Re: Maximum transaction rate

Scott Marlowe wrote:
> On Fri, Mar 6, 2009 at 2:22 PM, Ben Chobot <bench(at)silentmedia(dot)com> wrote:
>> On Fri, 6 Mar 2009, Greg Smith wrote:
>>
>>> On Fri, 6 Mar 2009, Tom Lane wrote:
>>>
>>>> Otherwise you need to reconfigure your drive to not cache writes.
>>>> I forget the incantation for that but it's in the PG list archives.
>>> There's a dicussion of this in the docs now,
>>> http://www.postgresql.org/docs/8.3/interactive/wal-reliability.html
>> How does turning off write caching on the disk stop the problem with LVM? It
>> still seems like you have to get the data out of the OS buffer, and if
>> fsync() doesn't do that for you....
>
> I think he was saying otherwise (if you're not using LVM and you still
> have this super high transaction rate) you'll need to turn off the
> drive's write caches. I kinda wondered at it for a second too.
>

And I'm still wondering. The problem with LVM, AFAIK, is missing support
for write barriers. Once you disable the write-back cache on the disk,
you no longer need write barriers. So I'm missing something, what else
does LVM do to break fsync()?

It was my understanding that disabling disk caches was enough.

.TM.