RE: Temporary Tablespace Design

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:HallasJ_at_logicae.com]
> Sent: Wednesday, April 18, 2001 6:21 AM
> To: Multiple recipients of list ORACLE-L
> Subject: RE: Temporary Tablespace Design
>
> FOR YOUR INFORMATION
>
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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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>
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> Author: Hallas, John
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Author: Deshpande, Kirti
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