Re: WAL segments (names) not in a sequence
| От | German Becker |
|---|---|
| Тема | Re: WAL segments (names) not in a sequence |
| Дата | |
| Msg-id | CALyjCLvem97TbuTq0ZihYurfwetW5qz5fOVa80kSnXdxPO6a9g@mail.gmail.com обсуждение исходный текст |
| Ответ на | Re: WAL segments (names) not in a sequence (Amit Langote <amitlangote09@gmail.com>) |
| Список | pgsql-hackers |
On Fri, May 24, 2013 at 3:24 PM, Amit Langote <amitlangote09@gmail.com> wrote:
On Sat, May 25, 2013 at 3:08 AM, German Becker <german.becker@gmail.com> wrote:Upthread, Fujii Masao-san suggested what might have happened that
> Thanks Amit, I understand now. Is there a way to know/predict how many
> prealocated segments will there be in a certain moment? What does it deppend
> on?
caused these pre-allocated segments to be created. To quote him:Reading here would also help:
"WAL recycling is performed by checkpoint. Checkpoint always checks
whether there are WAL files no longer required for crash recovery,
IOW, WAL files which were generated before the prior checkpoint
happened, and then if they are found, checkpoint tries to recycle
them."
http://www.postgresql.org/docs/9.1/static/wal-configuration.html
If you are still using the same values as during this observation,
could you provide values for these postgresql.conf parameters:
checkpoint_segments, checkpoint_timeout, wal_keep_segments?
--
Amit Langote
Amit,
Frist, thanks for your help and your interest. I (think) I understand how checkpoint /wal segment work. What I didn't understand from the documentation is the possibility of segments being prealocated. I thought that the WAL segment with the higher sequence number is the one being written at present time, as opposed to a segment allocated to be written in the future. If you could clarify this point to me, that would be great.
Here are the parameters related to checkpoint
For "restore" config
checkpoint_segments = 256 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 5min # range 30s-1h
#checkpoint_completion_target = 0.5 # checkpoint target duration, 0.0 - 1.0
#checkpoint_warning = 30s
#wal_keep_segments = 0 # in logfile segments, 16MB each; 0 disables
For "production" config:
checkpoint_segments = 256 # in logfile segments, min 1, 16MB each
#checkpoint_timeout = 5min # range 30s-1h
checkpoint_completion_target = 0.7 # checkpoint target duration, 0.0 - 1.0
wal_keep_segments = 256 # in logfile segments, 16MB each; 0 disables
Thanks again,
Germán
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