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.
Regards,
--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center
