From: Tom Lane <tgl@sss.pgh.pa.us>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Ondřej Jirman <ienieghapheoghaiwida@xff.cz>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16129: Segfault in tts_virtual_materialize in logical replication worker
Date: Thu, 21 Nov 2019 18:56:47 -0500
Message-ID: <14166.1574380607@sss.pgh.pa.us> (raw)
In-Reply-To: <20191121234701.2wtyc77zd5ux3myf@development>
References: <20191121150716.szxqukxrtpjpckm3@core.my.home>
<20191121152732.hu6y4wzw7nkxpsvk@development>
<20191121155707.pqkgjphh65o5fapz@core.my.home>
<20191121161502.xfiy65i3cm6adscr@core.my.home>
<20191121165752.dffge6bh756xlfdg@development>
<20191121173555.midj6vp4dmiiqs24@core.my.home>
<20191121185844.6qsqhwzzuhu3fpsg@core.my.home>
<20191121214115.3tgefmvkmrzaim74@development>
<20191121220854.ebdzjtloel56sfwu@development>
<13122.1574375845@sss.pgh.pa.us>
<20191121234701.2wtyc77zd5ux3myf@development>
Tomas Vondra <tomas.vondra@2ndquadrant.com> writes:
> On Thu, Nov 21, 2019 at 05:37:25PM -0500, Tom Lane wrote:
> I don't think that's quite true. After the ExecCopySlot call, the
> pass-by-ref Datums in remoteslot will point to a tuple attached to
> localslot. But it does not pass the tuple 'ownership' to the remoteslot,
> i.e. the flag TTS_FLAG_SHOULDFREE won't be set, i.e. the tuple won't be
> freed.
Nope:
static void
tts_heap_copyslot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
HeapTuple tuple;
MemoryContext oldcontext;
oldcontext = MemoryContextSwitchTo(dstslot->tts_mcxt);
tuple = ExecCopySlotHeapTuple(srcslot);
MemoryContextSwitchTo(oldcontext);
ExecStoreHeapTuple(tuple, dstslot, true);
}
"remoteslot" will contain its very own copy of the data, which
is then summarily freed by ExecClearSlot.
>> I imagine the only reason this code has gotten past the valgrind
>> animals is that we're not testing cases where non-replaced columns
>> in the subscriber table are of pass-by-ref types.
> I haven't checked, but I'd imagine we actually do such tests. I've
> however tried to reproduce this, unsuccessfully.
I did check, and we don't. See patch.
It's possible that the OP is seeing some different problem,
but I can definitely demonstrate that there is a problem
that this change fixes.
regards, tom lane
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To: pgsql-bugs@postgresql.org
Cc: tgl@sss.pgh.pa.us, tomas.vondra@2ndquadrant.com, ienieghapheoghaiwida@xff.cz, pgsql-bugs@lists.postgresql.org
Subject: Re: BUG #16129: Segfault in tts_virtual_materialize in logical replication worker
In-Reply-To: <14166.1574380607@sss.pgh.pa.us>
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