RE: db_file_multiblock_read_count causing full scans to takelonger?

Understood - I just wanted to make sure you weren't making decisions just based on that small sample.

Interesting - I tested "time dd" on my HPUX 11 system and I see the same behavior you describe - it runs fastest at bs=255k and then takes twice as long as soon as I increase to bs=256k or higher. However on my AIX 5.3 system it seems to max out at about bs=32k and stays pretty consistent all the way to 4096k. Seems like some sort of HPUX limitation. I think the max io size on HPUX is 256k so it makes sense that there would be some difference at that point, but I would expect the difference to occur at 257k, not 256k - and I wouldn't expect it to be such a big difference. You'd think HPUX could split up the larger read requests into 255k chunks a little more efficiently than that. I'll check on a couple more AIX and HPUX systems and see if they exhibit the same behavior too.

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

From: Kevin Lidh [mailto:kevin.lidh_at_gmail.com]

That was just an example from the two trace files. I wanted to show the difference in times retrieving the exact same blocks.

The "time dd" tests are very consistent. Any block size up to 255k performs the same. Once you get to 256k and beyond, the time increases 3x to 4x.

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http://www.freelists.org/webpage/oracle-l Received on Tue Dec 19 2006 - 17:42:56 CST