Re: WAL logging problem in 9.4.3?

On Tue, Apr 11, 2017 at 5:38 PM, Kyotaro HORIGUCHI
<horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote:
> Sorry, what I have just sent was broken.

You can use PROVE_TESTS when running make check to select a subset of
tests you want to run. I use that all the time when working on patches
dedicated to certain code paths.

>> - Relation has new members no_pending_sync and pending_sync that
>> works as instant cache of an entry in pendingSync hash.
>> - Commit-time synchronizing is restored as Michael's patch.
>> - If relfilenode is replaced, pending_sync for the old node is
>> removed. Anyway this is ignored on abort and meaningless on
>> commit.
>> - TAP test is renamed to 012 since some new files have been added.
>>
>> Accessing pending sync hash occurred on every calling of
>> HeapNeedsWAL() (per insertion/update/freeze of a tuple) if any of
>> accessing relations has pending sync. Almost of them are
>> eliminated as the result.

Did you actually test this patch? One of the logs added makes the
tests a long time to run:
2017-04-13 12:11:27.065 JST [85441] t/102_vacuumdb_stages.pl
STATEMENT: ANALYZE;
2017-04-13 12:12:25.766 JST [85492] LOG: BufferNeedsWAL: pendingSyncs
= 0x0, no_pending_sync = 0

- lsn = XLogInsert(RM_SMGR_ID,
- XLOG_SMGR_TRUNCATE | XLR_SPECIAL_REL_UPDATE);
+ rel->no_pending_sync= false;
+ rel->pending_sync = pending;
+ }
It seems to me that those flags and the pending_sync data should be
kept in the context of backend process and not be part of the Relation
data...

+void
+RecordPendingSync(Relation rel)
I don't think that I agree that this should be part of relcache.c. The
syncs are tracked should be tracked out of the relation context.

Seeing how invasive this change is, I would also advocate for this
patch as only being a HEAD-only change, not many people are
complaining about this optimization of TRUNCATE missing when wal_level
= minimal, and this needs a very careful review.

Should I code something? Or Horiguchi-san, would you take care of it?
The previous crash I saw has been taken care of, but it's been really
some time since I looked at this patch...
--
Michael