Fix shifting base lower: don't let base value get less than zero.

Alexander Korotkov · Alexander Korotkov · commit a4ef2080693e · 2017-12-13T19:42:41.000+03:00
diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
@@ -2939,6 +2939,9 @@ heap_page_prepare_for_xid(Relation relation, Buffer buffer,
 			int64	freeDelta = MaxShortTransactionId - max,
 					requiredDelta = (base + FirstNormalTransactionId) - xid;
 
+			/* Shouldn't consider setting base less than 0 */
+			freeDelta = Min(freeDelta, base);
+
 			if (requiredDelta <= freeDelta)
 			{
 				int64	delta = - (freeDelta + requiredDelta) / 2;

Original file line number	Diff line number	Diff line change
`@@ -2939,6 +2939,9 @@ heap_page_prepare_for_xid(Relation relation, Buffer buffer,`
`2939`	`2939`	`int64 freeDelta = MaxShortTransactionId - max,`
`2940`	`2940`	`requiredDelta = (base + FirstNormalTransactionId) - xid;`
`2941`	`2941`
	`2942`	`+ /* Shouldn't consider setting base less than 0 */`
	`2943`	`+ freeDelta = Min(freeDelta, base);`
	`2944`	`+`
`2942`	`2945`	`if (requiredDelta <= freeDelta)`
`2943`	`2946`	`{`
`2944`	`2947`	`int64 delta = - (freeDelta + requiredDelta) / 2;`