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$sysstat, during these 3 steps, and did not see the expected results. It
was a rudimentary test on a high volume database, so I guess I could have
been wrong. I remember I tried this coz I read a post from Jonathan Lewis,
suggesting that the initial memory for sorting is allocated in the UGA upto
sort_area_retained_size, after which it is allocated from the PGA upto
sort_area_size.
Thanks
Raj
DENNIS WILLIAMS
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Sent by: Subject: RE: SORT_AREA_SIZE question
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06/25/2003
04:27 PM
Please respond
to ORACLE-L
Raj
From our perspective as users of the operating system we expect when we
release memory that the O.S. will immediately release it to other users.
>From the O.S. perspective, that is treated more like a suggestion. The O.S.
has many tasks to accomplish and reusing released memory is pretty low on
the list of priorities.
Dennis Williams
DBA, 80%OCP, 100% DBA
Lifetouch, Inc.
[EMAIL PROTECTED]
-----Original Message-----
Sent: Wednesday, June 25, 2003 1:31 PM
To: Multiple recipients of list ORACLE-L
Since we are talking of Sort area sizes here, I tried to collect some
statistics on the amount of memory used by each dedicated Oracle
connection. As I understand it, the PGA is allocated in chunks upto the
SORT_AREA_SIZE. Initially, I just started a session, and noted down the
memory used using pmap. Then, I did a small sort, and then, a huge sort,
noting the memory utilization each time. I was even monitoring the PGA
statistics in v$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
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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
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