Re: Publish autovacuum informations

On 3/1/16 8:37 AM, Julien Rouhaud wrote:
>> >
>> >We understood (IMHO is an interesting idea) but as Michael said hooks is
>> >for a general purpose. So can you demonstrate other use cases for this
>> >new hooks?
>> >
> I can think of several usage.  First, since the hook will always be
> called, an extension will see all the activity a worker is doing when
> exposing private structure will always be some kind of sampling.  Then,

I think that's pretty key. If you wanted to create an extension that 
logs vacuums (which would be great, since current state of the art is 
logs + pgBadger), you'd want to gather your data about what the vacuum 
did as the vacuum was ending.

I can certainly see cases where you don't care about that and just want 
what's in shared memory, but that would only be useful for monitoring 
what's happening real-time, not for knowing what final results are.

BTW, I think as much of this as possible should also work for regular 
vacuums.

> you can have other information that wouldn't be available just by
> exposing private structure.  For instance knowing a VACUUM isn't
> performed by the worker (either because another worker is already
> working on it or because it isn't needed anymore). IIRC there was a
> discussion about concurrency issue in this case. We can also know if the
> maintenance was cancelled due to lock not obtained fast enough.
> Finally, as long as the hooks aren't use, they don't have any overhead.
>   I agree that all this is for monitoring purpose.
>
> I'm not sure what are the fancy things that Michael had in mind with
> exposing the private structure.  Michael, was it something like having
> the ability to change some of these data through an extension?
-- 
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com