Re: Can checkpoint creation be parallel?

On Tue, Oct 8, 2013 at 1:54 AM, 高健 <luckyjackgao(at)gmail(dot)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