Add more error reporting during base shift.

Author: Alexander Korotkov

src/backend/access/heap/heapam.c

@@ -2909,6 +2909,19 @@ heap_page_prepare_for_xid(Relation relation, Buffer buffer,
 
 			delta = (int64) (xid - FirstNormalTransactionId) - (int64) base;
 
+			if (xid < base + delta + FirstNormalTransactionId ||
+				xid > base + delta + MaxShortTransactionId)
+			{
+				elog(FATAL, "Fatal xid base calculation error: "
+					"xid = " XID_FMT ", "
+					"base = " XID_FMT ", "
+					"min = %u, "
+					"max = %u, "
+					"delta = " INT64_FORMAT,
+					xid, base, min, max, delta
+				);
+			}
+
 			Assert(xid >= base + delta + FirstNormalTransactionId);
 			Assert(xid <= base + delta + MaxShortTransactionId);
 
@@ -2967,6 +2980,21 @@ heap_page_prepare_for_xid(Relation relation, Buffer buffer,
 			{
 				int64	delta = (freeDelta + requiredDelta) / 2;
 
+				if (xid < base + delta + FirstNormalTransactionId ||
+					xid > base + delta + MaxShortTransactionId)
+				{
+					elog(FATAL, "Fatal xid base calculation error: "
+						"xid = " XID_FMT ", "
+						"base = " XID_FMT ", "
+						"min = %u, "
+						"max = %u, "
+						"freeDelta = " INT64_FORMAT ", "
+						"requiredDelta = " INT64_FORMAT ", "
+						"delta = " INT64_FORMAT,
+						xid, base, min, max, freeDelta, requiredDelta, delta
+					);
+				}
+
 				Assert(xid >= base + delta + FirstNormalTransactionId);
 				Assert(xid <= base + delta + MaxShortTransactionId);