On Jul 7, 2012, at 8:54 AM, Magnus Hagander <mag...@hagander.net> wrote:
> On Sat, Jul 7, 2012 at 3:52 PM, Robert Haas <robertmh...@gmail.com> wrote:
>> On Jul 7, 2012, at 9:07 AM, Euler Taveira <eu...@timbira.com> wrote:
>>> On 07-07-2012 09:00, Satoshi Nagayasu wrote:
>>>> I've created new patch to get/reset statistics of WAL buffer
>>>> writes (flushes) caused by WAL buffer full.
>>> This new statistic doesn't solve your problem (tune wal_buffers). It doesn't
>>> give you the wal_buffers value. It only says "hey, I needed more buffers so 
>>> I
>>> write those dirty ones". It doesn't say how many. I would like to have
>>> something that says "hey, you have 1000 buffers available and  you are using
>>> 100 buffers (10%)". This new statistic is only useful for decreasing the
>>> WALWriteLock contention.
>> The number of WAL buffers that you are using is going to change so quickly 
>> as to be utterly meaningless.  I don't really see that there's any statistic 
>> we could gather that would tell us how many WAL buffers are needed.  This 
>> patch seems like it's on the right track, at least telling you how often 
>> you're running out.
> We could keep a high watermark of "what's the largest percentage we've
> used", perhaps?

Sure, but I doubt that would be as informative as this.  It's no big deal if 
you hit 100% every once in a while; what you really want to know is whether 
it's happening once per second or once per week.

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