Use a separate memory context for GIN scan keys.

It was getting tedious to track and release all the different things that
form a scan key. We were leaking at least the queryCategories array, and
possibly more, on a rescan. That was visible if a GIN index was used in a
nested loop join. This also protects from leaks in extractQuery method.

No backpatching, given the lack of complaints from the field. Maybe later,
after this has received more field testing.

src/backend/access/gin/ginget.c

@@ -497,7 +497,7 @@ startScanKey(GinState *ginstate, GinScanOpaque so, GinScanKey key)
 		}
 		/* i is now the last required entry. */
 
-		MemoryContextSwitchTo(oldCtx);
+		MemoryContextSwitchTo(so->keyCtx);
 
 		key->nrequired = i + 1;
 		key->nadditional = key->nentries - key->nrequired;
@@ -515,11 +515,14 @@ startScanKey(GinState *ginstate, GinScanOpaque so, GinScanKey key)
 	}
 	else
 	{
+		MemoryContextSwitchTo(so->keyCtx);
+
 		key->nrequired = 1;
 		key->nadditional = 0;
 		key->requiredEntries = palloc(1 * sizeof(GinScanEntry));
 		key->requiredEntries[0] = key->scanEntry[0];
 	}
+	MemoryContextSwitchTo(oldCtx);
 }
 
 static void

src/backend/access/gin/ginscan.c

@@ -44,6 +44,11 @@ ginbeginscan(PG_FUNCTION_ARGS)
 										ALLOCSET_DEFAULT_MINSIZE,
 										ALLOCSET_DEFAULT_INITSIZE,
 										ALLOCSET_DEFAULT_MAXSIZE);
+	so->keyCtx = AllocSetContextCreate(CurrentMemoryContext,
+									   "Gin scan key context",
+									   ALLOCSET_DEFAULT_MINSIZE,
+									   ALLOCSET_DEFAULT_INITSIZE,
+									   ALLOCSET_DEFAULT_MAXSIZE);
 	initGinState(&so->ginstate, scan->indexRelation);
 
 	scan->opaque = so;
@@ -227,6 +232,9 @@ ginFillScanKey(GinScanOpaque so, OffsetNumber attnum,
 	}
 }
 
+/*
+ * Release current scan keys, if any.
+ */
 void
 ginFreeScanKeys(GinScanOpaque so)
 {
@@ -235,38 +243,22 @@ ginFreeScanKeys(GinScanOpaque so)
 	if (so->keys == NULL)
 		return;
 
-	for (i = 0; i < so->nkeys; i++)
-	{
-		GinScanKey	key = so->keys + i;
-
-		pfree(key->scanEntry);
-		pfree(key->entryRes);
-		if (key->requiredEntries)
-			pfree(key->requiredEntries);
-		if (key->additionalEntries)
-			pfree(key->additionalEntries);
-	}
-
-	pfree(so->keys);
-	so->keys = NULL;
-	so->nkeys = 0;
-
 	for (i = 0; i < so->totalentries; i++)
 	{
 		GinScanEntry entry = so->entries[i];
 
 		if (entry->buffer != InvalidBuffer)
 			ReleaseBuffer(entry->buffer);
-		if (entry->list)
-			pfree(entry->list);
 		if (entry->matchIterator)
 			tbm_end_iterate(entry->matchIterator);
 		if (entry->matchBitmap)
 			tbm_free(entry->matchBitmap);
-		pfree(entry);
 	}
 
-	pfree(so->entries);
+	MemoryContextResetAndDeleteChildren(so->keyCtx);
+
+	so->keys = NULL;
+	so->nkeys = 0;
 	so->entries = NULL;
 	so->totalentries = 0;
 }
@@ -278,6 +270,14 @@ ginNewScanKey(IndexScanDesc scan)
 	GinScanOpaque so = (GinScanOpaque) scan->opaque;
 	int			i;
 	bool		hasNullQuery = false;
+	MemoryContext oldCtx;
+
+	/*
+	 * Allocate all the scan key information in the key context. (If
+	 * extractQuery leaks anything there, it won't be reset until the end of
+	 * scan or rescan, but that's OK.)
+	 */
+	oldCtx = MemoryContextSwitchTo(so->keyCtx);
 
 	/* if no scan keys provided, allocate extra EVERYTHING GinScanKey */
 	so->keys = (GinScanKey)
@@ -412,6 +412,8 @@ ginNewScanKey(IndexScanDesc scan)
 							 RelationGetRelationName(scan->indexRelation))));
 	}
 
+	MemoryContextSwitchTo(oldCtx);
+
 	pgstat_count_index_scan(scan->indexRelation);
 }
 
@@ -445,6 +447,7 @@ ginendscan(PG_FUNCTION_ARGS)
 	ginFreeScanKeys(so);
 
 	MemoryContextDelete(so->tempCtx);
+	MemoryContextDelete(so->keyCtx);
 
 	pfree(so);
 

src/include/access/gin_private.h

@@ -888,6 +888,8 @@ typedef struct GinScanOpaqueData
 	uint32		totalentries;
 	uint32		allocentries;	/* allocated length of entries[] */
 
+	MemoryContext keyCtx;		/* used to hold key and entry data */
+
 	bool		isVoidRes;		/* true if query is unsatisfiable */
 } GinScanOpaqueData;