Fix query-duration memory leak with GIN rescans.

The requiredEntries / additionalEntries arrays were not freed in
freeScanKeys() like other per-key stuff.

It's not obvious, but startScanKey() was only ever called after the keys
have been initialized with ginNewScanKey(). That's why it doesn't need to
worry about freeing existing arrays. The ginIsNewKey() test in gingetbitmap
was never true, because ginrescan free's the existing keys, and it's not OK
to call gingetbitmap twice in a row without calling ginrescan in between.
To make that clear, remove the unnecessary ginIsNewKey(). And just to be
extra sure that nothing funny happens if there is an existing key after all,
call freeScanKeys() to free it if it exists. This makes the code more
straightforward.

(I'm seeing other similar leaks in testing a query that rescans an GIN index
scan, but that's a different issue. This just fixes the obvious leak with
those two arrays.)

Backpatch to 9.4, where GIN fast scan was added.

Author: hlinnaka

src/backend/access/gin/ginget.c

@@ -560,6 +560,10 @@ startScan(IndexScanDesc scan)
 		}
 	}
 
+	/*
+	 * Now that we have the estimates for the entry frequencies, finish
+	 * initializing the scan keys.
+	 */
 	for (i = 0; i < so->nkeys; i++)
 		startScanKey(ginstate, so, so->keys + i);
 }
@@ -1763,23 +1767,23 @@ scanPendingInsert(IndexScanDesc scan, TIDBitmap *tbm, int64 *ntids)
 }
 
 
-#define GinIsNewKey(s)		( ((GinScanOpaque) scan->opaque)->keys == NULL )
 #define GinIsVoidRes(s)		( ((GinScanOpaque) scan->opaque)->isVoidRes )
 
 Datum
 gingetbitmap(PG_FUNCTION_ARGS)
 {
 	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
 	TIDBitmap  *tbm = (TIDBitmap *) PG_GETARG_POINTER(1);
+	GinScanOpaque so = (GinScanOpaque) scan->opaque;
 	int64		ntids;
 	ItemPointerData iptr;
 	bool		recheck;
 
 	/*
 	 * Set up the scan keys, and check for unsatisfiable query.
 	 */
-	if (GinIsNewKey(scan))
-		ginNewScanKey(scan);
+	ginFreeScanKeys(so); /* there should be no keys yet, but just to be sure */
+	ginNewScanKey(scan);
 
 	if (GinIsVoidRes(scan))
 		PG_RETURN_INT64(0);

src/backend/access/gin/ginscan.c

@@ -163,6 +163,10 @@ ginFillScanKey(GinScanOpaque so, OffsetNumber attnum,
 	key->curItemMatches = false;
 	key->recheckCurItem = false;
 	key->isFinished = false;
+	key->nrequired = 0;
+	key->nadditional = 0;
+	key->requiredEntries = NULL;
+	key->additionalEntries = NULL;
 
 	ginInitConsistentFunction(ginstate, key);
 
@@ -223,8 +227,8 @@ ginFillScanKey(GinScanOpaque so, OffsetNumber attnum,
 	}
 }
 
-static void
-freeScanKeys(GinScanOpaque so)
+void
+ginFreeScanKeys(GinScanOpaque so)
 {
 	uint32		i;
 
@@ -237,6 +241,10 @@ freeScanKeys(GinScanOpaque so)
 
 		pfree(key->scanEntry);
 		pfree(key->entryRes);
+		if (key->requiredEntries)
+			pfree(key->requiredEntries);
+		if (key->additionalEntries)
+			pfree(key->additionalEntries);
 	}
 
 	pfree(so->keys);
@@ -416,7 +424,7 @@ ginrescan(PG_FUNCTION_ARGS)
 	/* remaining arguments are ignored */
 	GinScanOpaque so = (GinScanOpaque) scan->opaque;
 
-	freeScanKeys(so);
+	ginFreeScanKeys(so);
 
 	if (scankey && scan->numberOfKeys > 0)
 	{
@@ -434,7 +442,7 @@ ginendscan(PG_FUNCTION_ARGS)
 	IndexScanDesc scan = (IndexScanDesc) PG_GETARG_POINTER(0);
 	GinScanOpaque so = (GinScanOpaque) scan->opaque;
 
-	freeScanKeys(so);
+	ginFreeScanKeys(so);
 
 	MemoryContextDelete(so->tempCtx);
 

src/include/access/gin_private.h

@@ -890,6 +890,7 @@ extern Datum ginrescan(PG_FUNCTION_ARGS);
 extern Datum ginmarkpos(PG_FUNCTION_ARGS);
 extern Datum ginrestrpos(PG_FUNCTION_ARGS);
 extern void ginNewScanKey(IndexScanDesc scan);
+extern void ginFreeScanKeys(GinScanOpaque so);
 
 /* ginget.c */
 extern Datum gingetbitmap(PG_FUNCTION_ARGS);