Well, not quite. SORT_AREA_SIZE specifies the maximum amount, in bytes, of memory to
use for a sort. After the sort is complete and all that remains to do is to return
the rows, the memory is released down to the size specified by
SORT_AREA_RETAINED_SIZE. After the last row is returned, all memory is freed.
Temporary disk is used for the intermediate sort runs only if the SORT_AREA_SIZE isn't
large enough to handle the sort in memory. The SORT_AREA_RETAINED_SIZE controls the
size of the read buffer which is used to maintain a portion of the sort in memory.
Myself, I use 2048000 for SORT_AREA_SIZE, and 512000 for SORT_AREA_RETAINED_SIZE.
>>> [EMAIL PROTECTED] 04/18/01 11:36AM >>>
I think you are not correct. First - Oracle allocates memory for sorting as
needed by 8K chunks up to sort_area_size. Second if your sort_area_size is
large enough to do sort in memory and your sort_area_retained_size <
sort_area_size oracle will dump sorted data into temporary tablespace and
then read from this tablespace. So it is a tradeoff between late memory
release and temporary tablespace I/O.
Alex Hillman
-----Original Message-----
Sent: Wednesday, April 18, 2001 10:40 AM
To: Multiple recipients of list ORACLE-L
Hi John,
As you mentioned, it depends on a number of factors. I believe I replied to
a question about improving performance of index building after an import.
Anyway, here is the reasoning behind why I said that.... When Oracle begins
sorting, it starts with the memory equal to sort_area_retained_size value
and may eventually acquire memory equal to sort_area_size. This involves at
OS level, malloc (and may be some other) memory mgmt routine(s). After the
sort phase is complete, Oracle will trigger memory de-allocation and the OS
will go at work again. If there are servile sessions performing sorts, there
can be an increased OS level memory mgmt activity (while attaining
sort_area_size and releasing it back to sort_area_retained_size) . But if
the server has *enough* memory keeping sort_area_retained_size equal to
sort_area_size may actually help. I also assume that these days most
installations have ample memory. And that the advice of using 50% (which I
had heard of) of sort area size for sort area retained size should always be
viewed in light of one's requirements and resource availability. But I can't
stop wondering... how come it was 50% and not 10% or 20%.. so it's all
relative. I have been using what I suggested, for a number of years now
with no problems or complaints.
Cheers !
- Kirti Deshpande
Verizon Information Services
http://www.superpages.com
> -----Original Message-----
> From: Hallas, John [SMTP:[EMAIL PROTECTED]]
> Sent: Wednesday, April 18, 2001 6:21 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: Temporary Tablespace Design
>
> FOR YOUR INFORMATION
>
> ESIS and EPFAL are now part of Logica. The Internet email addresses of the
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>
>
> Kirti Deshpande writes
>
> "Also, keep SORT_AREA_RETAINED_SIZE the same as SORT_AREA_SIZE. As the
> former will be used while fetching data after sort phase is completed."
>
> I thought best advice was to make the retained size smaller (50%?) of
> sort_area_size to allow initial sort memory to be released after the first
> part of the sort is managed and only the merge phase of a disk sort is
> left
> to do.
>
> I appreciate that a lot depends on the amount of memory available and the
> number of concurrent processes that may be performing sorts but surely the
> aim is to free memory up as soon as possible down to the
> sort_area_retained_size
>
> Thanks
>
> John
>
> (PS I do apologise for the rubbish at the top of this mail but it is
> inserted after I have sent the mail into our mail gateway)
>
>
>
>
>
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> Author: Hallas, John
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