Fix GiST index deletion assert issue.

petergeoghegan · petergeoghegan · commit e42b3c3bd6a9 · 2021-01-26T23:24:37.000-08:00
Avoid calling heap_index_delete_tuples() with an empty deltids array to avoid an assertion failure. This issue was arguably an oversight in commit b5f58cf, though the failing assert itself was added by my recent commit d168b66. No backpatch, though, since the oversight is harmless in the back branches. Author: Peter Geoghegan <pg@bowt.ie> Reported-By: Jaime Casanova <jcasanov@systemguards.com.ec> Discussion: https://postgr.es/m/CAJKUy5jscES84n3puE=sYngyF+zpb4wv8UMtuLnLPv5z=6yyNw@mail.gmail.com
diff --git a/src/backend/access/gist/gist.c b/src/backend/access/gist/gist.c
@@ -1645,7 +1645,6 @@ gistprunepage(Relation rel, Page page, Buffer buffer, Relation heapRel)
 	int			ndeletable = 0;
 	OffsetNumber offnum,
 				maxoff;
-	TransactionId latestRemovedXid = InvalidTransactionId;
 
 	Assert(GistPageIsLeaf(page));
 
@@ -1664,13 +1663,15 @@ gistprunepage(Relation rel, Page page, Buffer buffer, Relation heapRel)
 			deletable[ndeletable++] = offnum;
 	}
 
-	if (XLogStandbyInfoActive() && RelationNeedsWAL(rel))
-		latestRemovedXid =
-			index_compute_xid_horizon_for_tuples(rel, heapRel, buffer,
-												 deletable, ndeletable);
-
 	if (ndeletable > 0)
 	{
+		TransactionId latestRemovedXid = InvalidTransactionId;
+
+		if (XLogStandbyInfoActive() && RelationNeedsWAL(rel))
+			latestRemovedXid =
+				index_compute_xid_horizon_for_tuples(rel, heapRel, buffer,
+													 deletable, ndeletable);
+
 		START_CRIT_SECTION();
 
 		PageIndexMultiDelete(page, deletable, ndeletable);
diff --git a/src/backend/access/index/genam.c b/src/backend/access/index/genam.c
@@ -301,6 +301,8 @@ index_compute_xid_horizon_for_tuples(Relation irel,
 	Page		ipage = BufferGetPage(ibuf);
 	IndexTuple	itup;
 
+	Assert(nitems > 0);
+
 	delstate.bottomup = false;
 	delstate.bottomupfreespace = 0;
 	delstate.ndeltids = 0;
