Re: BUG #10675: alter database set tablespace and unlogged table

On 18 June 2014 14:45, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
>> On 2014-06-18 16:15:47 +0530, Pavan Deolasee wrote:
>>> But I wonder if not flushing dirty buffers
>>> of unlogged tables at a checkpoint is a bad idea anyways. User might expect
>>> that the unlogged tables to sustain server crash or unclean shutdown if
>>> there had been no writes after successful manual checkpoint(s).
>
>> They'll get reset at unlcean startup anyway. Independent of having been
>> touched or not.
>
> I'm with Pavan on this one: it's *not* a good thing that manually issued
> checkpoints skip unlogged tables.  That's surprising, possibly dangerous,
> and no case whatsoever has been made that anyone sees it as an important
> performance benefit.
>
> I trust that a shutdown checkpoint, at least, would write such pages?
> If so, I'd expect that a manual checkpoint would do it too.  Maybe
> I'm checkpointing because I want to be sure that the shutdown will be
> quick so I can do a minor release update with minimal downtime.

I think manual checkpoints should flush everything.

This is a valid use case.

What other use case is there for a manual checkpoint?


> I think we should just change this.  -1 for new flags and more
> complication.

--
 Simon Riggs                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services