Re: Performance issue after creating higher block size tablespace - a further question

From: Saad Khan <saad4u_at_gmail.com>
Date: Mon, 1 Mar 2010 10:30:23 -0500
Message-ID: <76b3d4e31003010730t50a30bf7g68439d2c9d3459cf_at_mail.gmail.com>



Hi,

No the problem didnt resolve but since I needed to do something very urgently, I reverted the 8k thing after reading all that which Tom Kyte has written and some of you suggested as well. So now its back to 4k.

But that has done some reorg but I dont think that will resolve the original performance issue. The "do something" song is still being drummed on my head.

On Fri, Feb 26, 2010 at 1:16 PM, girlgeek <girlgeek_at_live.com> wrote:

> I believe that Saad's problem got solved yesterday, but it gave me further
> thought.
>
> Saad said that the application is processing 1 row at a time. Oracle
> operates in blocks. Is it possible that some of his increase in time when he
> increased the block size from 4K to 8K could be simply in the time needed to
> read/write the larger number of bytes for each row processed? Of course, I
> am assuming that each single row will require that a new block be
> read/written. I am ignoring the fact that some of the blocks will already be
> in cache. Guru's what are your answers to this further question.
>
> Thanks,
> Claudia
>
> Oliver Jost wrote:
>
>> Just some two-bits on this one. If you are doing massive inserts are you
>> spending a lot of time allocating space? If so, your rowcache may be very
>> busy allocating more space. You could pre-allocate some space to the segment
>> and increase the size of the next to accommodate future growth.
>> Good luck,
>> Oliver
>>
>> ------------------------------------------------------------------------
>> *From:* oracle-l-bounce_at_freelists.org on behalf of Saad Khan
>> *Sent:* Thu 2/25/2010 12:39 PM
>> *To:* Mark W. Farnham
>> *Cc:* oracle-l_at_freelists.org
>> *Subject:* Re: Performance issue after creating higher block size
>> tablespace
>>
>> No the query plan didnt change, the cost changed very marginally.
>>
>> Yes, i rebuild the indexes after moving the tables.
>>
>> This is 10g, so it gathers stats on base of skewness. The last_analyzed
>> column for this tables shows yesterday.
>>
>> Its the joins that are killing the query i think. I'm going to send the
>> queries to list .
>>
>> DB_CACHE_SIZE was set to 0 as the sga_target is set here which is 1.7 GB
>> (its a 32-bit installation)
>>
>> I couldnt understand your last message. May be if you elaborate it more.
>>
>> Thanks
>>
>>
>> On Thu, Feb 25, 2010 at 12:10 PM, Mark W. Farnham <mwf_at_rsiz.com <mailto:
>> mwf_at_rsiz.com>> wrote:
>>
>> Did your query plan change?
>>
>> Did you also rebuild the indexes after you moved the tables?
>>
>> Gather statistics? Are they a big change from the last time you
>> gathered statistics?
>>
>> Is the new tablespace in files that occupy comparable underlying
>> volumes in terms of I/Os supported per unit time?
>>
>> Is your storage in some flavor of SAME, or were the tables being
>> selected from formerly on independently operating units of i/o
>> (especially from the insert target) and now youíve lumped them all
>> together?
>>
>> What was your db_cache_size before?
>>
>> Are you memory lean on the machine and using filesystems? Have you
>> robbed the OS of file caching space by adding to the SGA size?
>>
>> This is a very critical app and I dont want to rebuild "whole"
>> thing. Moving a bunch of tables is entirely different ofcourse.
>>
>>
>>
>>
>> Those are all bits of a partial change analysis you might do, not
>> that youíve stepped in it. If one or more of them is on target
>> (measure, donít guess) then you might have a shortcut out of your
>> problem. Others might add to the list.
>>
>> Now if you had a time machine, Iíd say get in it and measure
>> things to evaluate what (if any) performance benefit there was to
>> be expected if you could get i/o service time to zero by moving to
>> 8K. Then, if that idealized ceiling of possible benefit was
>> significant, figure what the likely benefit was if everything
>> meshed in your favor with no side effects. Then, if that still
>> seemed worthwhile, plan and engineer the move so that you ruled
>> out in advance negative side effects. (And Iím wondering why not
>> rebuild the whole thing at 8K if the database block size was
>> measured to predict an advantage.)
>>
>> So what to really do now? See where the time is going. One often
>> useful bit of information is routing the output of the select to
>> dev/null and seeing how long that takes. If the lionís share of
>> your time is in the select, fix that. Likewise, if you queue up
>> the results of the select in a single table and just select from
>> there and insert into the destination, does that reveal a
>> bottleneck on the insert side?
>>
>> Before you would move back, you would want to have some evidence
>> that moving back would eliminate some problem. Unless of course
>> the urgency now is such that just getting back where you were
>> right away is more important than minimizing the amount of work to
>> reach better performance. Then you could pretend you went through
>> the time machine, figure out where your time is going and attack
>> the problem from that standpoint.
>>
>> Regards,
>>
>> mwf
>>
>>
>> ------------------------------------------------------------------------
>>
>> *From:* oracle-l-bounce_at_freelists.org
>> <mailto:oracle-l-bounce_at_freelists.org>
>> [mailto:oracle-l-bounce_at_freelists.org
>> <mailto:oracle-l-bounce_at_freelists.org>] *On Behalf Of *Saad Khan
>> *Sent:* Thursday, February 25, 2010 11:24 AM
>>
>> *To:* oracle-l_at_freelists.org <mailto:oracle-l_at_freelists.org>
>> *Subject:* Performance issue after creating higher block size
>> tablespace
>>
>> Hi gurus.
>>
>>
>> I've a production database running on oracle10.2.0.3 at SUSE linux
>> 10. The default DB_BLOCK_SIZE for the database is 4K.
>>
>> There was a performance complain coming from the users and
>> developers asked me to look into that. They particularly
>> complained about one stored procedure that was taking too much
>> time. Now when I looked into the stored proc, I saw the insert
>> statement in one particular table which is something more than 4
>> million rows while selecting from a bunch of other tables.
>>
>> So what I did, I created a new tablespace with the db_block_size
>> 8K and moved all the tables that were used in that SP in the new tbs.
>>
>> And guess what, the new response came after that showed its taking
>> almost double the time as it was taking earlier. The AWR report
>> shows a lot of user IO activity and the tablespace that is hit
>> most is the new one. Now is it due to the different block size for
>> this new tablespace? Is Oracle finding it hard to manage 8k blocks
>> inside the SGA designed for 4K originally?
>>
>> The db_cache_size is set to 8192 and db_8k_cache_size is also set
>> to 8192.
>>
>> Is there any other step I can take? I dont want to revert it back
>> to 4k , I think it should work.
>>
>> Any suggestions?
>>
>> Thanks in advance.
>>
>>
>>
>

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Received on Mon Mar 01 2010 - 09:30:23 CST

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