Introduce traversalValue for SP-GiST scan

During scan sometimes it would be very helpful to know some information about
parent node or all 	ancestor nodes. Right now reconstructedValue could be used
but it's not a right usage of it (range opclass uses that).

traversalValue is arbitrary piece of memory in separate MemoryContext while
reconstructedVale should have the same type as indexed column.

Subsequent patches for range opclass and quad4d tree will use it.

Author: Alexander Lebedev, Teodor Sigaev

1 files changed, 18 insertions, 0 deletions

diff --git a/src/backend/access/spgist/spgscan.c b/src/backend/access/spgist/spgscan.c
index 620e7461998..8aa28ecbc39 100644
--- a/src/backend/access/spgist/spgscan.c
+++ b/src/backend/access/spgist/spgscan.c
@@ -30,6 +30,7 @@ typedef void (*storeRes_func) (SpGistScanOpaque so, ItemPointer heapPtr,
 typedef struct ScanStackEntry
 {
 	Datum		reconstructedValue;		/* value reconstructed from parent */
+	void	   *traversalValue; /* opclass-specific traverse value */
 	int			level;			/* level of items on this page */
 	ItemPointerData ptr;		/* block and offset to scan from */
 } ScanStackEntry;
@@ -42,6 +43,9 @@ freeScanStackEntry(SpGistScanOpaque so, ScanStackEntry *stackEntry)
 	if (!so->state.attType.attbyval &&
 		DatumGetPointer(stackEntry->reconstructedValue) != NULL)
 		pfree(DatumGetPointer(stackEntry->reconstructedValue));
+	if (stackEntry->traversalValue)
+		pfree(stackEntry->traversalValue);
+
 	pfree(stackEntry);
 }
 
@@ -239,6 +243,7 @@ static bool
 spgLeafTest(Relation index, SpGistScanOpaque so,
 			SpGistLeafTuple leafTuple, bool isnull,
 			int level, Datum reconstructedValue,
+			void *traversalValue,
 			Datum *leafValue, bool *recheck)
 {
 	bool		result;
@@ -265,6 +270,7 @@ spgLeafTest(Relation index, SpGistScanOpaque so,
 	in.scankeys = so->keyData;
 	in.nkeys = so->numberOfKeys;
 	in.reconstructedValue = reconstructedValue;
+	in.traversalValue = traversalValue;
 	in.level = level;
 	in.returnData = so->want_itup;
 	in.leafDatum = leafDatum;
@@ -365,6 +371,7 @@ redirect:
 									leafTuple, isnull,
 									stackEntry->level,
 									stackEntry->reconstructedValue,
+									stackEntry->traversalValue,
 									&leafValue,
 									&recheck))
 					{
@@ -411,6 +418,7 @@ redirect:
 									leafTuple, isnull,
 									stackEntry->level,
 									stackEntry->reconstructedValue,
+									stackEntry->traversalValue,
 									&leafValue,
 									&recheck))
 					{
@@ -456,6 +464,8 @@ redirect:
 			in.scankeys = so->keyData;
 			in.nkeys = so->numberOfKeys;
 			in.reconstructedValue = stackEntry->reconstructedValue;
+			in.traversalMemoryContext = oldCtx;
+			in.traversalValue = stackEntry->traversalValue;
 			in.level = stackEntry->level;
 			in.returnData = so->want_itup;
 			in.allTheSame = innerTuple->allTheSame;
@@ -523,6 +533,14 @@ redirect:
 					else
 						newEntry->reconstructedValue = (Datum) 0;
 
+					/*
+					 * Elements of out.traversalValues should be allocated in
+					 * in.traversalMemoryContext, which is actually a long
+					 * lived context of index scan.
+					 */
+					newEntry->traversalValue = (out.traversalValues) ?
+						out.traversalValues[i] : NULL;
+
 					so->scanStack = lcons(newEntry, so->scanStack);
 				}
 			}