Re: description of CHECKPOINT command confusing

On Wed, Oct 12, 2011 at 12:02 PM, Josh Kupershmidt <schmiddy(at)gmail(dot)com> wrote:
> Basically, I think the page should be structured to emphasize
>  1.) what is a "checkpoint" to a user who is not familiar with the term, and
>  2.) why would a user want to use the CHECKPOINT command?
>
> To tackle 1.), I think a little bit of reorganization along with a
> link to the right spot, namely:
>   http://www.postgresql.org/docs/current/static/wal-configuration.html
>
> will go a long way. I've attached an admittedly rough patch to try to
> address problem 1.).

+1

> As for 2.), there is no good answer on that page right now, other than
> "not intended for use during normal operation". Off the top of my
> head, the only suggested use I remember for CHECKPOINT is as a
> recommended step before pg_start_backup(); anyone know of other uses?
> And this bit:

It's for preventing pg_start_backup() from taking lots of time? If so,
you're right in 8.3 and before. In 8.4 and later, instead, you can specify
whether pg_start_backup() performs smoothed checkpoint or immediate
one, by using the second argument of pg_start_backup().

I'm not sure if there are other use cases during normal operation.

> | If executed during recovery, the CHECKPOINT command will
> | force a restartpoint rather than writing a new checkpoint.
>
> doesn't explain or link to what a "restartpoint" is, should it?

It's helpful to link to that. What a "restartpoint" is explained in also
http://www.postgresql.org/docs/current/static/wal-configuration.html

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center