Horton

Re: Should we increase the default vacuum_cost_limit?

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Julien Rouhaud <rjuju123@gmail.com>
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: 2019-03-10T15:47:17Z
Lists: pgsql-hackers 
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.)

>> 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.

			regards, tom lane

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