RE: Db_block_size

From: Sandeep Kurliye <Sandeep.Kurliye_at_almarai.com>
Date: Tue, 1 Aug 2000 10:00:53 +0300
Message-Id: <10576.113452@fatcity.com>

When you issue command 'df -k', it gives you operating system block size in header.

This is an observation on AIX 4.3.2.

Sandeep.

	-----Original Message-----
	From:	Subramaniam, Lakshmi (L.) [SMTP:lsubrama_at_ford.com]
	Sent:	Thursday, July 20, 2000 2:15 AM
	To:	Multiple recipients of list ORACLE-L
	Subject:	RE: Db_block_size

	How do we find the operating system block size on unix?
	 
	Lakshmi
	-----Original Message-----
	From: Alex Hillman [mailto:alex_hillman_at_physia.com]
	Sent: Friday, June 09, 2000 6:49 PM
	To: Multiple recipients of list ORACLE-L
	Subject: 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	Maybe this rule of thumb a little outdated.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

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


	Eric Fang wrote: 


	> 

	> Thanks, Chris, Rachel and Guy for the answers. 

	> Actually we don't have production database(anytime), 

	> so I don't even have the archive log files. My 

	> question is what's the benefits of increasing the 

	> db_block_size, what is the limit? 


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

	Cheers, 

	g 



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Received on Tue Aug 01 2000 - 02:00:53 CDT