Message-ID: <4F5B6F67.1040300@fuzzy.cz>
Date: Sat, 10 Mar 2012 16:12:39 +0100
From: Tomas Vondra <tv@fuzzy.cz>
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To: pgsql-performance@postgresql.org
Subject: Re: Comments requested on IO performance : new db server
References: <20120309111558.GA22643@campbell-lange.net>
	<20120310105112.GB9760@campbell-lange.net>
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On 10.3.2012 11:51, Rory Campbell-Lange wrote:
> Is a block size of 4096 a good idea both for the filesystem and
> postgresql? The analysis here:
> http://www.fuzzy.cz/en/articles/benchmark-results-hdd-read-write-pgbench/ 
> appears to suggest that at least for database block sizes of 4096
> read/write performance is much higher than for smaller block sizes.

Hi,

interpreting those results is a bit tricky for several reasons. First,
those are 'average results' for all filesystems (and the behavior of
filesystems may vary significantly). I'd recommend checking results for
the filesystem you're going to use (http://www.fuzzy.cz/bench)

Second, the article discusses just TPC-B (OLTP-like) workload results.
It's quite probable your workload is going to mix that with other
workload types (e.g. DSS/DWH). And that's exactly where larger block
sizes are better.

To me, 8kB seems like a good compromise. Don't use other block sizes
unless you actually test the benefits for your workload.

Tomas

> 
> Rory
> 
> On 09/03/12, Rory Campbell-Lange (rory@campbell-lange.net) wrote:
>> ...An ancillary question is whether a 4096 block size is a good idea.
>> I suppose we will be using XFS which I understand has a default block
>> size of 4096 bytes. 
>>
>> RAID 10
>> --------------------------------------
>> Read sequential
>>
>>     BS           MB/s             IOPs
>>    512        0129.26        264730.80
>>   1024        0229.75        235273.40
>>   4096        0363.14        092965.50
>>  16384        0475.02        030401.50
>>  65536        0472.79        007564.65
>> 131072        0428.15        003425.20
>> --------------------------------------
>> Write sequential
>>
>>     BS           MB/s             IOPs
>>    512        0036.08        073908.00
>>   1024        0065.61        067192.60
>>   4096        0170.15        043560.40
>>  16384        0219.80        014067.57
>>  65536        0240.05        003840.91
>> 131072        0243.96        001951.74
>> --------------------------------------
>> Random read
>>
>>     BS           MB/s             IOPs
>>    512        0001.50        003077.20
>>   1024        0002.91        002981.40
>>   4096        0011.59        002968.30
>>  16384        0044.50        002848.28
>>  65536        0156.96        002511.41
>> 131072        0170.65        001365.25
>> --------------------------------------
>> Random write
>>
>>     BS           MB/s             IOPs
>>    512        0000.53        001103.60
>>   1024        0001.15        001179.20
>>   4096        0004.43        001135.30
>>  16384        0017.61        001127.56
>>  65536        0061.39        000982.39
>> 131072        0079.27        000634.16
>> --------------------------------------