1 files changed, 67 insertions, 3 deletions

diff --git a/src/backend/access/nbtree/nbtsearch.c b/src/backend/access/nbtree/nbtsearch.c
index 17ad89749d5..c47eaed0e98 100644
--- a/src/backend/access/nbtree/nbtsearch.c
+++ b/src/backend/access/nbtree/nbtsearch.c
@@ -1429,6 +1429,7 @@ _bt_first(IndexScanDesc scan, ScanDirection dir)
 	/* remember which buffer we have pinned, if any */
 	Assert(!BTScanPosIsValid(so->currPos));
 	so->currPos.buf = buf;
+	so->firstPage = true;
 
 	/*
 	 * Now load data from the first page of the scan.
@@ -1539,6 +1540,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	int			itemIndex;
 	bool		continuescan;
 	int			indnatts;
+	bool		requiredMatchedByPrecheck;
 
 	/*
 	 * We must have the buffer pinned and locked, but the usual macro can't be
@@ -1592,6 +1594,46 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 	 */
 	Assert(BTScanPosIsPinned(so->currPos));
 
+	/*
+	 * Prechecking the page with scan keys required for direction scan.  We
+	 * check these keys with the last item on the page (according to our scan
+	 * direction).  If these keys are matched, we can skip checking them with
+	 * every item on the page.  Scan keys for our scan direction would
+	 * necessarily match the previous items.  Scan keys required for opposite
+	 * direction scan are already matched by the _bt_first() call.
+	 *
+	 * With the forward scan, we do this check for the last item on the page
+	 * instead of the high key.  It's relatively likely that the most
+	 * significant column in the high key will be different from the
+	 * corresponding value from the last item on the page.  So checking with
+	 * the last item on the page would give a more precise answer.
+	 *
+	 * We skip this for the first page in the scan to evade the possible
+	 * slowdown of the point queries.
+	 */
+	if (!so->firstPage && minoff < maxoff)
+	{
+		ItemId		iid;
+		IndexTuple	itup;
+
+		iid = PageGetItemId(page, ScanDirectionIsForward(dir) ? maxoff : minoff);
+		itup = (IndexTuple) PageGetItem(page, iid);
+
+		/*
+		 * Do the precheck.  Note that we pass the pointer to
+		 * 'requiredMatchedByPrecheck' to 'continuescan' argument.  That will
+		 * set flag to true if all required keys are satisfied and false
+		 * otherwise.
+		 */
+		(void) _bt_checkkeys(scan, itup, indnatts, dir,
+							 &requiredMatchedByPrecheck, false);
+	}
+	else
+	{
+		so->firstPage = false;
+		requiredMatchedByPrecheck = false;
+	}
+
 	if (ScanDirectionIsForward(dir))
 	{
 		/* load items[] in ascending order */
@@ -1603,6 +1645,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 		{
 			ItemId		iid = PageGetItemId(page, offnum);
 			IndexTuple	itup;
+			bool		passes_quals;
 
 			/*
 			 * If the scan specifies not to return killed tuples, then we
@@ -1616,7 +1659,18 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 
 			itup = (IndexTuple) PageGetItem(page, iid);
 
-			if (_bt_checkkeys(scan, itup, indnatts, dir, &continuescan))
+			passes_quals = _bt_checkkeys(scan, itup, indnatts, dir,
+										 &continuescan, requiredMatchedByPrecheck);
+
+			/*
+			 * If the result of prechecking required keys was true, then in
+			 * assert-enabled builds we also recheck that _bt_checkkeys()
+			 * result is is the same.
+			 */
+			Assert(!requiredMatchedByPrecheck ||
+				   passes_quals == _bt_checkkeys(scan, itup, indnatts, dir,
+												 &continuescan, false));
+			if (passes_quals)
 			{
 				/* tuple passes all scan key conditions */
 				if (!BTreeTupleIsPosting(itup))
@@ -1673,7 +1727,7 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			int			truncatt;
 
 			truncatt = BTreeTupleGetNAtts(itup, scan->indexRelation);
-			_bt_checkkeys(scan, itup, truncatt, dir, &continuescan);
+			_bt_checkkeys(scan, itup, truncatt, dir, &continuescan, false);
 		}
 
 		if (!continuescan)
@@ -1725,7 +1779,16 @@ _bt_readpage(IndexScanDesc scan, ScanDirection dir, OffsetNumber offnum)
 			itup = (IndexTuple) PageGetItem(page, iid);
 
 			passes_quals = _bt_checkkeys(scan, itup, indnatts, dir,
-										 &continuescan);
+										 &continuescan, requiredMatchedByPrecheck);
+
+			/*
+			 * If the result of prechecking required keys was true, then in
+			 * assert-enabled builds we also recheck that _bt_checkkeys()
+			 * result is is the same.
+			 */
+			Assert(!requiredMatchedByPrecheck ||
+				   passes_quals == _bt_checkkeys(scan, itup, indnatts, dir,
+												 &continuescan, false));
 			if (passes_quals && tuple_alive)
 			{
 				/* tuple passes all scan key conditions */
@@ -2443,6 +2506,7 @@ _bt_endpoint(IndexScanDesc scan, ScanDirection dir)
 
 	/* remember which buffer we have pinned */
 	so->currPos.buf = buf;
+	so->firstPage = true;
 
 	_bt_initialize_more_data(so, dir);