v9-0001-Clarify-display-of-rows-as-decimal-fractions-DOC.patch

From 789d98383988ef6d3b0bc2c6b9b5c73a83ffd6d4 Mon Sep 17 00:00:00 2001
From: Ilia Evdokimov <ilya.evdokimov@tantorlabs.ru>
Date: Thu, 13 Feb 2025 11:19:03 +0300
Subject: [PATCH v9] Clarify display of rows as decimal fractions

When loops > 1, the average rows value is now displayed as a decimal fraction
with two digits after the decimal point in EXPLAIN ANALYZE.

Previously, the average rows value was always rounded to an integer,
which could lead to misleading results when estimating total rows
by multiplying rows by loop. This change ensures that users
get a more accurate representation of the data flow through execution nodes.
---
 doc/src/sgml/perform.sgml | 41 ++++++++++++++++++++-------------------
 1 file changed, 21 insertions(+), 20 deletions(-)

diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index a502a2aaba..dd61ae4507 100644
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -717,26 +717,26 @@ FROM tenk1 t1 WHERE t1.ten = (SELECT (random() * 10)::integer);
 <screen>
 EXPLAIN ANALYZE SELECT *
 FROM tenk1 t1, tenk2 t2
-WHERE t1.unique1 &lt; 10 AND t1.unique2 = t2.unique2;
-
-                                                           QUERY PLAN
--------------------------------------------------------------------&zwsp;--------------------------------------------------------------
- Nested Loop  (cost=4.65..118.50 rows=10 width=488) (actual time=0.017..0.051 rows=10 loops=1)
-   Buffers: shared hit=36 read=6
-   -&gt;  Bitmap Heap Scan on tenk1 t1  (cost=4.36..39.38 rows=10 width=244) (actual time=0.009..0.017 rows=10 loops=1)
-         Recheck Cond: (unique1 &lt; 10)
-         Heap Blocks: exact=10
-         Buffers: shared hit=3 read=5 written=4
-         -&gt;  Bitmap Index Scan on tenk1_unique1  (cost=0.00..4.36 rows=10 width=0) (actual time=0.004..0.004 rows=10 loops=1)
-               Index Cond: (unique1 &lt; 10)
+WHERE t1.thousand &lt; 10 AND t1.unique2 &gt; t2.unique2;
+
+                                                                 QUERY PLAN
+-------------------------------------------------------------------&zwsp;-------------------------------------------------------------------------
+ Nested Loop  (cost=5.40..11571.44 rows=356667 width=488) (actual time=0.042..117.205 rows=513832 loops=1)
+   Buffers: shared hit=19377 read=29
+   -&gt;  Bitmap Heap Scan on tenk1 t1  (cost=5.11..233.60 rows=107 width=244) (actual time=0.021..0.103 rows=100 loops=1)
+         Recheck Cond: (thousand &lt; 10)
+         Heap Blocks: exact=90
+         Buffers: shared hit=92
+         -&gt;  Bitmap Index Scan on tenk1_thous_tenthous  (cost=0.00..5.09 rows=107 width=0) (actual time=0.010..0.010 rows=100 loops=1)
+               Index Cond: (thousand &lt; 10)
                Buffers: shared hit=2
-   -&gt;  Index Scan using tenk2_unique2 on tenk2 t2  (cost=0.29..7.90 rows=1 width=244) (actual time=0.003..0.003 rows=1 loops=10)
-         Index Cond: (unique2 = t1.unique2)
-         Buffers: shared hit=24 read=6
+   -&gt;  Index Scan using tenk2_unique2 on tenk2 t2  (cost=0.29..72.63 rows=3333 width=244) (actual time=0.006..0.410 rows=5138.32 loops=100)
+         Index Cond: (unique2 &lt; t1.unique2)
+         Buffers: shared hit=19285 read=29
  Planning:
-   Buffers: shared hit=15 dirtied=9
- Planning Time: 0.485 ms
- Execution Time: 0.073 ms
+   Buffers: shared hit=258 read=9 dirtied=2
+ Planning Time: 0.519 ms
+ Execution Time: 131.378 ms
 </screen>
 
     Note that the <quote>actual time</quote> values are in milliseconds of
@@ -756,8 +756,9 @@ WHERE t1.unique1 &lt; 10 AND t1.unique2 = t2.unique2;
     values shown are averages per-execution.  This is done to make the numbers
     comparable with the way that the cost estimates are shown.  Multiply by
     the <literal>loops</literal> value to get the total time actually spent in
-    the node.  In the above example, we spent a total of 0.030 milliseconds
-    executing the index scans on <literal>tenk2</literal>.
+    the node, and to get the total rows processed in the node. In the above example,
+    we spent a total of 41 milliseconds executing the index scans,
+    and the node processed a total of 513832 rows on <literal>tenk2</literal>.
    </para>
 
    <para>
-- 
2.34.1