Clarify runtime pruning in EXPLAIN

Author: Amit Langote
Reviewed-by: David Rowley
Discussion: https://postgr.es/m/002dec69-9afb-b621-5630-235eceafe0bd@lab.ntt.co.jp

diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 1925ff45509ceee9a235967dadcf6f5253d233f2..85e435898823ab4d05dafd81c6c89eee1e15a496 100644 (file)
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -4421,8 +4421,12 @@ EXPLAIN SELECT count(*) FROM measurement WHERE logdate >= DATE '2008-01-01';
        query, partition pruning is performed whenever one of the
        execution parameters being used by partition pruning changes.
        Determining if partitions were pruned during this phase requires
-       careful inspection of the nloops property in
-       the EXPLAIN ANALYZE output.
+       careful inspection of the loops property in
+       the EXPLAIN ANALYZE output.  Subplans
+       corresponding to different partitions may have different values
+       for it depending on how many times each of them was pruned during
+       execution.  Some may be shown as (never executed)
+       if they were pruned every time.