Make non-MVCC snapshots exempt from predicate locking. Scans with non-MVCC

snapshots, like in REINDEX, are basically non-transactional operations. The
DDL operation itself might participate in SSI, but there's separate
functions for that.

Kevin Grittner and Dan Ports, with some changes by me.

3 files changed, 37 insertions, 34 deletions

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 01a492e496..b947c11f7d 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -274,7 +274,8 @@ heapgetpage(HeapScanDesc scan, BlockNumber page)
 			else
 				valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
 
-			CheckForSerializableConflictOut(valid, scan->rs_rd, &loctup, buffer);
+			CheckForSerializableConflictOut(valid, scan->rs_rd, &loctup,
+											buffer, snapshot);
 
 			if (valid)
 				scan->rs_vistuples[ntup++] = lineoff;
@@ -469,7 +470,8 @@ heapgettup(HeapScanDesc scan,
 													 snapshot,
 													 scan->rs_cbuf);
 
-				CheckForSerializableConflictOut(valid, scan->rs_rd, tuple, scan->rs_cbuf);
+				CheckForSerializableConflictOut(valid, scan->rs_rd, tuple,
+												scan->rs_cbuf, snapshot);
 
 				if (valid && key != NULL)
 					HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
@@ -478,7 +480,7 @@ heapgettup(HeapScanDesc scan,
 				if (valid)
 				{
 					if (!scan->rs_relpredicatelocked)
-						PredicateLockTuple(scan->rs_rd, tuple);
+						PredicateLockTuple(scan->rs_rd, tuple, snapshot);
 					LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
 					return;
 				}
@@ -747,7 +749,7 @@ heapgettup_pagemode(HeapScanDesc scan,
 				if (valid)
 				{
 					if (!scan->rs_relpredicatelocked)
-						PredicateLockTuple(scan->rs_rd, tuple);
+						PredicateLockTuple(scan->rs_rd, tuple, scan->rs_snapshot);
 					scan->rs_cindex = lineindex;
 					return;
 				}
@@ -755,7 +757,7 @@ heapgettup_pagemode(HeapScanDesc scan,
 			else
 			{
 				if (!scan->rs_relpredicatelocked)
-					PredicateLockTuple(scan->rs_rd, tuple);
+					PredicateLockTuple(scan->rs_rd, tuple, scan->rs_snapshot);
 				scan->rs_cindex = lineindex;
 				return;
 			}
@@ -1470,9 +1472,9 @@ heap_fetch(Relation relation,
 	valid = HeapTupleSatisfiesVisibility(tuple, snapshot, buffer);
 
 	if (valid)
-		PredicateLockTuple(relation, tuple);
+		PredicateLockTuple(relation, tuple, snapshot);
 
-	CheckForSerializableConflictOut(valid, relation, tuple, buffer);
+	CheckForSerializableConflictOut(valid, relation, tuple, buffer, snapshot);
 
 	LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
 
@@ -1588,11 +1590,12 @@ heap_hot_search_buffer(ItemPointer tid, Relation relation, Buffer buffer,
 
 		/* If it's visible per the snapshot, we must return it */
 		valid = HeapTupleSatisfiesVisibility(&heapTuple, snapshot, buffer);
-		CheckForSerializableConflictOut(valid, relation, &heapTuple, buffer);
+		CheckForSerializableConflictOut(valid, relation, &heapTuple, buffer,
+										snapshot);
 		if (valid)
 		{
 			ItemPointerSetOffsetNumber(tid, offnum);
-			PredicateLockTuple(relation, &heapTuple);
+			PredicateLockTuple(relation, &heapTuple, snapshot);
 			if (all_dead)
 				*all_dead = false;
 			return true;
@@ -1750,7 +1753,7 @@ heap_get_latest_tid(Relation relation,
 		 * result candidate.
 		 */
 		valid = HeapTupleSatisfiesVisibility(&tp, snapshot, buffer);
-		CheckForSerializableConflictOut(valid, relation, &tp, buffer);
+		CheckForSerializableConflictOut(valid, relation, &tp, buffer, snapshot);
 		if (valid)
 			*tid = ctid;
 
diff --git a/src/backend/access/index/indexam.c b/src/backend/access/index/indexam.c
index 0208765964..31d705c056 100644
--- a/src/backend/access/index/indexam.c
+++ b/src/backend/access/index/indexam.c
@@ -126,7 +126,7 @@ do { \
 } while(0)
 
 static IndexScanDesc index_beginscan_internal(Relation indexRelation,
-						 int nkeys, int norderbys);
+						 int nkeys, int norderbys, Snapshot snapshot);
 
 
 /* ----------------------------------------------------------------
@@ -234,7 +234,7 @@ index_beginscan(Relation heapRelation,
 {
 	IndexScanDesc scan;
 
-	scan = index_beginscan_internal(indexRelation, nkeys, norderbys);
+	scan = index_beginscan_internal(indexRelation, nkeys, norderbys, snapshot);
 
 	/*
 	 * Save additional parameters into the scandesc.  Everything else was set
@@ -259,7 +259,7 @@ index_beginscan_bitmap(Relation indexRelation,
 {
 	IndexScanDesc scan;
 
-	scan = index_beginscan_internal(indexRelation, nkeys, 0);
+	scan = index_beginscan_internal(indexRelation, nkeys, 0, snapshot);
 
 	/*
 	 * Save additional parameters into the scandesc.  Everything else was set
@@ -275,7 +275,7 @@ index_beginscan_bitmap(Relation indexRelation,
  */
 static IndexScanDesc
 index_beginscan_internal(Relation indexRelation,
-						 int nkeys, int norderbys)
+						 int nkeys, int norderbys, Snapshot snapshot)
 {
 	IndexScanDesc scan;
 	FmgrInfo   *procedure;
@@ -284,7 +284,7 @@ index_beginscan_internal(Relation indexRelation,
 	GET_REL_PROCEDURE(ambeginscan);
 
 	if (!(indexRelation->rd_am->ampredlocks))
-		PredicateLockRelation(indexRelation);
+		PredicateLockRelation(indexRelation, snapshot);
 
 	/*
 	 * We hold a reference count to the relcache entry throughout the scan.
@@ -602,7 +602,8 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
 												 scan->xs_cbuf);
 
 			CheckForSerializableConflictOut(valid, scan->heapRelation,
-											heapTuple, scan->xs_cbuf);
+											heapTuple, scan->xs_cbuf,
+											scan->xs_snapshot);
 
 			if (valid)
 			{
@@ -624,7 +625,7 @@ index_getnext(IndexScanDesc scan, ScanDirection direction)
 				else
 					scan->xs_next_hot = InvalidOffsetNumber;
 
-				PredicateLockTuple(scan->heapRelation, heapTuple);
+				PredicateLockTuple(scan->heapRelation, heapTuple, scan->xs_snapshot);
 
 				LockBuffer(scan->xs_cbuf, BUFFER_LOCK_UNLOCK);
 
diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 2ce2bc2f00..0771d19463 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -64,10 +64,7 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, bool nextkey,
 
 	/* If index is empty and access = BT_READ, no root page is created. */
 	if (!BufferIsValid(*bufP))
-	{
-		PredicateLockRelation(rel);		/* Nothing finer to lock exists. */
 		return (BTStack) NULL;
-	}
 
 	/* Loop iterates once per level descended in the tree */
 	for (;;)
@@ -92,11 +89,7 @@ _bt_search(Relation rel, int keysz, ScanKey scankey, bool nextkey,
 		page = BufferGetPage(*bufP);
 		opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 		if (P_ISLEAF(opaque))
-		{
-			if (access == BT_READ)
-				PredicateLockPage(rel, BufferGetBlockNumber(*bufP));
 			break;
-		}
 
 		/*
 		 * Find the appropriate item on the internal page, and get the child
@@ -855,9 +848,16 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 
 	if (!BufferIsValid(buf))
 	{
-		/* Only get here if index is completely empty */
+		/*
+		 * We only get here if the index is completely empty.
+		 * Lock relation because nothing finer to lock exists.
+		 */
+		PredicateLockRelation(rel, scan->xs_snapshot);
 		return false;
 	}
+	else
+		PredicateLockPage(rel, BufferGetBlockNumber(buf),
+						  scan->xs_snapshot);
 
 	/* initialize moreLeft/moreRight appropriately for scan direction */
 	if (ScanDirectionIsForward(dir))
@@ -1153,7 +1153,7 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir)
 			opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 			if (!P_IGNORE(opaque))
 			{
-				PredicateLockPage(rel, blkno);
+				PredicateLockPage(rel, blkno, scan->xs_snapshot);
 				/* see if there are any matches on this page */
 				/* note that this will clear moreRight if we can stop */
 				if (_bt_readpage(scan, dir, P_FIRSTDATAKEY(opaque)))
@@ -1201,7 +1201,7 @@ _bt_steppage(IndexScanDesc scan, ScanDirection dir)
 			opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 			if (!P_IGNORE(opaque))
 			{
-				PredicateLockPage(rel, BufferGetBlockNumber(so->currPos.buf));
+				PredicateLockPage(rel, BufferGetBlockNumber(so->currPos.buf), scan->xs_snapshot);
 				/* see if there are any matches on this page */
 				/* note that this will clear moreLeft if we can stop */
 				if (_bt_readpage(scan, dir, PageGetMaxOffsetNumber(page)))
@@ -1363,11 +1363,7 @@ _bt_get_endpoint(Relation rel, uint32 level, bool rightmost)
 		buf = _bt_gettrueroot(rel);
 
 	if (!BufferIsValid(buf))
-	{
-		/* empty index... */
-		PredicateLockRelation(rel);		/* Nothing finer to lock exists. */
 		return InvalidBuffer;
-	}
 
 	page = BufferGetPage(buf);
 	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
@@ -1444,13 +1440,16 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
 
 	if (!BufferIsValid(buf))
 	{
-		/* empty index... */
-		PredicateLockRelation(rel);		/* Nothing finer to lock exists. */
+		/*
+		 * Empty index. Lock the whole relation, as nothing finer to lock
+		 * exists.
+		 */
+		PredicateLockRelation(rel, scan->xs_snapshot);
 		so->currPos.buf = InvalidBuffer;
 		return false;
 	}
 
-	PredicateLockPage(rel, BufferGetBlockNumber(buf));
+	PredicateLockPage(rel, BufferGetBlockNumber(buf), scan->xs_snapshot);
 	page = BufferGetPage(buf);
 	opaque = (BTPageOpaque) PageGetSpecialPointer(page);
 	Assert(P_ISLEAF(opaque));