Re: increasing the default WAL segment size
От | Tsunakawa, Takayuki |
---|---|
Тема | Re: increasing the default WAL segment size |
Дата | |
Msg-id | 0A3221C70F24FB45833433255569204D1F5E0D5B@G01JPEXMBYT05 обсуждение исходный текст |
Ответ на | increasing the default WAL segment size (Robert Haas <robertmhaas@gmail.com>) |
Список | pgsql-hackers |
> From: pgsql-hackers-owner@postgresql.org > [mailto:pgsql-hackers-owner@postgresql.org] On Behalf Of Robert Haas > Considering those three factors, I think we should consider pushing the > default value up somewhat higher for v10. Reverting to the 64MB size that > we had prior to 47937403676d913c0e740eec6b85113865c6c8ab > sounds pretty reasonable. +1 The other downside is that the response time of transactions may degrade when they have to wait for a new WAL segment tobe created. Tha might pop up as occasional slow or higher maximum response time, which is a mystery to users. Maybe it'stime to use posix_fallocate() to create WAL segments. > Possibly it would make sense for this to be configurable at initdb time > instead of requiring a recompile; we probably don't save any significant > number of cycles by compiling this into the server. +1 > 3. archive_timeout is no longer a frequently used option. Obviously, if > you are frequently archiving partial segments, you don't want the segment > size to be too large, because if it is, each forced segment switch > potentially wastes a large amount of space (and bandwidth). > But given streaming replication and pg_receivexlog, the use case for > archiving partial segments is, at least according to my understanding, a > lot narrower than it used to be. So, I think we don't have to worry as > much about keeping forced segment switches cheap as we did during the 8.x > series. I'm not sure about this. I know (many or not) users use continuous archiving with archive_command and archive_timeout forbackups, and don't want to use streaming replication, because the system is not worth the cost and trouble of HA. I heardfrom a few users that they were surprised when they knew that PostgreSQL generates WAL even when no update transactionis happening. Is this still true? Regards Takayuki Tsunakawa
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