Re: Valgrind failures caused by multivariate stats patch

On 03/25/2017 10:10 PM, Andres Freund wrote:
...
> ==2486== Uninitialised byte(s) found during client check request
> ==2486== at 0x1C4857: printtup (printtup.c:347)
> ==2486== by 0x401FD5: ExecutePlan (execMain.c:1681)
> ==2486== by 0x3FFDED: standard_ExecutorRun (execMain.c:355)
> ==2486== by 0x3FFC07: ExecutorRun (execMain.c:298)
> ==2486== by 0x5C40BD: PortalRunSelect (pquery.c:928)
> ==2486== by 0x5C3D50: PortalRun (pquery.c:769)
> ==2486== by 0x5BDC1A: exec_simple_query (postgres.c:1101)
> ==2486== by 0x5C203F: PostgresMain (postgres.c:4071)
> ==2486== by 0x525138: BackendRun (postmaster.c:4317)
> ==2486== by 0x524848: BackendStartup (postmaster.c:3989)
> ==2486== by 0x520C4A: ServerLoop (postmaster.c:1729)
> ==2486== by 0x5201D9: PostmasterMain (postmaster.c:1337)
> ==2486== by 0x45DFA6: main (main.c:228)
> ==2486== Address 0x3e8c50f5 is in a rw- anonymous segment
> ==2486== Uninitialised value was created by a heap allocation
> ==2486== at 0x76212F: palloc (mcxt.c:872)
> ==2486== by 0x578814: statext_ndistinct_build (mvdistinct.c:80)
> ==2486== by 0x577CCE: BuildRelationExtStatistics (extended_stats.c:94)
> ==2486== by 0x3546B6: do_analyze_rel (analyze.c:577)
> ==2486== by 0x353B76: analyze_rel (analyze.c:271)
> ==2486== by 0x3E7B89: vacuum (vacuum.c:321)
> ==2486== by 0x3E7755: ExecVacuum (vacuum.c:122)
> ==2486== by 0x5C5F1C: standard_ProcessUtility (utility.c:670)
> ==2486== by 0x5C5724: ProcessUtility (utility.c:353)
> ==2486== by 0x5C46CA: PortalRunUtility (pquery.c:1174)
> ==2486== by 0x5C48D0: PortalRunMulti (pquery.c:1317)
> ==2486== by 0x5C3E1A: PortalRun (pquery.c:795)
> ==2486== by 0x5BDC1A: exec_simple_query (postgres.c:1101)
> ==2486== by 0x5C203F: PostgresMain (postgres.c:4071)
> ==2486== by 0x525138: BackendRun (postmaster.c:4317)
> ==2486== by 0x524848: BackendStartup (postmaster.c:3989)
> ==2486== by 0x520C4A: ServerLoop (postmaster.c:1729)
> ==2486== by 0x5201D9: PostmasterMain (postmaster.c:1337)
> ==2486== by 0x45DFA6: main (main.c:228)

Hmmm, so I have a theory about what's going on, but no matter what I do
I can't trigger these valgrind failures. What switches are you using to
start valgrind? I'm using this:

valgrind --leak-check=no --undef-value-errors=yes \
--expensive-definedness-checks=yes --track-origins=yes \
--read-var-info=yes --gen-suppressions=all \
--suppressions=src/tools/valgrind.supp --time-stamp=yes \
--log-file=$HOME/pg-valgrind/%p.log --trace-children=yes \
postgres --log_line_prefix="%m %p " --log_statement=all \
--shared_buffers=64MB -D /home/user/tmp/data-valgrind 2>&1

FWIW I think the issue is that statext_ndistinct_build does palloc() and
then uses offsetof() to copy data into the chunk, which might result in
a few bytes skipped due to alignment/padding. But as I can't reproduce
the valgrind failure, it's hard to say.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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