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Commit78dcd02

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Fix potential memory leakage from HandleParallelMessages().
HandleParallelMessages leaked memory into the caller's context. Since it'scalled from ProcessInterrupts, there is basically zero certainty as to whatCurrentMemoryContext is, which means we could be leaking into long-livedcontexts. Over the processing of many worker messages that would grow tobe a problem. Things could be even worse than just a leak, if we happenedto service the interrupt while ErrorContext is current: elog.c thinks itcan reset that on its own whim, possibly yanking storage out from underHandleParallelMessages.Give HandleParallelMessages its own dedicated context instead, which we canreset during each call to ensure there's no accumulation of wasted memory.Discussion: <16610.1472222135@sss.pgh.pa.us>
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‎src/backend/access/transam/parallel.c

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Original file line numberDiff line numberDiff line change
@@ -702,6 +702,9 @@ void
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HandleParallelMessages(void)
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{
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dlist_iteriter;
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MemoryContextoldcontext;
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staticMemoryContexthpm_context=NULL;
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/*
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* This is invoked from ProcessInterrupts(), and since some of the
@@ -712,6 +715,23 @@ HandleParallelMessages(void)
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*/
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HOLD_INTERRUPTS();
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/*
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* Moreover, CurrentMemoryContext might be pointing almost anywhere. We
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* don't want to risk leaking data into long-lived contexts, so let's do
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* our work here in a private context that we can reset on each use.
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*/
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if (hpm_context==NULL)/* first time through? */
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hpm_context=AllocSetContextCreate(TopMemoryContext,
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"HandleParallelMessages context",
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ALLOCSET_DEFAULT_MINSIZE,
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ALLOCSET_DEFAULT_INITSIZE,
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ALLOCSET_DEFAULT_MAXSIZE);
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else
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MemoryContextReset(hpm_context);
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oldcontext=MemoryContextSwitchTo(hpm_context);
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/* OK to process messages. Reset the flag saying there are more to do. */
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ParallelMessagePending= false;
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dlist_foreach(iter,&pcxt_list)
@@ -758,6 +778,11 @@ HandleParallelMessages(void)
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}
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}
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MemoryContextSwitchTo(oldcontext);
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/* Might as well clear the context on our way out */
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MemoryContextReset(hpm_context);
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RESUME_INTERRUPTS();
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}
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