Re: Re: PATCH: Split stats file per database WAS: autovacuum stress-testing our system

Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> writes:
> On 05/26/2016 10:10 PM, Tom Lane wrote:
>> In view of 52e8fc3e2, there's more or less no case in which we'd be
>> writing stats without writing stats for the shared catalogs. So I'm
>> tempted to propose that we try to reduce the overhead by merging the
>> shared-catalog stats back into the global-stats file, thereby
>> halving the filesystem metadata traffic for updating those.

> I find this a bit contradictory with the previous paragraph. If you
> believe that reducing the filesystem metadata traffic will have a
> measurable benefit, then surely merging writes for multiple dbs (thus
> not writing the global/shared files multiple times) will have even
> higher impact, no?

Well, my thinking is that this is something we could get "for free"
without any penalty in response time. Going further will require
some sort of tradeoff.

regards, tom lane