Re: Problem while setting the fpw with SIGHUP

On Wed, Apr 11, 2018 at 02:09:48PM +0300, Heikki Linnakangas wrote:
> I think the new behavior where the GUC only takes effect at next checkpoint
> is OK. It seems quite intuitive.
>
> > [rebased patch version]
>
> Looks good at a quick glance. Assuming no objections from others, I'll take
> a closer look and commit tomorrow. Thanks!

Sorry for not following up closely this thread lately.

+ /*
+ * If full_page_writes has been turned off, issue XLOG_FPW_CHANGE before
+ * the flag actually takes effect. No lock is required since checkpointer
+ * is the only updator of shared fullPageWrites after recovery is
+ * finished. Both shared and local fullPageWrites do not change before the
+ * next reading below.
+ */
+ if (Insert->fullPageWrites && !fullPageWrites)
+ {
+ XLogBeginInsert();
+ XLogRegisterData((char *) (&fullPageWrites), sizeof(bool));
+ XLogInsert(RM_XLOG_ID, XLOG_FPW_CHANGE);
+ }

This is not actually true. If a fallback_promote is used, then
CreateCheckPoint() is called by the startup process which is in charge
of issuing the end-of-recovery checkpoint, and not the checkpointer. So
I still fail to see how a no-lock approach is fine except if we remove
fallback_promote?
--
Michael