Re: How filesystems matter with PostgreSQL

On Sat, Jun 5, 2010 at 5:03 PM, Jon Schewe <jpschewe(at)mtu(dot)net> wrote:
>
>
> On 06/05/2010 05:52 PM, Greg Smith wrote:
>> Jon Schewe wrote:
>>>>   If that's the case, what you've measured is which filesystems are
>>>> safe because they default to flushing drive cache (the ones that take
>>>> around 15 minutes) and which do not (the ones that take >=around 2
>>>> hours).  You can't make ext3 flush the cache correctly no matter what
>>>> you do with barriers, they just don't work on ext3 the way PostgreSQL
>>>> needs them to.
>>>>
>>>>
>>> So the 15 minute runs are doing it correctly and safely, but the slow
>>> ones are doing the wrong thing? That would imply that ext3 is the safe
>>> one. But your last statement suggests that ext3 is doing the wrong
>>> thing.
>>>
>>
>> I goofed and reversed the two times when writing that.  As is always
>> the case with this sort of thing, the unsafe runs are the fast ones.
>> ext3 does not ever do the right thing no matter how you configure it,
>> you have to compensate for its limitations with correct hardware setup
>> to make database writes reliable.
>>
> OK, so if I want the 15 minute speed, I need to give up safety (OK in
> this case as this is just research testing), or see if I can tune
> postgres better.

Or use a trustworthy hardware caching battery backed RAID controller,
either in RAID mode or JBOD mode.