RE: Aligning Oracle Blocks with Filesystem Block Size

  • From: "Richard J. Goulet" <rgoulet@xxxxxxxxxx>
  • To: <oracle-l@xxxxxxxxxxxxx>
  • Date: Tue, 14 Nov 2006 10:13:34 -0500


    Having been a long time HP-UX and OnlineJFS user, your making the
machine do more work than is needed.  Assume that your looking for one
row of data in one data block.  HP is going to read 2 data blocks of
data into memory for you.  The Oracle manuals are pretty good at saying
that your database block size should be equal to or a multiple of the OS
block size.  BTW: you've also put dbwr into a quagmire at the same time.
Since it's wetting 4K blocks the OS is going to cache those writes till
it gets an 8k write to that disk location before it does anything.  Now
I'm not sure what it does in the event that you never write the
remaining 4K of data, but I'd imagine that it would cache the 4k block
in swap for a rather long time.


Dick Goulet, Senior Oracle DBA

45 Bartlett St  Marlborough, Ma 01752, USA
Tel.: 508.573.1978 |Fax:  508.229.2019 | Cell:508.742.5795 




From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of amonte
Sent: Tuesday, November 14, 2006 9:59 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Aligning Oracle Blocks with Filesystem Block Size


I have a 9i database running on HP-UX which uses 4k db_block_size. The
filesystem used is OnlineJFS (vxfs version 4).

The Filesystem block size is 8k (f_bsize 8192)

I was wondering what sort of impact can this missalignment cause? Would
I/O system perform twice I/O it should? 



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