Re: Fast promotion, loose ends

On 24.04.2013 11:23, Simon Riggs wrote:
> On 24 April 2013 09:10, Heikki Linnakangas<hlinnakangas@vmware.com>  wrote:
>> Regarding the change in pg_ctl:
>>
>>>          /*
>>> -        * Use two different kinds of promotion file so we can understand
>>> -        * the difference between smart and fast promotion.
>>> +        * For 9.3 onwards, use fast promotion as the default option.
>>> +        * Promotion with a full checkpoint is still possible by writing
>>> +        * a file called "promote", e.g.
>>> +        *       snprintf(promote_file, MAXPGPATH, "%s/promote", pg_data);
>>>           */
>>> -       if (shutdown_mode>= FAST_MODE)
>>> -               snprintf(promote_file, MAXPGPATH, "%s/fast_promote",
>>> pg_data);
>>> -       else
>>> -               snprintf(promote_file, MAXPGPATH, "%s/promote", pg_data);
>>> +       snprintf(promote_file, MAXPGPATH, "%s/fast_promote", pg_data);
>>
>>
>> Should there be a version check there? I guess we've never guaranteed a
>> newer pg_ctl to work with an older server version, but it seems likely that
>> someone would try to do that, especially with "pg_ctl promote". With the
>> above change, creating $DATADIR/fast_promote in a 9.2 server's data dir will
>> do nothing. I'd suggest that we keep the filename unchanged, "promote", and
>> only change the behavior in the server side, so that it performs fast
>> promotion. If you want to have a "slow" promote file, we can call that
>> "slow_promote" or "checkpoint_then_promote" or something.
>
> pg_ctl already checks versions, so I don't see the point.

The point is, if you do "pgsql93/bin/pg_ctl -D $92DATADIR promote", it 
will create fast_promote file and return success. But it won't actually 
promote the server. I think that's bad.

If pg_ctl already has a check against that, fine, but I don't think it 
does. Please make sure you test that before applying.

- Heikki