On Mon, Oct 1, 2018 at 7:20 PM Masahiko Sawada <sawada.m...@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
