Re: WAL logging problem in 9.4.3?

Hello, thank you for looking this.

At Fri, 07 Apr 2017 20:38:35 -0400, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote in <27309(dot)1491611915(at)sss(dot)pgh(dot)pa(dot)us>
> Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > Interesting. I wonder if it's possible that a relcache invalidation
> > would cause these values to get lost for some reason, because that would
> > be dangerous.
>
> > I suppose the rationale is that this shouldn't happen because any
> > operation that does things this way must hold an exclusive lock on the
> > relation. But that doesn't guarantee that the relcache entry is
> > completely stable,
>
> It ABSOLUTELY is not safe. Relcache flushes can happen regardless of
> how strong a lock you hold.
>
> regards, tom lane

Ugh. Yes, relcache invalidation happens anytime and it resets the
added values. pg_stat_info deceived me that it can store
transient values. But I came up with another thought.

The reason I proposed it was I thought that hash_search for every
buffer is not good. Instead, like pg_stat_info, we can link the
pending-sync hash entry to Relation. This greately reduces the
frequency of hash-searching.

I'll post new patch in this way soon.

regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center