Horton

Re: WAL logging problem in 9.4.3?

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Andres Freund <andres@anarazel.de>
Cc: Fujii Masao <masao.fujii@gmail.com>, Martijn van Oosterhout <kleptog@svana.org>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2015-07-03T22:38:37Z
Lists: pgsql-hackers 
Andres Freund <andres@anarazel.de> writes:
> On 2015-07-03 19:26:05 +0200, Andres Freund wrote:
>> commit cab9a0656c36739f59277b34fea8ab9438395869
>> Author: Tom Lane <tgl@sss.pgh.pa.us>
>> Date:   Sun Aug 23 19:23:41 2009 +0000
>> 
>> Make TRUNCATE do truncate-in-place when processing a relation that was created
>> or previously truncated in the current (sub)transaction.  This is safe since
>> if the (sub)transaction later rolls back, we'd just discard the rel's current
>> physical file anyway.  This avoids unreasonable growth in the number of
>> transient files when a relation is repeatedly truncated.  Per a performance
>> gripe a couple weeks ago from Todd Cook.
>> 
>> to me the reasoning here looks flawed.

> It looks to me we need to re-neg on this a bit. I think we can still be
> more efficient than the general codepath: We can drop the old
> relfilenode immediately. But pg_class.relfilenode has to differ from the
> old after the truncation.

Why exactly?  The first truncation in the (sub)xact would have assigned a
new relfilenode, why do we need another one?  The file in question will
go away on crash/rollback in any case, and no other transaction can see
it yet.

I'm prepared to believe that some bit of logic is doing the wrong thing in
this state, but I do not agree that truncate-in-place is unworkable.

			regards, tom lane

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