Mailing Lists -> Oracle-L -> RE: Excessive library cache latch contention
Harvey,
Personally, I would go right to the user(s) who has complained about the slowdown and have them run the application at the peak hour/period where things seem very slow.
Set a 10046 event level 8 trace on that session(s) after they log on and then take a look at the trace file in the udump area after they are finished executing the queries.
There should be some strong clues in there about why the session is the waiting.
My bet is on some poorly written SQL and these session competing for blocks.
Check out Oracle Performance Tuning 101 Book and you can send your 10046 event data to www.hotsos.com for review if you are confused by it
fwiw. good luck. mike
-----Original Message-----
Sent: Friday, January 31, 2003 3:09 AM
To: Multiple recipients of list ORACLE-L
We've got about 30 sites all running the same application, and I'm consistently seeing large numbers of 106 (library cache) latch free waits. They tend to happen at peak times during the day, and in the worst case I saw 12 sessions all on a 106 latch free wait event, spread across 3 P1RAW addresses.
Running Steve Adams latch_sleeps scripts, yields the following:
LATCH TYPE IMPACT SLEEP RATE WAITS HOLDINGLEVEL
library cache 1281502 0.11% 2399666 5 cache buffers chains 273556 0.00% 23049 1 shared pool 73893 0.04% 91633 7 cache buffers lru chain 12236 0.01% 70756 3 session allocation 10639 0.06% 19969 5 row cache objects 7835 0.00% 29816 4 cache buffer handles 3646 0.00% 2575 3 transaction allocation 2344 0.01% 4341 8 enqueue hash chains 1831 0.01% 13722 4 redo writing 778 0.01% 17328 5 session idle bit 714 0.00% 01
The results above are from an instance which has been up for 5 days
As you can see, library cache latch has a big impact (though I must admit, I'm not sure what Steve's IMPACT formula actually tells me). When I check across other sites, I see a similar pattern - large numbers of 106 latch misses and sleeps.
I guess what I'd like to know is where these latches are happening, which objects / cursors etc are causing the contention. I've grappled with SQL against x$kglob, trying to join back to the P1RAW but am not getting very far.
Any ideas?
TIA. Neil.
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Author: Harvey Neil
INET: Neil.Harvey_at_sx3.com
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