On Tue, Jul 25, 2017 at 2:27 AM, Claudio Freire <klaussfre...@gmail.com> wrote: > On Mon, Jul 24, 2017 at 2:20 PM, Claudio Freire <klaussfre...@gmail.com> > wrote: >> On Mon, Jul 24, 2017 at 2:10 PM, Sokolov Yura >> <funny.fal...@postgrespro.ru> wrote: >>> On 2017-07-24 19:11, Claudio Freire wrote: >>>> I was mostly thinking about something like the attached patch. >>>> >>>> Simple, unintrusive, and shouldn't cause any noticeable slowdown. >>> >>> >>> Your change is small, clear, and currently useful for huge tables under >>> high update load (until "allowing vacuum to use more than 1GB memory" >>> is merged). >> >> In high-bloat conditions, it doesn't take long to accumulate 1GB of >> dead tuples (which is about 178M tuples, btw). >> >> The index scan takes way longer than the heap scan in that case. >> >>> But it still delays updating fsm until whole first batch of dead tuples >>> cleared (ie all indices scanned, and all heap pages cleared), and on such >>> huge table it will be hours. >> >> So, true, it will get delayed considerably. But as you realized, >> there's not much point in trying to vacuum the FSM sooner, since it >> won't be accurate shortly afterwards anyway. Dead line pointers do use >> up a fair bit of space, especially on narrow tables. >> >> In a particular table I have that exhibits this problem, most of the >> time is spent scanning the index. It performs dozens of index scans >> before it's done, so it would vacuum the FSM quite often enough, even >> if I were to increase the mwm setting n-fold. > > I hate to reply to myself, but I wanted to add: in any case, the case > I'm trying to avoid is the case where the FSM *never* gets vacuumed. > That's bad. But it may not be the phenomenon you're experiencing in > your tests. >
I think the frequently vacuuming the FSM during long-time vacuum would be worth to have in order to avoid a table bloating. The patch triggers to vacuum the FSM after vacuumed the table and indexes but I think that we can have a similar mechanism for a table with no index. Regards, -- Masahiko Sawada NIPPON TELEGRAPH AND TELEPHONE CORPORATION NTT Open Source Software Center -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers