Robert Haas wrote:
> On Fri, Apr 23, 2010 at 4:44 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>> Well, actually, now that I've looked at the patch I think it's starting
>> from a fundamentally wrong position anyway. Checkpoint records are a
>> completely wrong mechanism for transmitting this data to slaves, because
>> a checkpoint is emitted *after* we do something, not *before* we do it.
>> In particular it's ludicrous to be looking at shutdown checkpoints to
>> try to determine whether the subsequent WAL will meet the slave's
>> requirements. There's no connection at all between what the GUC state
>> was at shutdown and what it might be after starting again.
>>
>> A design that might work is
>> (1) store the active value of wal_mode in pg_control (but NOT as part of
>> the last-checkpoint-record image).
>> (2) invent a new WAL record type that is transmitted when we change
>> wal_mode.
>>
>> Then, slaves could check whether the master's wal_mode is high enough
>> by looking at pg_control when they start plus any wal_mode_change
>> records they come across.
>>
>> If we did this then we could get rid of those WAL record types that were
>> added to signify that information had been omitted from WAL at specific
>> times.
>
> <dons project manager hat>
>
> I notice that Heikki's patch doesn't include doing the above. Should
> we? If so, who's going to do it?
I'll give it a shot.
-- Heikki Linnakangas EnterpriseDB http://www.enterprisedb.com
