Re: [HACKERS] Block level parallel vacuum

On Tue, 12 Nov 2019 at 20:11, Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Tue, Nov 12, 2019 at 3:39 PM Masahiko Sawada
> <masahiko.sawada@2ndquadrant.com> wrote:
> >
> > On Tue, 12 Nov 2019 at 18:26, Dilip Kumar <dilipbalaut@gmail.com> wrote:
> > >
> > > On Tue, Nov 12, 2019 at 2:25 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > >
> > > > Yeah, maybe something like amparallelvacuumoptions.  The options can be:
> > > >
> > > > VACUUM_OPTION_NO_PARALLEL   0 # vacuum (neither bulkdelete nor
> > > > vacuumcleanup) can't be performed in parallel
> > > > VACUUM_OPTION_NO_PARALLEL_CLEANUP  1 # vacuumcleanup cannot be
> > > > performed in parallel (hash index will set this flag)
> > >
> > > Maybe we don't want this option?  because if 3 or 4 is not set then we
> > > will not do the cleanup in parallel right?
> > >
>
> Yeah, but it is better to be explicit about this.

VACUUM_OPTION_NO_PARALLEL_BULKDEL is missing? I think brin indexes
will use this flag. It will end up with
(VACUUM_OPTION_NO_PARALLEL_CLEANUP |
VACUUM_OPTION_NO_PARALLEL_BULKDEL) is equivalent to
VACUUM_OPTION_NO_PARALLEL, though.

>
> > > > VACUUM_OPTION_PARALLEL_BULKDEL   2 # bulkdelete can be done in
> > > > parallel (Indexes nbtree, hash, gin, gist, spgist, bloom will set this
> > > > flag)
> > > > VACUUM_OPTION_PARALLEL_COND_CLEANUP  3 # vacuumcleanup can be done in
> > > > parallel if bulkdelete is not performed (Indexes nbtree, brin, hash,
> > > > gin, gist, spgist, bloom will set this flag)
> > > > VACUUM_OPTION_PARALLEL_CLEANUP  4 # vacuumcleanup can be done in
> > > > parallel even if bulkdelete is already performed (Indexes gin, brin,
> > > > and bloom will set this flag)
> > > >
> > > > Does something like this make sense?
> >
> > 3 and 4 confused me because 4 also looks conditional. How about having
> > two flags instead: one for doing parallel cleanup when not performed
> > yet (VACUUM_OPTION_PARALLEL_COND_CLEANUP) and another one for doing
> > always parallel cleanup (VACUUM_OPTION_PARALLEL_CLEANUP)?
> >
>
> Hmm, this is exactly what I intend to say with 3 and 4.  I am not sure
> what makes you think 4 is conditional.

Hmm so why gin and bloom will set 3 and 4 flags? I thought if it sets
4 it doesn't need to set 3 because 4 means always doing cleanup in
parallel.

>
> > That way, we
> > can have flags as follows and index AM chooses two flags, one from the
> > first two flags for bulk deletion and another from next three flags
> > for cleanup.
> >
> > VACUUM_OPTION_PARALLEL_NO_BULKDEL 1 << 0
> > VACUUM_OPTION_PARALLEL_BULKDEL 1 << 1
> > VACUUM_OPTION_PARALLEL_NO_CLEANUP 1 << 2
> > VACUUM_OPTION_PARALLEL_COND_CLEANUP 1 << 3
> > VACUUM_OPTION_PARALLEL_CLEANUP 1 << 4
> >
>
> This also looks reasonable, but if there is an index that doesn't want
> to support a parallel vacuum, it needs to set multiple flags.

Right. It would be better to use uint16 as two uint8. I mean that if
first 8 bits are 0 it means VACUUM_OPTION_PARALLEL_NO_BULKDEL and if
next 8 bits are 0 means VACUUM_OPTION_PARALLEL_NO_CLEANUP. Other flags
could be followings:

VACUUM_OPTION_PARALLEL_BULKDEL 0x0001
VACUUM_OPTION_PARALLEL_COND_CLEANUP 0x0100
VACUUM_OPTION_PARALLEL_CLEANUP 0x0200

--
Masahiko Sawada            http://www.2ndQuadrant.com/
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