Hi Gaja , Many thanks for the hints. Yes, we have experienced severe system slowness during this period. I have checked DBA hist active session history and I can see that for the problem time window 'Concurrency' wait ever came all of a sudden. This is happening only in one instance. Top foreground timed events being 'Cursor pin wait on X' and 'Library Cache Mutex-X' waits. A severity 1 SR is raised with Oracle for this. There are bugs related to this 'mutex' , SQL high version count , which in fortunately I not available for our platform (Solaris x86 11.2.0.2) Other recommendations were to increase sag , increase interval between memory resize operations ( yes we use AMM) , gathering dictionary and fixed object statistics. The performance was really bad so that we see the Library Hit % being 1.7,0.8,-0.87 etc. I have analysed past trend which shows the % coming down. The ADDM for problem window recommends some session holding a mutex lock and some others waiting for it which contributes 30% of the activity. The SQLs reported were not so bad a these were critical ones which normally works not so bad. The activities that I see in this time on database are the statistics collection jobs , which were running. Not sure whether this has contributed a pressure in Library cache. After we increased sga it's getting to normal state. But due to a (possible) bug I feel this will come again. Regards, Sreejith -- Sent from my iPhone On 05-Apr-2012, at 2:26 AM, Gaja Krishna Vaidyanatha <gajav@xxxxxxxxx> wrote: > Hi Sreejith, > Although I can't help you directly on the SQL you requested, but once you do > start trend this phenomenon, here are a few things that will provide food for > investigation and thought: > > 1) What the are Top 5 Wait Events when this Instance Efficiency Percentage is > low?� > 2) Which SQL statements are being negatively affected by the Top 5 Wait > Events? By how much?� > 3) Is there a problem on your database for the period of the snapshot(s)?� > 4) How does this snapshot's workload compare to a baseline snapshot? > 5) Is there evidence of some sort of abnormal application workload?� > 6) Did you have more parsing than normal?� > > 7) What caused the increased parsing (if applicable)?� > 8) Or was the increased parsing due to automatic memory management stealing > from the shared pool to feed the db buffer cache in response to an increase > I/O load? > > � > > Cheers, > > Gaja > > Gaja Krishna Vaidyanatha, > CEO & Founder, DBPerfMan LLC > http://www.dbperfman.com > http://www.dbcloudman.com > > Phone -�+1-650-743-6060 > http://www.linkedin.com/in/gajakrishnavaidyanathaCo-author:Oracle > Insights:Tales of the Oak Table > -�http://www.apress.com/book/bookDisplay.html?bID14 > Co-author:Oracle Performance Tuning 101 > -�http://www.amazon.com/gp/reader/0072131454/ref=sib_dp_pt/102-6130796-4625766 > Enabling Cloud Deployment & Management for Oracle Databases > > > ________________________________ > From: Sreejith S Nair <Sreejith.Sreekantan@xxxxxxxxxx> > To: oracle-l@xxxxxxxxxxxxx > Sent: Wednesday, April 4, 2012 2:39 AM > Subject: Instance Efficiency Percentages - Library Hit %: in AWR > > Hi Friends, > In AWR under Instance Efficiency Percentages we see a Library Hit % and we > find it very low for one snapshot. I would like to know the trend for few > more days available in AWR snapshots > (dba_hist_snapshot,DBA_HIST_LIBRARYCACHE) using SQL Query. > > Can some one please help with how this % is being calculated. What SQL can > I use to calculate this ? May be for a range of snapshot. Thanks in > Advance. > > 11.2.0.2.0 on Solairs 10 . > > With Regards, > Sreejith > > -- > Sreejith S Nair > Associate Systems Architect | AOS DBA Team > IBS Software Services Private Ltd. > 2nd Floor, IBS Campus, Technopark Campus, Trivandrum - 695 581, Kerala, > India > ((Direct) +91 471 661 4707 ) +91 808 648 5523 > *sreejith.sreekantan@xxxxxxxxxx > 8 www.ibsplc.com > > > > > > DISCLAIMER: > > "The information in this e-mail and any attachment is intended only for > the person to whom it is addressed and may contain confidential and/or > privileged material. If you have received this e-mail in error, kindly > contact the sender and destroy all copies of the original communication. > IBS makes no warranty, express or implied, nor guarantees the accuracy, > adequacy or completeness of the information contained in this email or any > attachment and is not liable for any errors, defects, omissions, viruses > or for resultant loss or damage, if any, direct or indirect." > > > > > > > -- > //www.freelists.org/webpage/oracle-l > > -- > //www.freelists.org/webpage/oracle-l > > -- //www.freelists.org/webpage/oracle-l