Re: Logging WAL when updating hintbit

On Tue, Dec 3, 2013 at 1:08 AM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Mon, Dec 2, 2013 at 12:54 AM, Michael Paquier
>> Considering that, it would make more sense to have this option
>> settable with initdb only and not changeable after initialization, in
>> the same fashion as checksums. Having a GUC that can be used to check
>> if this option is set or not using a SQL command could be an
>> additional patch on top of the core feature.
>
> Forcing it to be done only an initdb-time is excessive.  I think you
> can just make it PGC_POSTMASTER and have it participate in the
> XLOG_PARAMETER_CHANGE mechanism.  pg_rewind can check that it's set in
> the control file before agreeing to rewind.
Yes, this is only a matter of adding a couple of lines of code.

> As long as it was set at
> the time the master last entered read-write mode (which is what the
> XLOG_PARAMETER_CHANGE stuff does) you should be fine, unless of course
> I haven't had enough caffeine this morning, which is certainly
> possible.
Indeed, I forgot this code path. Completing XLogReportParameters for
saving the state and xlog_redo for replay would be enough.
-- 
Michael