From 766e8bf46a415cf3c4e3a4c94a2479ea91d3e93f Mon Sep 17 00:00:00 2001 From: Ilia Evdokimov Date: Mon, 17 Feb 2025 21:22:11 +0300 Subject: [PATCH v11 2/2] 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 | 39 ++++++++++++++++++++------------------- 1 file changed, 20 insertions(+), 19 deletions(-) diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml index a502a2aaba..588ee6d5aa 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); EXPLAIN ANALYZE SELECT * FROM tenk1 t1, tenk2 t2 -WHERE t1.unique1 < 10 AND t1.unique2 = t2.unique2; +WHERE t1.thousand < 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 - -> 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 < 10) - Heap Blocks: exact=10 - Buffers: shared hit=3 read=5 written=4 - -> 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 < 10) + 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 + -> 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 < 10) + Heap Blocks: exact=90 + Buffers: shared hit=92 + -> 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 < 10) Buffers: shared hit=2 - -> 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 + -> 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 < 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 Note that the actual time values are in milliseconds of @@ -756,8 +756,9 @@ WHERE t1.unique1 < 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 loops 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 tenk2. + 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 tenk2. -- 2.34.1