Re: Should vacuum process config file reload more often

On Fri, Mar 31, 2023 at 10:31 AM Melanie Plageman
<melanieplageman@gmail.com> wrote:
>
> On Thu, Mar 30, 2023 at 3:26 PM Daniel Gustafsson <daniel@yesql.se> wrote:
> >
> > > On 30 Mar 2023, at 04:57, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > > As another idea, why don't we use macros for that? For example,
> > > suppose VacuumCostStatus is like:
> > >
> > > typedef enum VacuumCostStatus
> > > {
> > >    VACUUM_COST_INACTIVE_LOCKED = 0,
> > >    VACUUM_COST_INACTIVE,
> > >    VACUUM_COST_ACTIVE,
> > > } VacuumCostStatus;
> > > VacuumCostStatus VacuumCost;
> > >
> > > non-vacuum code can use the following macros:
> > >
> > > #define VacuumCostActive() (VacuumCost == VACUUM_COST_ACTIVE)
> > > #define VacuumCostInactive() (VacuumCost <= VACUUM_COST_INACTIVE) //
> > > or we can use !VacuumCostActive() instead.
> >
> > I'm in favor of something along these lines.  A variable with a name that
> > implies a boolean value (active/inactive) but actually contains a tri-value is
> > easily misunderstood.  A VacuumCostState tri-value variable (or a better name)
> > with a set of convenient macros for extracting the boolean active/inactive that
> > most of the code needs to be concerned with would more for more readable code I
> > think.
>
> The macros are very error-prone. I was just implementing this idea and
> mistakenly tried to set the macro instead of the variable in multiple
> places. Avoiding this involves another set of macros, and, in the end, I
> think the complexity is much worse. Given the reviewers' uniform dislike
> of VacuumCostInactive, I favor going back to two variables
> (VacuumCostActive + VacuumFailsafeActive) and moving
> LVRelState->failsafe_active to the global VacuumFailsafeActive.
>
> I will reimplement this in the next version.
>
> On the subject of globals, the next version will implement
> Horiguchi-san's proposal to separate GUC variables from the globals used
> in the code (quoted below). It should hopefully reduce the complexity of
> this patchset.
>
> > Although it's somewhat unrelated to the goal of this patch, I think we
> > should clean up the code tidy before proceeding. Shouldn't we separate
> > the actual parameters from the GUC base variables, and sort out the
> > all related variaghble? (something like the attached, on top of your
> > patch.)

Attached is v12. It has a number of updates, including a commit to
separate VacuumCostLimit and VacuumCostDelay from the gucs
vacuum_cost_limit and vacuum_cost_delay, and a return to
VacuumCostActive.

- Melanie