Re: [HACKERS] WAL logging problem in 9.4.3?

> On 13 Apr 2017, at 11:42, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
>
> At Thu, 13 Apr 2017 13:52:40 +0900, Michael Paquier <michael.paquier@gmail.com> wrote in
<CAB7nPqTRyica1d-zU+YckveFC876=Sc847etmk7TRgAS2pA9CA@mail.gmail.com>
>> On Tue, Apr 11, 2017 at 5:38 PM, Kyotaro HORIGUCHI
>> <horiguchi.kyotaro@lab.ntt.co.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.
>
> Thank you for the information. Removing unwanted test scripts
> from t/ directories was annoyance. This makes me happy.
>
>>>> - 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:
>
> Maybe this patch requires make clean since it extends the
> structure RelationData. (Perhaps I saw the same trouble.)
>
>> 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...
>
> I understand that the context of "backend process" means
> storage.c local. I don't mind the context on which the data is,
> but I found only there that can get rid of frequent hash
> searching. For pending deletions, just appending to a list is
> enough and costs almost nothing, on the other hand pendig syncs
> are required to be referenced, sometimes very frequently.
>
>> +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.
>
> Yeah.. It's in storage.c in the latest patch. (Sorry for the
> duplicate name). I think it is a kind of bond between smgr and
> relation.
>
>> 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.
>
> Agreed.
>
>> 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...
>
> My point is hash-search on every tuple insertion should be evaded
> even if it happens rearely. Once it was a bit apart from your
> original patch, but in the latest patch the significant part
> (pending-sync hash) is revived from the original one.

This patch has followed along since CF 2016-03, do we think we can reach a
conclusion in this CF?  It was marked as "Waiting on Author”, based on
developments since in this thread, I’ve changed it back to “Needs Review”
again.

cheers ./daniel