Re: how to measure wal_buffer usage

Lonni J Friedman wrote:
>>> After reading this interesting article on shared_buffers and wal_buffers:
>>> http://rhaas.blogspot.com/2012/03/tuning-sharedbuffers-and-walbuffers.html
>>>
>>> it got me wondering if my settings were ideal.  Is there some way to
>>> measure wal_buffer usage in real time, so that I could simply monitor
>>> it for some period of time, and then come up with a way of determining
>>> if the current setting is sufficient?
>>>
>>> I tried googling, but every reference that I've found simply defaults
>>> to the "trial & error" approach to performance tuning.
>>
>> You can use the contrib module pg_buffercache to inspect the shared buffers.
>> If almost all your shared buffers have high use count (4 or 5),
>> shared_buffers may be too small.  If not, consider reducing shared_buffers.
> 
> pg_buffercache only reports on the buffer_cache, it does not report
> any data on the wal_cache.

You are right.

>> It's probably better to start with a moderate value and tune upwards.
>>
>> You can also look at pg_statio_all_tables and pg_statio_all_indexes and
>> calculate the buffer hit ratio.  If that is low, that's also an indication
>> that shared_buffers is too small.
>
> Isn't this also specific to the buffer_cache rather than the wal_cache?

Correct.

I don't know how to inspect usage WAL cache usage.

Yours,
Laurenz Albe