On Tue, Jun 19, 2018 at 2:33 AM, Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> I think that we do the partial lazy vacuum using visibility map even
> now. That does heap pruning, index tuple killing but doesn't advance
> relfrozenxid.
Right, that's what I was thinking. Opportunistic HOT pruning isn't
like vacuuming because it doesn't touch indexes. This patch adds an
alternative strategy for conventional lazy vacuum that is also able to
run a page at a time if needed. Perhaps page-at-a-time operation could
later be used for doing something that is opportunistic in the same
way that pruning is opportunistic, but it's too early to worry about
that.
> Since this patch adds an ability to delete small amount
> of index tuples quickly, what I'd like to do with this patch is to
> invoke autovacuum more frequently, and do the target index deletion or
> the index bulk-deletion depending on amount of garbage and index size
> etc. That is, it might be better if lazy vacuum scans heap in ordinary
> way and then plans and decides a method of index deletion based on
> costs similar to what query planning does.
That seems to be what Andrey wants to do, though right now the
prototype patch actually just always uses its alternative strategy
while doing any kind of lazy vacuuming (some simple costing code is
commented out right now). It shouldn't be too hard to add some costing
to it. Once we do that, and once we polish the patch some more, we can
do performance testing. Maybe that alone will be enough to make the
patch worth committing; "opportunistic microvacuuming" can come later,
if at all.
--
Peter Geoghegan