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Re: which ext3 fs type should I use for postgresql

From: david(at)lang(dot)hm
To: Matthew Wakeling <matthew(at)flymine(dot)org>
Cc: "pgsql-performance(at)postgresql(dot)org" <pgsql-performance(at)postgresql(dot)org>
Subject: Re: which ext3 fs type should I use for postgresql
Date: 2008-05-16 09:58:08
Message-ID: alpine.DEB.1.10.0805160257360.21812@asgard (view raw, whole thread or download thread mbox)
Lists: pgsql-performance
On Thu, 15 May 2008, david(at)lang(dot)hm wrote:

> On Thu, 15 May 2008, Matthew Wakeling wrote:
>> On Thu, 15 May 2008, Philippe Amelant wrote:
>>> using mkfs.ext3 I can use "-T" to tune the filesytem
>>> mkfs.ext3 -T fs_type ...
>>> fs_type are in /etc/mke2fs.conf (on debian)
>> If you look at that file, you'd see that tuning really doesn't change that 
>> much. In fact, the only thing it does change (if you avoid "small" and 
>> "floppy") is the number of inodes available in the filesystem. Since 
>> Postgres tends to produce few large files, you don't need that many inodes, 
>> so the "largefile" option may be best. However, note that the number of 
>> inodes is a hard limit of the filesystem - if you try to create more files 
>> on the filesystem than there are available inodes, then you will get an out 
>> of space error even if the filesystem has space left.
>> The only real benefit of having not many inodes is that you waste a little 
>> less space, so many admins are pretty generous with this setting.
> IIRC postgres likes to do 1M/file, which isn't very largeas far as the -T 
> setting goes.
>> Probably of more use are some of the other settings:
>> -m reserved-blocks-percentage - this reserves a portion of the filesystem
>>    that only root can write to. If root has no need for it, you can kill
>>    this by setting it to zero. The default is for 5% of the disc to be
>>    wasted.
> think twice about this. ext2/3 get slow when they fill up (they have 
> fragmentation problems when free space gets too small), this 5% that only 
> root can use also serves as a buffer against that as well.
>> -j turns the filesystem into ext3 instead of ext2 - many people say that
>>    for Postgres you shouldn't do this, as ext2 is faster.
> for the partition with the WAL on it you may as well do ext2 (the WAL is 
> written synchronously and sequentially so the journal doesn't help you), but 
> for the data partition you may benifit from the journal.

a fairly recent article on the subject

David Lang

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