Horton

Re: [COMMITTERS] pgsql: Fix freezing of a dead HOT-updated tuple

Alvaro Herrera <alvherre@alvh.no-ip.org>

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From: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>, "Wood, Dan" <hexpert@amazon.com>
Date: 2017-10-01T13:31:01Z
Lists: pgsql-hackers 
Michael Paquier wrote:
> On Sun, Oct 1, 2017 at 10:25 AM, Peter Geoghegan <pg@bowt.ie> wrote:
> > On Thu, Sep 28, 2017 at 1:20 PM, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> >> Maybe what this means is that we need to do both Dan's initially
> >> proposed patch (or something related to it) apart from the fixes already
> >> pushed.  IOW we need to put back some of the "tupkeep" business ...
> >
> > I took the time to specifically check if that would fix the problem.
> > Unfortunately, it did not. We see exactly the same problem, or at
> > least amcheck/REINDEX produces exactly the same error. I checked both
> > Dan's original update_freeze.patch, and your revision that retained
> > some of the "tupkeep" stuff,
> > 0002-Don-t-freeze-recently-dead-HOT-tuples, which you posted on
> > September 6th.
> 
> I did not take the time to dig into that more than two hours, but my
> first feeling is that some race condition is going on with the heap
> pruning.

I'll look into this on Monday.  I found out yesterday that the
problematic case is when HTSV returns HEAPTUPLE_DEAD and the HOT tests
return true.  I haven't yet figured if it is one of those specifically,
but I suspect it is the IsHotUpdated case.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

  1. Backport addition of rs_old_rel to rewriteheap's state.

  2. Perform a lot more sanity checks when freezing tuples.

  3. Revert bogus fixes of HOT-freezing bug

  4. Fix traversal of half-frozen update chains

  5. Fix freezing of a dead HOT-updated tuple

  6. During index build, check and elog (not just Assert) for broken HOT chain.

  7. Fix WAL replay of locking an updated tuple

  8. Change the way we mark tuples as frozen.