RE: Db_block

From: Veronica Levin <vlevin_at_victoria.com.ni>
Date: Wed, 14 Jun 2000 11:55:27 -0600
Message-Id: <10528.109273@fatcity.com>

Hi Alex,
Is there a site where I can read that document? Thanks in advance!
=20
Saludos,=20

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-----Mensaje original-----
De: Alex Hillman [mailto:alex_hillman_at_physia.com] Enviado el: Viernes 9 de Junio de 2000 4:49 PM Para: Multiple recipients of list ORACLE-L Asunto: RE: Db_block_size

Maybe this rule of thumb a little outdated. First it depends on what = kind
of file system you run (journal or not), if your box can use direct IO, = what
is the block size of your file system, what is the maximum I/O size of = your
box, can you change it (before Solarid 2.7 max size was 64K, 2.7 and up = you
can configure it in /etc/system). Generally, if direct I/O is enabled, = your
block size should be equal file system block size. Standard file system block size is 8K but you can create file system with bigger block size = like
16k and make your Oracle block size 16K. There is an article on Steve = Adams
site why large block size is better - for OLTP mainly because of = lowering of
the haight of the indexes . So it is a little more complex that it = looks
like. There were very good presentations on IOUG by Gaja = Vaidyanatha(sucking
up :-) ) about performance tuning and RAIDs where these issues were explained.

Alex Hillman=20

-----Original Message-----=20
From: guy ruth hammond [ mailto:grh_at_agency.com <mailto:grh_at_agency.com> = ]=20
Sent: Friday, June 09, 2000 12:40 PM=20
To: Multiple recipients of list ORACLE-L=20 Subject: Re: Db_block_size=20

Eric Fang wrote:=20

>=20

> Thanks, Chris, Rachel and Guy for the answers.=20
> Actually we don't have production database(anytime),=20
> so I don't even have the archive log files. My=20
> question is what's the benefits of increasing the=20
> db_block_size, what is the limit?=20

As a rule of thumb, large block size are good for OLAP loads,=20 and small block sizes are good for OLTP. The actual sizing=20 depends on your OS block size. Oracle thinks in terms of=20 blocks when it does I/O. Therefore, if you can get an Oracle=20 block in an integral number of OS blocks, this is good. If=20 you have to read an entire OS block, but Oracle only wants=20 part of that to complete a data block, this is bad.=20

Cheers,=20

g=20

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