RE: Keep buffer cache question

Yes, index and table blocks. No DDL for quite a while and no large DML that I’ve been able to uncover.

No memory pool resizing since January 9, 2019.

Jay Miller
Sr. Oracle DBA
201.369.8355

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Sayan Malakshinov Sent: Thursday, March 14, 2019 6:06 PM
To: dmarc-noreply_at_freelists.org
Cc: ORACLE-L
Subject: Re: Keep buffer cache question

Hi Jay,

Have you checked what is it reading? Index blocks, table blocks or undo? Were there any DDL or huge DML operations? Have you checked v$bh? What about memory settings? AMM/ASMM/manual? Have you checked v$sga_resize_ops?

On Fri, Mar 15, 2019 at 12:22 AM Redacted sender Jay.Miller for DMARC <dmarc-noreply_at_freelists.org<mailto:dmarc-noreply_at_freelists.org>> wrote: Odd issue here. One of our apps reported slightly increased latency on a heavily used database which started Monday evening and has been consistent since. This is not large from a database perspective but the increase of average response time from 1 to 3 microseconds has had a noticeable impact on their performance.

No execution plan changes, a slightly heavier load at peak times (up about 10% from last week) but nothing that I would expect to have such an impact. We still see the increased latency when the server is 90% idle and the load average is 5 (32 cpus, 16 cores).

In doing an AWR report comparison for comparable times one major difference I saw was that 2 frequently run queries were suddenly doing a lot of physical i/o. For a comparable 2 hour period they went from 1.5 million to 1.8 million executions but physical reads increased from 0 to 1.2 million. I sampled a few other random times and this was consistent. The queries are both doing index access. One is an index range scan and the other a unique scan against the primary key.

I checked with the app group and they have no explanation for why the app might suddenly be querying blocks that aren't in cache whereas they weren't last week.

TIA! Jay Miller
Sr. Oracle DBA

--

Best regards,
Sayan Malakshinov
Oracle performance tuning engineer
Oracle ACE Associate
http://orasql.org<https://urldefense.proofpoint.com/v2/url?u=http-3A__orasql.org&d=DwMFaQ&c=nulvIAQnC0yOOjC0e0NVa8TOcyq9jNhjZ156R-JJU10&r=aiKV3Uv2Wo7GqYQcis9TSvB1MZslPOnintrOY1rjG58&m=y-UF_JpJGTABLm5TmUHndm9ytZLICmx2FNZGBXJNiWY&s=rGHmLD6iEx3nrKyoWoywLbo35y00PQ7_jfalmKciyNE&e=>
--

http://www.freelists.org/webpage/oracle-l Received on Fri Mar 15 2019 - 16:01:49 CET