Horton

Re: 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: tgl@sss.pgh.pa.us
Cc: alvherre@2ndquadrant.com, michael.paquier@gmail.com, david@pgmasters.net, hlinnaka@iki.fi, simon@2ndquadrant.com, andres@anarazel.de, masao.fujii@gmail.com, kleptog@svana.org, pgsql-hackers@postgresql.org
Date: 2017-04-11T00:56:06Z
Lists: pgsql-hackers 
Hello, thank you for looking this.

At Fri, 07 Apr 2017 20:38:35 -0400, Tom Lane <tgl@sss.pgh.pa.us> wrote in <27309.1491611915@sss.pgh.pa.us>
> Alvaro Herrera <alvherre@2ndquadrant.com> writes:
> > Interesting.  I wonder if it's possible that a relcache invalidation
> > would cause these values to get lost for some reason, because that would
> > be dangerous.
> 
> > I suppose the rationale is that this shouldn't happen because any
> > operation that does things this way must hold an exclusive lock on the
> > relation.  But that doesn't guarantee that the relcache entry is
> > completely stable,
> 
> It ABSOLUTELY is not safe.  Relcache flushes can happen regardless of
> how strong a lock you hold.
> 
> 			regards, tom lane

Ugh. Yes, relcache invalidation happens anytime and it resets the
added values. pg_stat_info deceived me that it can store
transient values. But I  came up with another thought.

The reason I proposed it was I thought that hash_search for every
buffer is not good. Instead, like pg_stat_info, we can link the
pending-sync hash entry to Relation. This greately reduces the
frequency of hash-searching.

I'll post new patch in this way soon.

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