On 11.02.2025 20:41, Robert Haas wrote:
On Tue, Feb 11, 2025 at 12:14 PM Andrei Lepikhov <lepi...@gmail.com> wrote:
I support the idea in general, but I believe it should be expanded to
cover all cases of parameterised plan nodes. Each rescan iteration may
produce a different number of tuples, and rounding can obscure important
data.
For example, consider five loops of a scan node: the first loop returns
nine tuples, and each other - zero tuples. When we calculate the
average, 9 divided by 5 equals 1.8. This results in an explanation that
indicates "rows = 1," masking almost 40% of the data.
Now, if we apply the same two loops but have a total of 900,000 tuples,
then 400,000 masked tuples represent a significant portion of the data.
Moreover, switching to a floating-point type for row explanations in
each parameterised node would provide a more comprehensive view and add
valuable information about the parameterisation of the node, which may
not be immediately apparent.
I agree strongly with all of this. I believe we should just implement
what was agreed here:
https://www.postgresql.org/message-id/21013.1243618236%40sss.pgh.pa.us
Let's just display 2 fractional digits when nloops>1, else 0, and call it good.
Thank you for your review!
With such example, it's hard to disagree with it. This would really add
valuable information. Taking all opinions into account, I have updated
the patch v8. I have also included a check for the case where there are
only zeros after the decimal point. We do not want to clutter the rows
with unnecessary zeros.
--
Best regards,
Ilia Evdokimov,
Tantor Labs LLC.
From e1a46d3fa5a4d20b6ea4728b2a3955f375539295 Mon Sep 17 00:00:00 2001
From: Ilia Evdokimov <ilya.evdoki...@tantorlabs.com>
Date: Tue, 11 Feb 2025 22:12:41 +0300
Subject: [PATCH] Clarify display of rows as decimal fractions
When loops > 1, the average rows value is shown as decimal fractions
with two digits after the decimal point in EXPLAIN ANALYZE.
---
doc/src/sgml/perform.sgml | 2 +
src/backend/commands/explain.c | 55 +++++++++++++------
src/test/regress/expected/partition_prune.out | 18 +++---
src/test/regress/sql/partition_prune.sql | 2 +-
4 files changed, 51 insertions(+), 26 deletions(-)
diff --git a/doc/src/sgml/perform.sgml b/doc/src/sgml/perform.sgml
index a502a2aaba..a01832040c 100644
--- a/doc/src/sgml/perform.sgml
+++ b/doc/src/sgml/perform.sgml
@@ -758,6 +758,8 @@ WHERE t1.unique1 < 10 AND t1.unique2 = t2.unique2;
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>.
+ If <literal>loops</literal> is greater than 1,
+ the <literal>rows</literal> is shown as a decimal unless it's an integer.
</para>
<para>
diff --git a/src/backend/commands/explain.c b/src/backend/commands/explain.c
index c24e66f82e..ae81aeea13 100644
--- a/src/backend/commands/explain.c
+++ b/src/backend/commands/explain.c
@@ -13,6 +13,8 @@
*/
#include "postgres.h"
+#include <math.h>
+
#include "access/xact.h"
#include "catalog/pg_type.h"
#include "commands/createas.h"
@@ -69,6 +71,9 @@ typedef struct SerializeMetrics
*/
#define BYTES_TO_KILOBYTES(b) (((b) + 1023) / 1024)
+/* Check if float/double has any decimal number */
+#define HAS_DECIMAL(x) (floor(x) != x)
+
static void ExplainOneQuery(Query *query, int cursorOptions,
IntoClause *into, ExplainState *es,
ParseState *pstate, ParamListInfo params);
@@ -1981,14 +1986,15 @@ ExplainNode(PlanState *planstate, List *ancestors,
if (es->format == EXPLAIN_FORMAT_TEXT)
{
+ appendStringInfo(es->str, " (actual ");
+
if (es->timing)
- appendStringInfo(es->str,
- " (actual time=%.3f..%.3f rows=%.0f loops=%.0f)",
- startup_ms, total_ms, rows, nloops);
+ appendStringInfo(es->str, "time=%.3f..%.3f ", startup_ms, total_ms);
+
+ if (nloops > 1 && HAS_DECIMAL(rows))
+ appendStringInfo(es->str, "rows=%.2f loops=%.0f)", rows, nloops);
else
- appendStringInfo(es->str,
- " (actual rows=%.0f loops=%.0f)",
- rows, nloops);
+ appendStringInfo(es->str, "rows=%.0f loops=%.0f)", rows, nloops);
}
else
{
@@ -1999,8 +2005,16 @@ ExplainNode(PlanState *planstate, List *ancestors,
ExplainPropertyFloat("Actual Total Time", "ms", total_ms,
3, es);
}
- ExplainPropertyFloat("Actual Rows", NULL, rows, 0, es);
- ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+ if (nloops > 1 && HAS_DECIMAL(rows))
+ {
+ ExplainPropertyFloat("Actual Rows", NULL, rows, 2, es);
+ ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+ }
+ else
+ {
+ ExplainPropertyFloat("Actual Rows", NULL, rows, 0, es);
+ ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+ }
}
}
else if (es->analyze)
@@ -2052,14 +2066,14 @@ ExplainNode(PlanState *planstate, List *ancestors,
if (es->format == EXPLAIN_FORMAT_TEXT)
{
ExplainIndentText(es);
+ appendStringInfo(es->str, "actual ");
if (es->timing)
- appendStringInfo(es->str,
- "actual time=%.3f..%.3f rows=%.0f loops=%.0f\n",
- startup_ms, total_ms, rows, nloops);
+ appendStringInfo(es->str, "time=%.3f..%.3f", startup_ms, total_ms);
+
+ if (nloops > 1 && HAS_DECIMAL(rows))
+ appendStringInfo(es->str, "rows=%.2f loops=%.0f\n", rows, nloops);
else
- appendStringInfo(es->str,
- "actual rows=%.0f loops=%.0f\n",
- rows, nloops);
+ appendStringInfo(es->str, "rows=%.0f loops=%.0f\n", rows, nloops);
}
else
{
@@ -2070,8 +2084,17 @@ ExplainNode(PlanState *planstate, List *ancestors,
ExplainPropertyFloat("Actual Total Time", "ms",
total_ms, 3, es);
}
- ExplainPropertyFloat("Actual Rows", NULL, rows, 0, es);
- ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+
+ if (nloops > 1 && HAS_DECIMAL(rows))
+ {
+ ExplainPropertyFloat("Actual Rows", NULL, rows, 2, es);
+ ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+ }
+ else
+ {
+ ExplainPropertyFloat("Actual Rows", NULL, rows, 0, es);
+ ExplainPropertyFloat("Actual Loops", NULL, nloops, 0, es);
+ }
}
ExplainCloseWorker(n, es);
diff --git a/src/test/regress/expected/partition_prune.out b/src/test/regress/expected/partition_prune.out
index e667503c96..fde44db1a0 100644
--- a/src/test/regress/expected/partition_prune.out
+++ b/src/test/regress/expected/partition_prune.out
@@ -2367,7 +2367,7 @@ begin
$1)
loop
ln := regexp_replace(ln, 'Workers Launched: \d+', 'Workers Launched: N');
- ln := regexp_replace(ln, 'actual rows=\d+ loops=\d+', 'actual rows=N loops=N');
+ ln := regexp_replace(ln, 'actual rows=\d+(?:\.\d+)? loops=\d+', 'actual rows=N loops=N');
ln := regexp_replace(ln, 'Rows Removed by Filter: \d+', 'Rows Removed by Filter: N');
return next ln;
end loop;
@@ -3049,14 +3049,14 @@ order by tbl1.col1, tprt.col1;
insert into tbl1 values (1001), (1010), (1011);
explain (analyze, costs off, summary off, timing off, buffers off)
select * from tbl1 inner join tprt on tbl1.col1 > tprt.col1;
- QUERY PLAN
---------------------------------------------------------------------------
+ QUERY PLAN
+-----------------------------------------------------------------------------
Nested Loop (actual rows=23 loops=1)
-> Seq Scan on tbl1 (actual rows=5 loops=1)
- -> Append (actual rows=5 loops=5)
+ -> Append (actual rows=4.60 loops=5)
-> Index Scan using tprt1_idx on tprt_1 (actual rows=2 loops=5)
Index Cond: (col1 < tbl1.col1)
- -> Index Scan using tprt2_idx on tprt_2 (actual rows=3 loops=4)
+ -> Index Scan using tprt2_idx on tprt_2 (actual rows=2.75 loops=4)
Index Cond: (col1 < tbl1.col1)
-> Index Scan using tprt3_idx on tprt_3 (actual rows=1 loops=2)
Index Cond: (col1 < tbl1.col1)
@@ -3070,16 +3070,16 @@ select * from tbl1 inner join tprt on tbl1.col1 > tprt.col1;
explain (analyze, costs off, summary off, timing off, buffers off)
select * from tbl1 inner join tprt on tbl1.col1 = tprt.col1;
- QUERY PLAN
---------------------------------------------------------------------------
+ QUERY PLAN
+-----------------------------------------------------------------------------
Nested Loop (actual rows=3 loops=1)
-> Seq Scan on tbl1 (actual rows=5 loops=1)
- -> Append (actual rows=1 loops=5)
+ -> Append (actual rows=0.60 loops=5)
-> Index Scan using tprt1_idx on tprt_1 (never executed)
Index Cond: (col1 = tbl1.col1)
-> Index Scan using tprt2_idx on tprt_2 (actual rows=1 loops=2)
Index Cond: (col1 = tbl1.col1)
- -> Index Scan using tprt3_idx on tprt_3 (actual rows=0 loops=3)
+ -> Index Scan using tprt3_idx on tprt_3 (actual rows=0.33 loops=3)
Index Cond: (col1 = tbl1.col1)
-> Index Scan using tprt4_idx on tprt_4 (never executed)
Index Cond: (col1 = tbl1.col1)
diff --git a/src/test/regress/sql/partition_prune.sql b/src/test/regress/sql/partition_prune.sql
index 730545e86a..58756e0b18 100644
--- a/src/test/regress/sql/partition_prune.sql
+++ b/src/test/regress/sql/partition_prune.sql
@@ -586,7 +586,7 @@ begin
$1)
loop
ln := regexp_replace(ln, 'Workers Launched: \d+', 'Workers Launched: N');
- ln := regexp_replace(ln, 'actual rows=\d+ loops=\d+', 'actual rows=N loops=N');
+ ln := regexp_replace(ln, 'actual rows=\d+(?:\.\d+)? loops=\d+', 'actual rows=N loops=N');
ln := regexp_replace(ln, 'Rows Removed by Filter: \d+', 'Rows Removed by Filter: N');
return next ln;
end loop;
--
2.34.1
