Re: [HACKERS] WAL logging problem in 9.4.3?

Hello.

At Mon, 20 May 2019 15:54:30 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20190520(dot)155430(dot)215084510(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> > I suspect the design in the https://postgr.es/m/559FA0BA.3080808@iki.fi last
> > paragraph will be simpler, not more complex. In the implementation I'm
> > envisioning, smgrDoPendingDeletes() would change name, perhaps to
> > AtEOXact_Storage(). For every relfilenode it does not delete, it would ensure
> > durability by syncing (for large nodes) or by WAL-logging each page (for small
> > nodes). RelationNeedsWAL() would return false whenever the applicable
> > relfilenode appears in pendingDeletes. Access methods would remove their
> > smgrimmedsync() calls, but they would otherwise not change. Would anyone like
> > to try implementing that?
>
> Following this direction, the attached PoC works *at least for*
> the wal_optimization TAP tests, but doing pending flush not in
> smgr but in relcache. This is extending skip-wal feature to
> indexes. And makes the old 0002 patch on nbtree useless.

This is a tidier version of the patch.

- Passes regression tests including 018_wal_optimize.pl

- Move the substantial work to table/index AMs.

Each AM can decide whether to support WAL skip or not.
Currently heap and nbtree support it.

- The timing of sync is moved from AtEOXact to PreCommit. This is
because heap_sync() needs xact state = INPROGRESS.

- matview and cluster is broken, since swapping to new
relfilenode doesn't change rd_newRelfilenodeSubid. I'll address
that.

regards.

--
Kyotaro Horiguchi
NTT Open Source Software Center