Horton

Re: Should we increase the default vacuum_cost_limit?

David Rowley <david.rowley@2ndquadrant.com>

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From: David Rowley <david.rowley@2ndquadrant.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Jeff Janes <jeff.janes@gmail.com>, Andrew Dunstan <andrew.dunstan@2ndquadrant.com>, Jeremy Schneider <schnjere@amazon.com>, Joe Conway <mail@joeconway.com>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-08T23:47:34Z
Lists: pgsql-hackers 
On Sat, 9 Mar 2019 at 07:10, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Jeff Janes <jeff.janes@gmail.com> writes:
> > Now that this is done, the default value is only 5x below the hard-coded
> > maximum of 10,000.
> > This seems a bit odd, and not very future-proof.  Especially since the
> > hard-coded maximum appears to have no logic to it anyway, at least none
> > that is documented.  Is it just mindless nannyism?
>
> Hm.  I think the idea was that rather than setting it to "something very
> large", you'd want to just disable the feature via vacuum_cost_delay.
> But I agree that the threshold for what is ridiculously large probably
> ought to be well more than 5x the default, and maybe it is just mindless
> nannyism to have a limit less than what the implementation can handle.

Yeah, +1 to increasing it.  I imagine that the 10,000 limit would not
allow people to explore the upper limits of a modern PCI-E SSD with
the standard delay time and dirty/miss scores.  Also, it doesn't seem
entirely unreasonable that someone somewhere might also want to
fine-tune the hit/miss/dirty scores so that they're some larger factor
apart from each other the standard scores are. The 10,000 limit does
not allow much wiggle room for that.

-- 
 David Rowley                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Commits

  1. Allow fractional input values for integer GUCs, and improve rounding logic.

  2. Reduce the default value of autovacuum_vacuum_cost_delay to 2ms.

  3. Revert "Increase the default vacuum_cost_limit from 200 to 2000"

  4. Convert [autovacuum_]vacuum_cost_delay into floating-point GUCs.

  5. Include GUC's unit, if it has one, in out-of-range error messages.

  6. Disallow NaN as a value for floating-point GUCs.

  7. Increase the default vacuum_cost_limit from 200 to 2000