On 13-03-2015 PM 05:32, Amit Langote wrote:
> On 12-03-2015 PM 11:46, Amit Kapila wrote:
>> [parallel_seqscan_v10.patch]
>
> There may be a bug in TupleQueueFunnelNext().
>
> 1) I observed a hang with stack looking like:
>
> #0 0x00000039696df098 in poll () from /lib64/libc.so.6
> #1 0x00000000006f1c6a in WaitLatchOrSocket (latch=0x7f29dc3c73b4,
> wakeEvents=1, sock=-1, timeout=0) at pg_latch.c:333
> #2 0x00000000006f1aca in WaitLatch (latch=0x7f29dc3c73b4, wakeEvents=1,
> timeout=0) at pg_latch.c:197
> #3 0x000000000065088b in TupleQueueFunnelNext (funnel=0x17b4a20, nowait=0
> '\000', done=0x17ad481 "") at tqueue.c:269
> #4 0x0000000000636cab in funnel_getnext (funnelstate=0x17ad3d0) at
> nodeFunnel.c:347
> ...
> <snip>
>
> 2) In some cases, there can be a segmentation fault with stack looking like:
>
> #0 0x000000396968990a in memcpy () from /lib64/libc.so.6
> #1 0x00000000006507e7 in TupleQueueFunnelNext (funnel=0x263c800, nowait=0
> '\000', done=0x2633461 "") at tqueue.c:233
> #2 0x0000000000636cab in funnel_getnext (funnelstate=0x26333b0) at
> nodeFunnel.c:347
> #3 0x0000000000636901 in ExecFunnel (node=0x26333b0) at nodeFunnel.c:179
> ...
> <snip>
>
> I could get rid of (1) and (2) with the attached fix.
Hit send too soon!
By the way, the bug seems to be exposed only with a certain pattern/sequence
of workers being detached (perhaps in immediate successive) whereby the
funnel->nextqueue remains incorrectly set.
The patch attached this time.
By the way, when I have asserts enabled, I hit this compilation error:
createplan.c: In function ‘create_partialseqscan_plan’:
createplan.c:1180: error: ‘Path’ has no member named ‘path’
I see following line there:
Assert(best_path->path.parent->rtekind == RTE_RELATION);
Thanks,
Amit
diff --git a/src/backend/executor/tqueue.c b/src/backend/executor/tqueue.c
index ee4e03e..8a6c6f3 100644
--- a/src/backend/executor/tqueue.c
+++ b/src/backend/executor/tqueue.c
@@ -234,6 +234,8 @@ TupleQueueFunnelNext(TupleQueueFunnel *funnel, bool nowait, bool *done)
&funnel->queue[funnel->nextqueue + 1],
sizeof(shm_mq_handle *)
* (funnel->nqueues - funnel->nextqueue));
+
+ funnel->nextqueue = (funnel->nextqueue + 1) % funnel->nqueues;
if (funnel->nextqueue < waitpos)
--waitpos;
}
@@ -260,7 +262,7 @@ TupleQueueFunnelNext(TupleQueueFunnel *funnel, bool nowait, bool *done)
* and return NULL (if we're in non-blocking mode) or wait for the
* process latch to be set (otherwise).
*/
- if (funnel->nextqueue == waitpos)
+ if (result != SHM_MQ_DETACHED && funnel->nextqueue == waitpos)
{
if (nowait)
return NULL;
--
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