Re: Can checkpoint creation be parallel? - Mailing list pgsql-general
| From | 高健 |
|---|---|
| Subject | Re: Can checkpoint creation be parallel? |
| Date | |
| Msg-id | CAL454F2zUH+wO61JAsNJcJHWtwT_erSKA2yrm-GiCYBTJu1brQ@mail.gmail.com Whole thread Raw |
| In response to | Re: Can checkpoint creation be parallel? (Jeff Janes <jeff.janes@gmail.com>) |
| Responses |
Re: Can checkpoint creation be parallel?
|
| List | pgsql-general |
Thanks a lot for all your kindly replying!
>The background writer and ordinary backends might write data (for their own rea>sons) that the checkpointer would have otherwise needed to write anyway.
And does the ordinary backends refer to
the ones created when a client make a connection to PG?
For exampel:
When staring PG:
[root@pg200 ~]# ps -ef | grep post
root 3039 3015 0 11:02 pts/1 00:00:00 su - postgres
postgres 3040 3039 0 11:02 pts/1 00:00:00 -bash
postgres 3093 1 0 11:03 pts/1 00:00:00 /usr/local/pgsql/bin/postgres -D ./data
postgres 3095 3093 0 11:03 ? 00:00:00 postgres: checkpointer process
postgres 3096 3093 0 11:03 ? 00:00:00 postgres: writer process
postgres 3097 3093 0 11:03 ? 00:00:00 postgres: wal writer process
postgres 3098 3093 0 11:03 ? 00:00:00 postgres: autovacuum launcher process
postgres 3099 3093 0 11:03 ? 00:00:00 postgres: stats collector process
root 3126 3103 0 11:03 pts/2 00:00:00 grep post
After using psql to connect:
[root@pg200 ~]# ps -ef | grep post
root 3039 3015 0 11:02 pts/1 00:00:00 su - postgres
postgres 3040 3039 0 11:02 pts/1 00:00:00 -bash
postgres 3093 1 0 11:03 pts/1 00:00:00 /usr/local/pgsql/bin/postgres -D ./data
postgres 3095 3093 0 11:03 ? 00:00:00 postgres: checkpointer process
postgres 3096 3093 0 11:03 ? 00:00:00 postgres: writer process
postgres 3097 3093 0 11:03 ? 00:00:00 postgres: wal writer process
postgres 3098 3093 0 11:03 ? 00:00:00 postgres: autovacuum launcher process
postgres 3099 3093 0 11:03 ? 00:00:00 postgres: stats collector process
root 3150 3130 0 11:03 pts/3 00:00:00 su - postgres
postgres 3151 3150 0 11:03 pts/3 00:00:00 -bash
postgres 3183 3151 0 11:04 pts/3 00:00:00 ./psql
postgres 3184 3093 0 11:04 ? 00:00:00 postgres: postgres postgres [local] idle
root 3186 3103 0 11:04 pts/2 00:00:00 grep post
[root@pg200 ~]#
Does the above ordinary backends mean to the process 3184?
Best Regards
jian gao
2013/10/9 Jeff Janes <jeff.janes@gmail.com>
On Tue, Oct 8, 2013 at 1:54 AM, 高健 <luckyjackgao@gmail.com> wrote:Hello:
Sorry for disturbing:
I have one question about checkponint . That is : can checkpoint be parallel?
PostgreSQL does not currently implement it that way. And it is hard to see what the benefit would be of doing so. But it should be theoretically possible.It is said that checkpoint will be activated according to either conditions:
1)After last checkpoint, checkpoint_timeout seconds passed.
After the *start* of the last checkpoint. Provided that the last checkpoint has finished.2)When shared_buffers memory above checkpoint_segments size is filled with data.
It is not shared_buffers that is measured, but the WAL files themselves (which effectively means wal_buffers usage) that is measured.My experience is that :
There is only one checkpoint process there and works, and even when there are many data created during transactions,
There will also be only one checkpoint process deal with it
(maybe background writer or some other server process will deal it)?
The background writer and ordinary backends might write data (for their own reasons) that the checkpointer would have otherwise needed to write anyway.Cheers,Jeff
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