RE: low blocks/read on temp

From: John Kanagaraj <john.kanagaraj_at_hds.com>
Date: Tue, 26 Jul 2005 15:58:47 -0700
Message-ID: <960A9B249C99994AA3C7FCA016A0DA8902AA0B53@ussccem08.corp.hds.com>

Dave,

Just wondering how you measured the avg blocks per read (I might be too dense and missed something...) In any case, the largest I/O that the OS can service is determined by the 'maxio' parameter (or its equivalent in Tru64). Normally, this is 64K, but I believe this can be tweaked up to 1MB. So, even if you set a unnaturally high DBFMBRC, the OS will limit what it provides back... Steve Adams has a script at his site that measures the actual DBFMBRC, but I belive that goes against non TEMP data...

Hth,
John Kanagaraj <><
DB Soft Inc
Phone: 408-970-7002 (W)

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From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Allen, Brandon
Sent: Tuesday, July 26, 2005 3:33 PM
To: Dave.Herring_at_acxiom.com; Oracle-L_at_Freelists. Org (E-mail) Subject: RE: low blocks/read on temp

Hi Dave,

I just checked a few of my databases and the highest was 7 blocks per read, the lowest was 1.9. Why would you expect it to be so high? I believe the blocks per read for TEMP is a function of your db_file_multiblock_read_count, extent sizes, and cached blocks, just like with any other tablespace. Not sure if this is correct though since I think TEMP is usually read with direct reads (bypassing the buffer cache) and I'm not sure if direct reads determine their blocks/read the same way as regular db_file_sequential/scattered_reads.

Regards,
Brandon

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org]On Behalf Of Herring Dave - dherri
Sent: Tuesday, July 26, 2005 3:09 PM
To: Oracle-L_at_Freelists. Org (E-mail)
Subject: low blocks/read on temp

Has anyone run into situations where the avg blocks per read against their temporary tablespace seemed extremely low? We have a database block size of 32K, yet I'm seeing blocks per read on TEMP 5.2, on average. I would expect much, much higher, at least in the 20's. Is this a realistic expectation?

I'm running 9.2.0.4 on Tru64 5.1.

Thanks.

Dave

Dave Herring, DBA

Acxiom Corporation

3333 Finley

Downers Grove, IL 60515

wk: 630.944.4762

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http://www.freelists.org/webpage/oracle-l Received on Tue Jul 26 2005 - 18:01:00 CDT