Don't invoke arbitrary code inside a possibly-aborted transaction.

robertmhaas · robertmhaas · commit 289992c462b5 · 2017-01-24T08:57:10.000-05:00
The code here previously tried to call the partitioning operator, but
really the right thing to do (and the safe thing to do) is use
datumIsEqual().

Amit Langote, but I expanded the comment and fixed a compiler warning.
diff --git a/src/backend/catalog/partition.c b/src/backend/catalog/partition.c
@@ -639,12 +639,20 @@ partition_bounds_equal(PartitionKey key,
 					continue;
 			}
 
-			/* Compare the actual values */
-			cmpval = DatumGetInt32(FunctionCall2Coll(&key->partsupfunc[j],
-													 key->partcollation[j],
-													 b1->datums[i][j],
-													 b2->datums[i][j]));
-			if (cmpval != 0)
+			/*
+			 * Compare the actual values. Note that it would be both incorrect
+			 * and unsafe to invoke the comparison operator derived from the
+			 * partitioning specification here.  It would be incorrect because
+			 * we want the relcache entry to be updated for ANY change to the
+			 * partition bounds, not just those that the partitioning operator
+			 * thinks are significant.  It would be unsafe because we might
+			 * reach this code in the context of an aborted transaction, and
+			 * an arbitrary partitioning operator might not be safe in that
+			 * context.  datumIsEqual() should be simple enough to be safe.
+			 */
+			if (!datumIsEqual(b1->datums[i][j], b2->datums[i][j],
+							  key->parttypbyval[j],
+							  key->parttyplen[j]))
 				return false;
 		}
 
diff --git a/src/backend/utils/adt/datum.c b/src/backend/utils/adt/datum.c
@@ -209,6 +209,10 @@ datumTransfer(Datum value, bool typByVal, int typLen)
  * of say the representation of zero in one's complement arithmetic).
  * Also, it will probably not give the answer you want if either
  * datum has been "toasted".
+ *
+ * Do not try to make this any smarter than it currently is with respect
+ * to "toasted" datums, because some of the callers could be working in the
+ * context of an aborted transaction.
  *-------------------------------------------------------------------------
  */
 bool
