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Don't be so trusting that shm_toc_lookup() will always succeed.

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Given the possibility of race conditions and so on, it seems entirely
unsafe to just assume that shm_toc_lookup() always finds the key it's
looking for --- but that was exactly what all but one call site were
doing.  To fix, add a "bool noError" argument, similarly to what we
have in many other functions, and throw an error on an unexpected
lookup failure.  Remove now-redundant Asserts that a rather random
subset of call sites had.

I doubt this will throw any light on buildfarm member lorikeet's
recent failures, because if an unnoticed lookup failure were involved,
you'd kind of expect a null-pointer-dereference crash rather than the
observed symptom.  But you never know ... and this is better coding
practice even if it never catches anything.

Discussion: https://postgr.es/m/9697.1496675981@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2017-06-05 12:05:42 -04:00
parent af51fea039
commit d466335064
11 changed files with 39 additions and 38 deletions
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16
src/backend/executor/execParallel.c
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@ -341,7 +341,7 @@ ExecParallelSetupTupleQueues(ParallelContext *pcxt, bool reinitialize)
mul_size(PARALLEL_TUPLE_QUEUE_SIZE,
pcxt->nworkers));
else
tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE);
tqueuespace = shm_toc_lookup(pcxt->toc, PARALLEL_KEY_TUPLE_QUEUE, false);
/* Create the queues, and become the receiver for each. */
for (i = 0; i < pcxt->nworkers; ++i)
@ -684,7 +684,7 @@ ExecParallelGetReceiver(dsm_segment *seg, shm_toc *toc)
char *mqspace;
shm_mq *mq;
mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE);
mqspace = shm_toc_lookup(toc, PARALLEL_KEY_TUPLE_QUEUE, false);
mqspace += ParallelWorkerNumber * PARALLEL_TUPLE_QUEUE_SIZE;
mq = (shm_mq *) mqspace;
shm_mq_set_sender(mq, MyProc);
@ -705,14 +705,14 @@ ExecParallelGetQueryDesc(shm_toc *toc, DestReceiver *receiver,
char *queryString;
/* Get the query string from shared memory */
queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT);
queryString = shm_toc_lookup(toc, PARALLEL_KEY_QUERY_TEXT, false);
/* Reconstruct leader-supplied PlannedStmt. */
pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT);
pstmtspace = shm_toc_lookup(toc, PARALLEL_KEY_PLANNEDSTMT, false);
pstmt = (PlannedStmt *) stringToNode(pstmtspace);
/* Reconstruct ParamListInfo. */
paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMS);
paramspace = shm_toc_lookup(toc, PARALLEL_KEY_PARAMS, false);
paramLI = RestoreParamList(&paramspace);
/*
@ -843,7 +843,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
/* Set up DestReceiver, SharedExecutorInstrumentation, and QueryDesc. */
receiver = ExecParallelGetReceiver(seg, toc);
instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION);
instrumentation = shm_toc_lookup(toc, PARALLEL_KEY_INSTRUMENTATION, true);
if (instrumentation != NULL)
instrument_options = instrumentation->instrument_options;
queryDesc = ExecParallelGetQueryDesc(toc, receiver, instrument_options);
@ -858,7 +858,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
InstrStartParallelQuery();
/* Attach to the dynamic shared memory area. */
area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA);
area_space = shm_toc_lookup(toc, PARALLEL_KEY_DSA, false);
area = dsa_attach_in_place(area_space, seg);
/* Start up the executor */
@ -875,7 +875,7 @@ ParallelQueryMain(dsm_segment *seg, shm_toc *toc)
ExecutorFinish(queryDesc);
/* Report buffer usage during parallel execution. */
buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE);
buffer_usage = shm_toc_lookup(toc, PARALLEL_KEY_BUFFER_USAGE, false);
InstrEndParallelQuery(&buffer_usage[ParallelWorkerNumber]);
/* Report instrumentation data if any instrumentation options are set. */