Horton

Re: [HACKERS] WAL logging problem in 9.4.3?

Noah Misch <noah@leadboat.com>

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From: Noah Misch <noah@leadboat.com>
To: Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Cc: 9erthalion6@gmail.com, andrew.dunstan@2ndquadrant.com, hlinnaka@iki.fi, robertmhaas@gmail.com, michael@paquier.xyz, pgsql-hackers@postgresql.org
Date: 2019-03-21T05:48:35Z
Lists: pgsql-hackers 
On Wed, Mar 20, 2019 at 05:17:54PM +0900, Kyotaro HORIGUCHI wrote:
> At Sun, 10 Mar 2019 19:27:08 -0700, Noah Misch <noah@leadboat.com> wrote in <20190311022708.GA2189728@rfd.leadboat.com>
> > On Mon, Mar 04, 2019 at 12:24:48PM +0900, Kyotaro HORIGUCHI wrote:
> > > +/*
> > > + * Sync to disk any relations that we skipped WAL-logging for earlier.
> > > + */
> > > +void
> > > +smgrDoPendingSyncs(bool isCommit)
> > > +{
> > > +	if (!pendingSyncs)
> > > +		return;
> > > +
> > > +	if (isCommit)
> > > +	{
> > > +		HASH_SEQ_STATUS status;
> > > +		PendingRelSync *pending;
> > > +
> > > +		hash_seq_init(&status, pendingSyncs);
> > > +
> > > +		while ((pending = hash_seq_search(&status)) != NULL)
> > > +		{
> > > +			if (pending->sync_above != InvalidBlockNumber)
> > 
> > I'm mildly unhappy that pendingSyncs entries with "pending->sync_above ==
> > InvalidBlockNumber" are not sync requests at all.  Those just record the fact
> > of a RelationTruncate() happening.  If you can think of a way to improve that,
> > please do so.  If not, it's okay.
> 
> After a truncation, required WAL records are emitted for the
> truncated pages, so no need to sync. Does this make sense for
> you? (Maybe commit is needed there)

Yes, the behavior makes sense.  I wasn't saying the quoted code had the wrong
behavior.  I was saying that the data structure called "pendingSyncs" is
actually "pending syncs and past truncates".  It's not ideal that the variable
name differs from the variable purpose in this way.  However, it's okay if you
don't find a way to improve that.

> I don't have enough time for now so the new version will be
> posted early next week.

I'll wait for that version.

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