Re: SORT_AREA_SIZE question

The original question does not appear to have been answered.

The question on 'reporting database/data mart' with lots of FTS does not suggest S_A_S will provide any significant benefits regardless of how you tweak the parameters.

What is more likely to provide benefits is to look at how the DSS type of environment is designed and constructed, especially partitioning, and for 'datamarts', you have already constructed the schemas such that the queries are simple and the only sorting you need to do are to ensure the results are returned in order.

As for pmap showing memory utilisation, it is not that straightforward to interpret - there is a Metalink doc showing how to do that correctly. 'top' gives a pretty good idea once you have worked out what the SGA component of the shared-memory should be.

As for S_A_S, I suspect it will buy you very little. Look at all the other DW types of features you can make use of - like range-partitioning, hash-partitioning, or some combination thereoff.

• Original Message ----- To: Multiple recipients of list ORACLE-L <[EMAIL PROTECTED]> Sent: Thursday, June 26, 2003 10:04 AM

>
> Thanks Dennis. My question was not about the memory release, but more of
> the way memory is allocated to the PGA. Given that Oracle allocates memory
> in small chunks to the PGA until it approaches the sort area size, if I
run
> a huge sort, should I expect the PGA memory to increase, until it reaches
> sort_area_size?
>
> 1. Initial dedicated connection established. The PGA used should be very
> minimal.
>
> 2. Say, I invoke a small sort on DBA_USERS. The PGA (or UGA) should
> increase by a very small value.
>
> 3. I invoke a sort on a huge table. I expect the PGA to keep increasing,
> and flatten out once it reaches the SORT_AREA_SIZE.
>
> I tried to monitor the memory utilization by the session using pmap, and
> v$sysstat, during these 3 steps, and did not see the expected results. It
> was a rudimentary test on a high volume database, so I guess I could have
> been wrong. I remember I tried this coz I read a post from Jonathan Lewis,
> suggesting that the initial memory for sorting is allocated in the UGA
upto
> sort_area_retained_size, after which it is allocated from the PGA upto
> sort_area_size.
>
> Thanks
> Raj
>
>
>
>
>
> DENNIS WILLIAMS
> <[EMAIL PROTECTED] To: Multiple recipients of
list ORACLE-L <[EMAIL PROTECTED]>
> TOUCH.COM> cc:
> Sent by: Subject: RE: SORT_AREA_SIZE
question
> [EMAIL PROTECTED]
> ty.com
>
>
> 06/25/2003
> 04:27 PM
> Please respond
> to ORACLE-L
>
>
>
>
>
>
> Raj
> From our perspective as users of the operating system we expect when we
> release memory that the O.S. will immediately release it to other users.
> From the O.S. perspective, that is treated more like a suggestion. The
O.S.
> has many tasks to accomplish and reusing released memory is pretty low on
> the list of priorities.
>
> Dennis Williams
> DBA, 80%OCP, 100% DBA
> Lifetouch, Inc.
> [EMAIL PROTECTED]
>
>
> -----Original Message-----
> Sent: Wednesday, June 25, 2003 1:31 PM
> To: Multiple recipients of list ORACLE-L
>
>
>
> Since we are talking of Sort area sizes here, I tried to collect some
> statistics on the amount of memory used by each dedicated Oracle
> connection. As I understand it, the PGA is allocated in chunks upto the
> SORT_AREA_SIZE. Initially, I just started a session, and noted down the
> memory used using pmap. Then, I did a small sort, and then, a huge sort,
> noting the memory utilization each time. I was even monitoring the PGA
> statistics in v$sysstat. I was expecting the sizes to increase, and then
> decrease when the sorting was done with. (retained_size was 0). I dont
> recall my observations rite now, but it was definitely not what I
expected.
>
> Has anyone done something similar? Are my expectations rite?
>
> Thanks
> Raj
>
>
>
>
> DENNIS WILLIAMS
>
> <[EMAIL PROTECTED] To: Multiple recipients of
> list ORACLE-L <[EMAIL PROTECTED]>
> TOUCH.COM> cc:
>
> Sent by: Subject: RE: SORT_AREA_SIZE
> question
> [EMAIL PROTECTED]
>
> ty.com
>
>
>
>
>
> 06/25/2003
>
> 12:30 PM
>
> Please respond
>
> to ORACLE-L
>
>
>
>
>
>
>
>
>
> Bart -
> No it hasn't been recently asked.
> 1. SORT_AREA_SIZE is per-process. So be a little wary. Keep in mind
> that
> in-memory sorts are much faster than disk sorts. But you knew that.
> 2. Ask your system administrator to monitor whether your system is
> getting paging/swapping.
> 3. Find out how many disk sorts are occurring. I prefer STATSPACK. Try
> to get a handle on how may disk vs. memory sorts are occurring. Try to
> increase SORT_AREA_SIZE until you have few disk sorts, but not so large
you
> cause paging/swapping. Also look at your temp space settings to make sure
> when disk is used, it is used most efficiently. With a data mart, you may
> have some really large sorts that will always be too large for memory
> sorts.
>
>
>
> Dennis Williams
> DBA, 80%OCP, 100% DBA
> Lifetouch, Inc.
> [EMAIL PROTECTED]
>
> -----Original Message-----
> Sent: Wednesday, June 25, 2003 9:39 AM
> To: Multiple recipients of list ORACLE-L
>
>
> Hello,
>
> I joined this list last week, so I apologize in advance if I'm asking a
> question that has previously been answered.
>
> I am responsible for a reporting database/data mart that is approximately
> 175 GB. Our main fact table ranges from 1-14 GB depending upon how far
> along we are into our financial year. I have large reports that run full
> table scans on this table daily. In an effort to keep as much of the
> sorting in memory as possible I have specified SORT_AREA_SIZE to be 100MB.
> Some of the tuning books I am reading now are making me second-guess
myself
> and I am wondering if this is overkill.
>
> Can anyone provide some advice on how large they are setting their
> SORT_AREA_SIZE values for their DSS systems?
>
> Thanks in advance,
>
> Bart
>
>
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.net
> --
> Author:
> INET: [EMAIL PROTECTED]
>
> Fat City Network Services -- 858-538-5051 http://www.fatcity.com
> San Diego, California -- Mailing list and web hosting services
> ---------------------------------------------------------------------
> To REMOVE yourself from this mailing list, send an E-Mail message
> to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
> the message BODY, include a line containing: UNSUB ORACLE-L
> (or the name of mailing list you want to be removed from). You may
> also send the HELP command for other information (like subscribing).

-- 
Please see the official ORACLE-L FAQ: http://www.orafaq.net
-- 
Author: Binley Lim
  INET: [EMAIL PROTECTED]

Fat City Network Services    -- 858-538-5051 http://www.fatcity.com
San Diego, California        -- Mailing list and web hosting services
---------------------------------------------------------------------
To REMOVE yourself from this mailing list, send an E-Mail message
to: [EMAIL PROTECTED] (note EXACT spelling of 'ListGuru') and in
the message BODY, include a line containing: UNSUB ORACLE-L
(or the name of mailing list you want to be removed from).  You may
also send the HELP command for other information (like subscribing).