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: 2019-03-10T13:10:43Z
Lists: pgsql-hackers 
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?
 We need a backward-compatible format for vacuum setting, but I don't
see a good reason to force external extensions to do the same, and it
wouldn't require much extra work.

> The second converts [autovacuum_]cost_delay to float GUCs, and changes
> the default value for autovacuum_cost_delay from 20ms to 2ms.
> We'd want to revert the previous patch that changed the default value
> of vacuum_cost_limit, else this means a 100x not 10x change in the
> default autovac speed ... but I've not included that in this patch.

Otherwise everything looks good to me.  BTW the patches didn't apply
cleanly with git-apply, but patch -p1 didn't complain.

> 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.

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