Re: [PROPOSAL] VACUUM Progress Checker.

On 2015/12/11 14:41, Kyotaro HORIGUCHI wrote:
> Sorry, I misunderstood the meaning of PgStat_*.

I should've just said "messages to the stats collector" instead of
"PgStat_Msg's".

>
> At Fri, 11 Dec 2015 09:41:04 +0900, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> wrote
>>> As far as I understand it, the basic reason why this patch exists is
>>> to allow a DBA to have a hint of the progress of a VACUUM that may be
>>> taking minutes, or say hours, which is something we don't have now. So
>>> it seems perfectly fine to me to report this information
>>> asynchronously with a bit of lag. Why would we need so much precision
>>> in the report?
>>
>> Sorry, I didn't mean to overstate this requirement. I agree precise
>> real-time reporting of progress info is not such a stringent requirement
>> from the patch. The point regarding whether we should storm the collector
>> with progress info messages still holds, IMHO.
>
> Taking a few seconds interval between each messages would be
> sufficient. I personaly think that gettimeofday() per processing
> every buffer (or few buffers) is not so heavy-weight but I
> suppose there's not such a consensus here. However,
> IsCheckpointOnSchedule does that per writing one buffer.
>
> vacuum_delay_point() seems to be a reasonable point to check the
> interval and send stats since it would be designed to be called
> with the interval also appropriate for this purpose.

Interesting, vacuum_delay_point() may be worth considering.

It seems though that, overall, PgBackendStatus approach may be more suited
for progress tracking. Let's see what the author thinks.

Thanks,
Amit