Horton

Re: Berserk Autovacuum (let's save next Mandrill)

Laurenz Albe <laurenz.albe@cybertec.at>

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From: Laurenz Albe <laurenz.albe@cybertec.at>
To: Justin Pryzby <pryzby@telsasoft.com>
Cc: Andres Freund <andres@anarazel.de>, Masahiko Sawada <masahiko.sawada@2ndquadrant.com>, David Rowley <dgrowleyml@gmail.com>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, Amit Kapila <amit.kapila16@gmail.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Darafei Komяpa Praliaskouski <me@komzpa.net>, pgsql-hackers@lists.postgresql.org, Alvaro Herrera <alvherre@2ndquadrant.com>, Michael Banck <mbanck@gmx.net>
Date: 2020-03-17T21:01:15Z
Lists: pgsql-hackers 
On Tue, 2020-03-17 at 14:56 -0500, Justin Pryzby wrote:
> I still suggest scale_factor maximum of 1e10, like
> 4d54543efa5eb074ead4d0fadb2af4161c943044
> 
> Which alows more effectively disabling it than a factor of 100, which would
> progress like: ~1, 1e2, 1e4, 1e6, 1e8, 1e10, ..
> 
> I don't think that 1e4 would be a problem, but 1e6 and 1e8 could be.  With
> 1e10, it's first vacuumed when there's 10billion inserts, if we didn't previous
> hit the n_dead threshold.
> 
> I think that's ok?  If one wanted to disable it up to 1e11 tuples, I think
> they'd disable autovacuum, or preferably just implement an vacuum job.

Assume a scale factor >= 1, for example 2, and n live tuples.
The table has just been vacuumed.

Now we insert m number tuples (which are live).

Then the condition

  threshold + scale_factor * live_tuples < newly_inserted_tuples

becomes

  10000000 + 2 * (n + m) < m

which can never be true for non-negative n and m.

So a scale factor >= 1 disables the feature.

Yours,
Laurenz Albe

Commits

  1. Further improve stability fix for partition_aggregate test.

  2. Improve stability fix for partition_aggregate test.

  3. Attempt to stabilize partitionwise_aggregate test

  4. Fix race condition in statext_store().

  5. Attempt to fix unstable regression tests, take 2

  6. Attempt to fix unstable regression tests

  7. Trigger autovacuum based on number of INSERTs

  8. Fix upper limit for vacuum_cleanup_index_scale_factor