On Thu, Oct 4, 2018 at 6:15 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Mon, Oct 1, 2018 at 7:20 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> >
> > Hi,
> >
> > Attached patch adds a new option FREEZE_ONLY to VACUUM command. This
> > option is same as FREEZE option except for it disables reclaiming dead
> > tuples. That is, with this option vacuum does pruning HOT chain,
> > freezing live tuples and maintaining both visibility map and freespace
> > map but does not collect dead tuples and invoke neither heap vacuum
> > nor index vacuum. This option will be useful if user wants to prevent
> > XID wraparound a table as quick as possible, especially when table is
> > quite large and is about to XID wraparound. I think this usecase was
> > mentioned in some threads but I couldn't find them.
> >
> > Currently this patch just adds the new option to VACUUM command but it
> > might be good to make autovacuum use it when emergency vacuum is
> > required.
> >
> > This is a performance-test result for FREEZE option and FREEZE_ONLY
> > option. I've tested them on the table which is about 3.8GB table
> > without indexes and randomly modified.
> >
> > * FREEZE
> > INFO: aggressively vacuuming "public.pgbench_accounts"
> > INFO: "pgbench_accounts": removed 5 row versions in 8 pages
> > INFO: "pgbench_accounts": found 5 removable, 30000000 nonremovable
> > row versions in 491804 out of 491804 pages
> > DETAIL: 0 dead row versions cannot be removed yet, oldest xmin: 722
> > There were 0 unused item pointers.
> > Skipped 0 pages due to buffer pins, 0 frozen pages.
> > 0 pages are entirely empty.
> > CPU: user: 4.20 s, system: 16.47 s, elapsed: 50.28 s.
> > VACUUM
> > Time: 50301.262 ms (00:50.301)
> >
> > * FREEZE_ONLY
> > INFO: aggressively vacuuming "public.pgbench_accounts"
> > INFO: "pgbench_accounts": found 4 removable, 30000000 nonremovable
> > row versions in 491804 out of 491804 pages
> > DETAIL: freeze 30000000 rows
> > There were 0 unused item pointers.
> > Skipped 0 pages due to buffer pins, 0 frozen pages.
> > 0 pages are entirely empty.
> > CPU: user: 3.10 s, system: 14.85 s, elapsed: 44.56 s.
> > VACUUM
> > Time: 44589.794 ms (00:44.590)
> >
> > Feedback is very welcome.
> >
>
> Added to the next commit fest.
Rebaed to the current HEAD.
Regards,
--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center