Re: Interpreting autovacuum logs (9.6)

On 6/26/20 11:47 AM, Gabe Kopley wrote:
> Hi all,
>
> Please see this graph of data points extracted from autovacuum logs:
> https://imgur.com/a/OCRKoDn . It's from a 9.6 instance with default
> params for autovacuum with the exceptions of autovacuum_work_mem=10000
> and log_autovacuum_min_duration=100.
>
> 1. How should we interpret the # tuples remain reported by the autovac
> logs? The source code says it's the "estimated total # of tuples" which
> to me means # dead + # live. But that is invalidated by the pattern here
> where the orange points (# tuples remain) are dramatically higher than #
> dead not removable (blue points) + # dead removed (green points) + #
> live (which never exceeded 1M during this entire interval, per count query).
>
> 2. Beginning around the first 6/19 tick, what could be causing # tuples
> remain to drop steeply after periods of growth when # tuples removed is
> 0? I confirmed there was no truncation. And what could the # tuples
> remain recurrent asymptote at ~22M mean?

AFAIK there is not dedicated autovac log, so something is pulling this
out of the Postgres log correct?

What is the program that is doing that and what is the raw output?

>
> (further context for those curious: the discontinuity at 6/23 is due to
> an individual autovacuum run getting stuck. After manually killing that
> run, the next one succeeded and you see that reporting toward the right
> of the graph)
>
> Thanks!
>
> Gabe
>
>

--
Adrian Klaver
adrian(dot)klaver(at)aklaver(dot)com