Fix comment about promising tuples.

Oversight in commit d168b666823, which added bottom-up index deletion.

diff --git a/src/backend/access/heap/heapam.c b/src/backend/access/heap/heapam.c
index 3b435c107d0c6c213c345eb2a3f7c4a9642fe7fe..7cb87f4a3b316befbb11b77ec79bf67ad67507fd 100644 (file)
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -7879,8 +7879,10 @@ bottomup_sort_and_shrink(TM_IndexDeleteOp *delstate)
    /*
     * We're about ready to sort block groups to determine the optimal order
     * for visiting heap blocks.  But before we do, round the number of
-    * promising tuples for each block group up to the nearest power-of-two
-    * (except for block groups where npromisingtids is already 0).
+    * promising tuples for each block group up to the next power-of-two,
+    * unless it is very low (less than 4), in which case we round up to 4.
+    * npromisingtids is far too noisy to trust when choosing between a pair
+    * of block groups that both have very low values.
     *
     * This scheme divides heap blocks/block groups into buckets.  Each bucket
     * contains blocks that have _approximately_ the same number of promising