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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: Alvaro Herrera <alvherre@2ndquadrant.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: multivariate statistics v14
Date: Wed, 09 Mar 2016 18:21:42 +0100
Message-ID: <1457544102.24545.79.camel@2ndquadrant.com> (raw)
In-Reply-To: <CAMkU=1wDq9Gm+mg0YYY_JVw6kxYD6=n_FG-YPLrOFyWVnBhy9Q@mail.gmail.com>
References: <20160309122245.GA958049@alvherre.pgsql>
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Hi,

On Wed, 2016-03-09 at 08:45 -0800, Jeff Janes wrote:
> On Wed, Mar 9, 2016 at 7:02 AM, Tomas Vondra
> <tomas.vondra@2ndquadrant.com> wrote:
> > Hi,
> >
> > thanks for the feedback. Attached is v14 of the patch series, fixing
> > most of the points you've raised.
> 
> 
> Hi Tomas,
> 
> Applied to aa09cd242fa7e3a694a31f, I still get the seg faults in make
> check if I configure without --enable-cassert.

Ah, after disabling asserts I can reproduce it too. And the reason why
it fails is quite simple - clauselist_selectivity modifies the original
list of clauses, which then confuses cost_qual_eval.

Can you try if the attached patch fixes the issue? I'll need to rework a
bit more of the code, but let's see if this fixes the issue on your
machine too.

> With --enable-cassert, it passes the regression test.

I wonder how can it work with casserts and fail without them. That's
kinda exactly the opposite to what I'd expect ...

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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Attachments:

  [text/x-patch] mvstats-segfault-fix.patch (642B, ../1457544102.24545.79.camel@2ndquadrant.com/2-mvstats-segfault-fix.patch)
  download | inline diff:
diff --git a/src/backend/optimizer/path/clausesel.c b/src/backend/optimizer/path/clausesel.c
index 2540da9..ddfdc3b 100644
--- a/src/backend/optimizer/path/clausesel.c
+++ b/src/backend/optimizer/path/clausesel.c
@@ -279,6 +279,10 @@ clauselist_selectivity(PlannerInfo *root,
 		List *solution = choose_mv_statistics(root, relid, stats,
 											  clauses, conditions);
 
+		/* FIXME we must not scribble over the original list */
+		if (solution)
+			clauses = list_copy(clauses);
+
 		/*
 		 * We have a good solution, which is merely a list of statistics that
 		 * we need to apply. We'll apply the statistics one by one (in the order

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  To: pgsql-hackers@postgresql.org
  Cc: tomas.vondra@2ndquadrant.com, jeff.janes@gmail.com, alvherre@2ndquadrant.com
  Subject: Re: multivariate statistics v14
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