RE: Partitionining perfortmance degraded drastically after upgrading the database from Oracle 102.0.4 to Oracle 11.2.0.3

Date: Fri, 9 Jan 2015 12:19:59 -0500
Subject: Re: Partitionining perfortmance degraded drastically after upgrading the database from Oracle 102.0.4 to Oracle 11.2.0.3 From: mark.brinsmead_at_gmail.com
To: ashoke.k.mandal_at_medtronic.com
CC: oracle-l-bounce_at_freelists.org; oracle-l_at_freelists.org

It rather looks like you have cut your SGA from 6 GB (which may already have been rather lean) to 1GB, and reduced the total available memory from 12 GB to 6GB.

Why are you surprised that this affects performance? I doubt the problem you are encountering has anything to do with Partitioning. There is probably almost NO memory available for buffer cache, and quite likely too little for the shared pool, too. The (more modest) reduction in memory available for the PGA may affect execution plans by causing a bias from HASH joins toward NESTED LOOPS.

Commonly, people choose (need) to increase the memory available to the SGA when upgrading. At the very least, they will keep memory unchanged. Slashing the memory footprint in half is an uncommon move during an upgrade, and one that you will probably want to rethink.

If you want more help here, let's start with some DATA. Something like the "Top-5 Waits" for pre- and post-upgrade might be a good place to start. After that, perhaps execution plans and wait information for the (most) affected queries. Without this, people here can only guess at the actual cause of your problem, although if enough of us guess for a long enough time, somebody will undoubtedly find the right answer eventually. (My money is on the changes to memory; I suggest we eliminate THAT as a cause before we move on to other possibilities, since we KNOW that was changed.)

On Fri, Jan 9, 2015 at 8:58 AM, Mandal, Ashoke <ashoke.k.mandal_at_medtronic.com> wrote: Greetings All,

I have upgraded one of my 2TB databases with partitioned tables & indexes from Oracle 10.2.0.4 to Oracle 11.2.0.3 recently and experiencing severe poor query performance. The response time of the queries have increased by 20-25 times.

Before the upgrade to 11g

PGA_AGGREGATE_TARGET=6GB

SGA_TARGET=4GB

SGA_MAX_SIZE=6GB

After the upgrade to 11g
MEMORY_TARGET=6GB

PGA_AGGREGATE_TARGET=0

SGA_TARGET=0

SGA_MAX_SIZE=1GB

My understanding is that if I set SGA_TARGET and PGA_AGGREGATE_TARGET parameters to 0 then Oracle manages theses as per the MEMORY_TARGET parameter in 11g. Q. Is it true that the SGA can't grow more than 1GB since SGA_MAX_SIZE is still set to 1GB?

Q2. Will the performance improve by setting  SGA_TARGET to 4GB by default?

Q3. Should I also set the PGA_AGGREGATE_TARGET to GB as it was prior the upgrade?

Q4. Any known issue of partitioning performance impact after you upgrade a 10g database to 11g?

Please let me know if you any suggestions to resolve this issue

Appreciate your help in advance,
Ashoke

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