Horton

Re: [HACKERS] WAL logging problem in 9.4.3?

Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>

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From: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
To: robertmhaas@gmail.com
Cc: noah@leadboat.com, 9erthalion6@gmail.com, andrew.dunstan@2ndquadrant.com, hlinnaka@iki.fi, michael@paquier.xyz, pgsql-hackers@postgresql.org
Date: 2019-04-04T02:03:20Z
Lists: pgsql-hackers 
Thank you for looking this.

At Wed, 3 Apr 2019 10:16:02 -0400, Robert Haas <robertmhaas@gmail.com> wrote in <CA+TgmoYEST4xYaU10gM=XXeA-oxbFh=qSfy0X4PXDCWubcgj=g@mail.gmail.com>
> On Tue, Apr 2, 2019 at 6:54 AM Kyotaro HORIGUCHI
> <horiguchi.kyotaro@lab.ntt.co.jp> wrote:
> > > By using DELETE and INSERT records to implement an UPDATE, you lose the ctid
> > > chain and infomask bits that were present before crash recovery.  If that's
> > > okay in these circumstances, please write a comment explaining why.
> >
> > Sounds reasonable. Added a comment. (Honestly I completely forgot
> > about that.. Thanks!) (0006)
> 
> If you haven't already, I think you should set up a master and a
> standby and wal_consistency_checking=all and run tests of this feature
> on the master and see if anything breaks on the master or the standby.
> I'm not sure that emitting an insert or delete record is going to
> reproduce the exact same state on the standby that exists on the
> master.

All of this patch is for wal_level = minimal. Doesn't make
changes in other cases. Updates are always replicated as
XLOG_HEAP_(HOT_)UPDATE. Crash recovery cases involving log_insert
or log_update are exercised by the TAP test.

> + * Insert log record. Using delete or insert log loses HOT chain
> + * information but that happens only when newbuf is different from
> + * buffer, where HOT cannot happen.
> 
> "HOT chain information" seems pretty vague.

Thanks. Actually I was a bit uneasy with "information". Does the
following make sense?

> * Insert log record, using delete or insert instead of update log
> * when only one of the two buffers needs WAL-logging. If this were a
> * HOT-update, redoing the WAL record would result in a broken
> * hot-chain. However, that never happens because updates complete on
> * a single page always use log_update.

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. Add perl2host call missing from a new test file.

  2. Skip WAL for new relfilenodes, under wal_level=minimal.

  3. Revert "Skip WAL for new relfilenodes, under wal_level=minimal."

  4. Back-patch log_newpage_range().

  5. During heap rebuild, lock any TOAST index until end of transaction.

  6. In log_newpage_range(), heed forkNum and page_std arguments.

  7. Back-patch src/test/recovery and PostgresNode from 9.6 to 9.5.

  8. Reduce pg_ctl's reaction time when waiting for postmaster start/stop.

  9. Accelerate end-of-transaction dropping of relations

  10. Redesign the planner's handling of index-descent cost estimation.

  11. Make TRUNCATE do truncate-in-place when processing a relation that was created