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From: Tom Lane <[email protected]>
To: David Rowley <[email protected]>
Cc: [email protected]
Cc: [email protected]
Subject: Re: BUG #19438: segfault with temp_file_limit inside cursor
Date: Mon, 30 Mar 2026 12:29:20 -0400
Message-ID: <[email protected]> (raw)
In-Reply-To: <[email protected]>
References: <[email protected]>
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I wrote:
> Works for me.  I'm done for the day but will make it so tomorrow.

Pushed that, though in the event I wrote a rather longer apologia
for why we use ERROR in one complaint and WARNING in the other.

Getting back to the original bug ... I went through tuplestore.c
and found two other places where foreseeable failures in subroutines
could leave the tuplestore in an inconsistent state.  I think we
need to fix them all, per the attached draft against HEAD.  The
back branches might have more/different bugs, didn't look yet.

			regards, tom lane



Attachments:

  [text/x-diff] v2-fix-tuplestore-inconsistency-after-error.patch (1.9K, 2-v2-fix-tuplestore-inconsistency-after-error.patch)
  download | inline diff:
diff --git a/src/backend/utils/sort/tuplestore.c b/src/backend/utils/sort/tuplestore.c
index caad7cad0b4..f9e2d95186a 100644
--- a/src/backend/utils/sort/tuplestore.c
+++ b/src/backend/utils/sort/tuplestore.c
@@ -708,10 +708,10 @@ grow_memtuples(Tuplestorestate *state)
 
 	/* OK, do it */
 	FREEMEM(state, GetMemoryChunkSpace(state->memtuples));
-	state->memtupsize = newmemtupsize;
 	state->memtuples = (void **)
 		repalloc_huge(state->memtuples,
-					  state->memtupsize * sizeof(void *));
+					  newmemtupsize * sizeof(void *));
+	state->memtupsize = newmemtupsize;
 	USEMEM(state, GetMemoryChunkSpace(state->memtuples));
 	if (LACKMEM(state))
 		elog(ERROR, "unexpected out-of-memory situation in tuplestore");
@@ -1306,7 +1306,19 @@ dumptuples(Tuplestorestate *state)
 		if (i >= state->memtupcount)
 			break;
 		WRITETUP(state, state->memtuples[i]);
+
+		/*
+		 * Increase memtupdeleted to track the fact that we just deleted that
+		 * tuple.  Think not to remove this on the grounds that we'll reset
+		 * memtupdeleted to zero below.  We might not reach that if some later
+		 * WRITETUP fails (e.g. due to overrunning temp_file_limit).  If so,
+		 * we'd error out leaving an effectively-corrupt tuplestore, which
+		 * would be quite bad if it's a persistent data structure such as a
+		 * Portal's holdStore.
+		 */
+		state->memtupdeleted++;
 	}
+	/* Now we can reset memtupdeleted along with memtupcount */
 	state->memtupdeleted = 0;
 	state->memtupcount = 0;
 }
@@ -1496,8 +1508,10 @@ tuplestore_trim(Tuplestorestate *state)
 		FREEMEM(state, GetMemoryChunkSpace(state->memtuples[i]));
 		pfree(state->memtuples[i]);
 		state->memtuples[i] = NULL;
+		/* As in dumptuples(), increment memtupdeleted synchronously */
+		state->memtupdeleted++;
 	}
-	state->memtupdeleted = nremove;
+	Assert(state->memtupdeleted == nremove);
 
 	/* mark tuplestore as truncated (used for Assert crosschecks only) */
 	state->truncated = true;

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