Support GiST index support functions that want to cache data across calls.

pg_trgm was already doing this unofficially, but the implementation hadn't
been thought through very well and leaked memory.  Restructure the core
GiST code so that it actually works, and document it.  Ordinarily this
would have required an extra memory context creation/destruction for each
GiST index search, but I was able to avoid that in the normal case of a
non-rescanned search by finessing the handling of the RBTree.  It used to
have its own context always, but now shares a context with the
scan-lifespan data structures, unless there is more than one rescan call.
This should make the added overhead unnoticeable in typical cases.

1 files changed, 21 insertions, 21 deletions

diff --git a/src/backend/access/gist/gistbuild.c b/src/backend/access/gist/gistbuild.c
index 0046c7b3ab3..be1b202d39d 100644
--- a/src/backend/access/gist/gistbuild.c
+++ b/src/backend/access/gist/gistbuild.c
@@ -54,7 +54,7 @@ typedef enum
 typedef struct
 {
 	Relation	indexrel;
-	GISTSTATE	giststate;
+	GISTSTATE  *giststate;
 	GISTBuildBuffers *gfbb;
 
 	int64		indtuples;		/* number of tuples indexed */
@@ -63,7 +63,6 @@ typedef struct
 	Size		freespace;		/* amount of free space to leave on pages */
 
 	GistBufferingMode bufferingMode;
-	MemoryContext tmpCtx;
 } GISTBuildState;
 
 static void gistInitBuffering(GISTBuildState *buildstate);
@@ -146,7 +145,14 @@ gistbuild(PG_FUNCTION_ARGS)
 			 RelationGetRelationName(index));
 
 	/* no locking is needed */
-	initGISTstate(&buildstate.giststate, index);
+	buildstate.giststate = initGISTstate(index);
+
+	/*
+	 * Create a temporary memory context that is reset once for each tuple
+	 * processed.  (Note: we don't bother to make this a child of the
+	 * giststate's scanCxt, so we have to delete it separately at the end.)
+	 */
+	buildstate.giststate->tempCxt = createTempGistContext();
 
 	/* initialize the root page */
 	buffer = gistNewBuffer(index);
@@ -185,12 +191,6 @@ gistbuild(PG_FUNCTION_ARGS)
 	buildstate.indtuplesSize = 0;
 
 	/*
-	 * create a temporary memory context that is reset once for each tuple
-	 * processed.
-	 */
-	buildstate.tmpCtx = createTempGistContext();
-
-	/*
 	 * Do the heap scan.
 	 */
 	reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
@@ -208,9 +208,9 @@ gistbuild(PG_FUNCTION_ARGS)
 
 	/* okay, all heap tuples are indexed */
 	MemoryContextSwitchTo(oldcxt);
-	MemoryContextDelete(buildstate.tmpCtx);
+	MemoryContextDelete(buildstate.giststate->tempCxt);
 
-	freeGISTstate(&buildstate.giststate);
+	freeGISTstate(buildstate.giststate);
 
 	/*
 	 * Return statistics
@@ -440,10 +440,10 @@ gistBuildCallback(Relation index,
 	IndexTuple	itup;
 	MemoryContext oldCtx;
 
-	oldCtx = MemoryContextSwitchTo(buildstate->tmpCtx);
+	oldCtx = MemoryContextSwitchTo(buildstate->giststate->tempCxt);
 
 	/* form an index tuple and point it at the heap tuple */
-	itup = gistFormTuple(&buildstate->giststate, index, values, isnull, true);
+	itup = gistFormTuple(buildstate->giststate, index, values, isnull, true);
 	itup->t_tid = htup->t_self;
 
 	if (buildstate->bufferingMode == GIST_BUFFERING_ACTIVE)
@@ -458,7 +458,7 @@ gistBuildCallback(Relation index,
 		 * locked, we call gistdoinsert directly.
 		 */
 		gistdoinsert(index, itup, buildstate->freespace,
-					 &buildstate->giststate);
+					 buildstate->giststate);
 	}
 
 	/* Update tuple count and total size. */
@@ -466,7 +466,7 @@ gistBuildCallback(Relation index,
 	buildstate->indtuplesSize += IndexTupleSize(itup);
 
 	MemoryContextSwitchTo(oldCtx);
-	MemoryContextReset(buildstate->tmpCtx);
+	MemoryContextReset(buildstate->giststate->tempCxt);
 
 	if (buildstate->bufferingMode == GIST_BUFFERING_ACTIVE &&
 		buildstate->indtuples % BUFFERING_MODE_TUPLE_SIZE_STATS_TARGET == 0)
@@ -520,7 +520,7 @@ static bool
 gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
 				GISTBufferingInsertStack *startparent)
 {
-	GISTSTATE  *giststate = &buildstate->giststate;
+	GISTSTATE  *giststate = buildstate->giststate;
 	GISTBuildBuffers *gfbb = buildstate->gfbb;
 	Relation	indexrel = buildstate->indexrel;
 	GISTBufferingInsertStack *path;
@@ -652,7 +652,7 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
 
 	is_split = gistplacetopage(buildstate->indexrel,
 							   buildstate->freespace,
-							   &buildstate->giststate,
+							   buildstate->giststate,
 							   buffer,
 							   itup, ntup, oldoffnum,
 							   InvalidBuffer,
@@ -720,7 +720,7 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
 		 * buffers that will eventually be inserted to them.
 		 */
 		gistRelocateBuildBuffersOnSplit(gfbb,
-										&buildstate->giststate,
+										buildstate->giststate,
 										buildstate->indexrel,
 										path, buffer, splitinfo);
 
@@ -919,7 +919,7 @@ gistProcessEmptyingQueue(GISTBuildState *buildstate)
 			}
 
 			/* Free all the memory allocated during index tuple processing */
-			MemoryContextReset(CurrentMemoryContext);
+			MemoryContextReset(buildstate->giststate->tempCxt);
 		}
 	}
 }
@@ -938,7 +938,7 @@ gistEmptyAllBuffers(GISTBuildState *buildstate)
 	MemoryContext oldCtx;
 	int			i;
 
-	oldCtx = MemoryContextSwitchTo(buildstate->tmpCtx);
+	oldCtx = MemoryContextSwitchTo(buildstate->giststate->tempCxt);
 
 	/*
 	 * Iterate through the levels from top to bottom.
@@ -970,7 +970,7 @@ gistEmptyAllBuffers(GISTBuildState *buildstate)
 					nodeBuffer->queuedForEmptying = true;
 					gfbb->bufferEmptyingQueue =
 						lcons(nodeBuffer, gfbb->bufferEmptyingQueue);
-					MemoryContextSwitchTo(buildstate->tmpCtx);
+					MemoryContextSwitchTo(buildstate->giststate->tempCxt);
 				}
 				gistProcessEmptyingQueue(buildstate);
 			}