simple_getwalavailability_wip.patch

diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index 55cac186dc..0b9cca2173 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9504,62 +9504,29 @@ GetWALAvailability(XLogRecPtr targetLSN)
 	XLogSegNo	currSeg;		/* segid of currpos */
 	XLogSegNo	targetSeg;		/* segid of targetLSN */
 	XLogSegNo	oldestSeg;		/* actual oldest segid */
-	XLogSegNo	oldestSegMaxWalSize;	/* oldest segid kept by max_wal_size */
-	XLogSegNo	oldestSlotSeg = InvalidXLogRecPtr;	/* oldest segid kept by
-													 * slot */
 	uint64		keepSegs;
 
 	/* slot does not reserve WAL. Either deactivated, or has never been active */
 	if (XLogRecPtrIsInvalid(targetLSN))
 		return WALAVAIL_INVALID_LSN;
 
-	currpos = GetXLogWriteRecPtr();
-
 	/* calculate oldest segment currently needed by slots */
 	XLByteToSeg(targetLSN, targetSeg, wal_segment_size);
-	KeepLogSeg(currpos, &oldestSlotSeg);
 
-	/*
-	 * Find the oldest extant segment file. We get 1 until checkpoint removes
-	 * the first WAL segment file since startup, which causes the status being
-	 * wrong under certain abnormal conditions but that doesn't actually harm.
-	 */
-	oldestSeg = XLogGetLastRemovedSegno() + 1;
+	/* Find the oldest extant segment file */
+	oldestSeg = XLogGetLastRemovedSegno();
 
-	/* calculate oldest segment by max_wal_size and wal_keep_segments */
+	if (targetSeg <= oldestSeg)
+		return WALAVAIL_REMOVED;
+
+	currpos = GetXLogWriteRecPtr();
 	XLByteToSeg(currpos, currSeg, wal_segment_size);
-	keepSegs = ConvertToXSegs(Max(max_wal_size_mb, wal_keep_segments),
-							  wal_segment_size) + 1;
+	keepSegs = ConvertToXSegs(max_wal_size_mb, wal_segment_size);
 
-	if (currSeg > keepSegs)
-		oldestSegMaxWalSize = currSeg - keepSegs;
-	else
-		oldestSegMaxWalSize = 1;
-
-	/*
-	 * If max_slot_wal_keep_size has changed after the last call, the segment
-	 * that would been kept by the current setting might have been lost by the
-	 * previous setting. No point in showing normal or keeping status values
-	 * if the targetSeg is known to be lost.
-	 */
-	if (targetSeg >= oldestSeg)
-	{
-		/*
-		 * show "normal" when targetSeg is within max_wal_size, even if
-		 * max_slot_wal_keep_size is smaller than max_wal_size.
-		 */
-		if ((max_slot_wal_keep_size_mb <= 0 ||
-			 max_slot_wal_keep_size_mb >= max_wal_size_mb) &&
-			oldestSegMaxWalSize <= targetSeg)
+	if (currSeg - targetSeg <= keepSegs)
 			return WALAVAIL_NORMAL;
 
-		/* being retained by slots */
-		if (oldestSlotSeg <= targetSeg)
-			return WALAVAIL_RESERVED;
-	}
-
-	/* Definitely lost */
-	return WALAVAIL_REMOVED;
+	return WALAVAIL_RESERVED;
 }