Re: [9.4] Make full_page_writes only settable on server start?

On 2013-09-04 09:23:20 -0700, Jeff Davis wrote:
> On Wed, 2013-09-04 at 11:32 -0400, Tom Lane wrote:
> > Jeff Davis <pgsql@j-davis.com> writes:
> > > I think code complexity matters quite a lot. If we can eliminate some
> > > complex code in a complex area, and all we give up is a feature with
> > > essentially no use case, that sounds like we're moving in the right
> > > direction to me.
> > 
> > Isn't this whole discussion academic in view of Andres' point?
> 
> Maybe "complex code" was an overstatement. We'd be able to eliminate the
> XLOG_FPW_CHANGE, UpdateFullPageWrites(), and one of the members of
> XLogCtlInsert; and make xlog.c slightly shorter in the process.

That path is also executed during a normal restart and during
promotion. Check the invocation of UpdateFullPageWrites() in
StartupXLOG(). Note that a standby needs to be able to follow a
primaries full_page_writes setting during a promotion.

Greetings,

Andres Freund

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