Horton

Re: Should we increase the default vacuum_cost_limit?

Julien Rouhaud <rjuju123@gmail.com>

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From: Julien Rouhaud <rjuju123@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Andrew Dunstan <andrew.dunstan@2ndquadrant.com>, David Rowley <david.rowley@2ndquadrant.com>, Jeff Janes <jeff.janes@gmail.com>, Jeremy Schneider <schnjere@amazon.com>, Joe Conway <mail@joeconway.com>, Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2019-03-10T15:56:34Z
Lists: pgsql-hackers 
On Sun, Mar 10, 2019 at 4:47 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Julien Rouhaud <rjuju123@gmail.com> writes:
> > On Sat, Mar 9, 2019 at 10:04 PM Tom Lane <tgl@sss.pgh.pa.us> wrote:
> >> I tried this, and it seems to work pretty well.  The first of the two
> >> attached patches just teaches guc.c to support units for float values,
> >> incidentally allowing "us" as an input unit for time-based GUCs.
>
> > Why not allowing third party extensions to declare a GUC stored in us?
>
> I think that adding a new base unit type (GUC_UNIT_US) is possible but
> I'm disinclined to do it on the basis of zero evidence that it's needed.
> Only three of the five already-known time units are allowed to be base
> units (ms, s, min are but d and h aren't) so it's not like there's no
> precedent for excluding this one.  Anyway, such a patch would be mostly
> orthogonal to what I've done here, so it should be considered on its
> own merits.
> (BTW, if we're expecting to have GUCs that are meant to measure only
> very short time intervals, maybe it'd be more forward-looking for
> their base unit to be NS not US.)

That's fair.

> >> 2. It's always bugged me that we don't allow fractional unit
> >> specifications, say "0.1GB", even for GUCs that are integers underneath.
> >> That would be a simple additional change on top of this, but I didn't
> >> do it here.
>
> > It annoyed me multiple times, so +1 for making that happen.
>
> OK, will do.

Thanks!

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