On 24/10/13 12:46, Josh Berkus wrote:
> On 10/23/2013 01:26 PM, Peter Geoghegan wrote:
>> So fixing that problem would go a long
>> way towards resolving these concerns. It would also probably have the
>> benefit of making it possible for query texts to be arbitrarily long -
>> we'd be storing them in files (with a shared memory buffer). I get a
>> lot of complaints about the truncation of query texts in
>> pg_stat_statements, so I think that'd be really valuable. It would
>> make far higher pg_stat_statements.max values practical to boot, by
>> radically reducing the amount of shared memory required.
>>
>> All of this might be a bit tricky, but I suspect it's well worth it.
> So you're suggesting that instead of storing the aggregates as we
> currently do, we store a buffer of the last N queries (in normal form)
> and their stats? And then aggregate when the user asks for it?
>
> That would be nice, and IMHO the only way we can really resolve all of
> these stats concerns. Any approach we take using histograms etc. is
> going to leave out some stat someone needs.
>
I don't see it as as either/or.
It might be useful to optionally all the last n queries be stored as you
suggested. People could decide for themselves how much storage they are
willing to allocate for the purpose.
Storing the last n queries, could be helpful in seeing why some users
are suddenly experiencing very slow response times.
I think the histogram would be more useful over a day or a week.
Cheers,
Gavin
