From e119d74ddd5cd5550246213fc66cd75cae606571 Mon Sep 17 00:00:00 2001
From: Dmitrii Dolgov <9erthalion6@gmail.com>
Date: Mon, 16 Oct 2023 16:52:27 +0200
Subject: [PATCH v15 4/4] Add query_id_const_merge_threshold
Extend query_id_const_merge to allow merging only if the number of
elements is larger than specified value, which could be configured using
new GUC query_id_const_merge_threshold.
---
.../pg_stat_statements/expected/merging.out | 64 +++++++++++++++++++
contrib/pg_stat_statements/sql/merging.sql | 17 +++++
doc/src/sgml/config.sgml | 15 +++++
doc/src/sgml/pgstatstatements.sgml | 6 ++
src/backend/nodes/queryjumblefuncs.c | 12 +++-
src/backend/utils/misc/guc_tables.c | 11 ++++
src/backend/utils/misc/postgresql.conf.sample | 1 +
src/include/nodes/queryjumble.h | 1 +
8 files changed, 126 insertions(+), 1 deletion(-)
diff --git a/contrib/pg_stat_statements/expected/merging.out b/contrib/pg_stat_statements/expected/merging.out
index 1bb75a93045..81811b2db0d 100644
--- a/contrib/pg_stat_statements/expected/merging.out
+++ b/contrib/pg_stat_statements/expected/merging.out
@@ -218,4 +218,68 @@ FROM cte;
--------
(0 rows)
+-- With the threshold
+SET query_id_const_merge_threshold = 10;
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset
+--------------------------
+
+(1 row)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+ id | data
+----+------
+(0 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+ id | data
+----+------
+(0 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+ id | data
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+ query | calls
+---------------------------------------------------------------------------+-------
+ SELECT * FROM test_merge WHERE id IN ($1, $2, $3, $4, $5, $6, $7, $8, $9) | 1
+ SELECT * FROM test_merge WHERE id IN (... [10-99 entries]) | 2
+ SELECT pg_stat_statements_reset() | 1
+(3 rows)
+
+-- With gaps on the threshold
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset
+--------------------------
+
+(1 row)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4);
+ id | data
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+ query | calls
+-------------------------------------------------------+-------
+ SELECT * FROM test_merge WHERE id IN ($1, $2, $3, $4) | 1
+ SELECT pg_stat_statements_reset() | 1
+(2 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15);
+ id | data
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+ query | calls
+------------------------------------------------------------------------+-------
+ SELECT * FROM test_merge WHERE id IN ($1, $2, $3, $4) | 1
+ SELECT * FROM test_merge WHERE id IN (... [10-99 entries]) | 1
+ SELECT pg_stat_statements_reset() | 1
+ SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C" | 1
+(4 rows)
+
RESET query_id_const_merge;
diff --git a/contrib/pg_stat_statements/sql/merging.sql b/contrib/pg_stat_statements/sql/merging.sql
index 75960159a1d..1dc0fef9984 100644
--- a/contrib/pg_stat_statements/sql/merging.sql
+++ b/contrib/pg_stat_statements/sql/merging.sql
@@ -68,4 +68,21 @@ WITH cte AS (
SELECT ARRAY['a', 'b', 'c', const::varchar] AS result
FROM cte;
+-- With the threshold
+SET query_id_const_merge_threshold = 10;
+
+SELECT pg_stat_statements_reset();
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- With gaps on the threshold
+SELECT pg_stat_statements_reset();
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
RESET query_id_const_merge;
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 4fd997284c9..c31d4806c1c 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8219,6 +8219,21 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
+
+ query_id_const_merge_threshold (integer)
+
+ query_id_const_merge_threshold configuration parameter
+
+
+
+
+ If parameter is enabled,
+ specifies the minimal number of element an array must have to apply
+ constants merge.
+
+
+
+
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index 1f6e6a0e76b..eb00c1ecd2a 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -566,6 +566,12 @@ query | SELECT pg_stat_statements_reset()
calls | 1
+ Such constants merging could be configured apply only starting from certain
+ number of constants in the array. The threshold could be specified using
+ .
+
+
+
But there is a small chance of hash collisions causing unrelated queries to
be merged into one entry. (This cannot happen for queries belonging to
different users or databases, however.)
diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
index b198fe2579e..5d3acf1115c 100644
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -47,6 +47,9 @@ int compute_query_id = COMPUTE_QUERY_ID_AUTO;
/* Whether to merge constants in a list when computing query_id */
bool query_id_const_merge = false;
+/* Lower threshold for the list length to merge constants when computing query_id */
+bool query_id_const_merge_threshold = 1;
+
/* True when compute_query_id is ON, or AUTO and a module requests them */
bool query_id_enabled = false;
@@ -227,7 +230,8 @@ RecordConstLocation(JumbleState *jstate, int location, int magnitude)
/*
* Verify if the provided list contains could be merged down, which means it
- * contains only constant expressions.
+ * contains only constant expressions and the list contains more than
+ * query_id_const_merge_threshold elements.
*
* Return value is the order of magnitude (i.e. how many digits it has) for
* length of the list (to use for representation purposes later on) if merging
@@ -251,6 +255,12 @@ IsMergeableConstList(List *elements, Const **firstConst, Const **lastConst)
return 0;
}
+ if (elements->length < query_id_const_merge_threshold)
+ {
+ /* The list is not large enough */
+ return 0;
+ }
+
firstExpr = linitial(elements);
/*
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index fbb50adb9f9..ee239ae7302 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3518,6 +3518,17 @@ struct config_int ConfigureNamesInt[] =
NULL, NULL, NULL
},
+ {
+ {"query_id_const_merge_threshold", PGC_SUSET, STATS_MONITORING,
+ gettext_noop("Sets lower threshold for an array length to apply"
+ " constants merging when computing query identifier."),
+ gettext_noop("Not used if query_id_const_merge is disabled"),
+ },
+ &query_id_const_merge_threshold,
+ 1, 1, INT_MAX,
+ NULL, NULL, NULL
+ },
+
/* End-of-list marker */
{
{NULL, 0, 0, NULL, NULL}, NULL, 0, 0, 0, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 3397780dc72..6cc30e116c4 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -629,6 +629,7 @@
#log_planner_stats = off
#log_executor_stats = off
#query_id_const_merge = off
+#query_id_const_merge_threshold = 1
#------------------------------------------------------------------------------
# AUTOVACUUM
diff --git a/src/include/nodes/queryjumble.h b/src/include/nodes/queryjumble.h
index cfa99efc14e..8f823c3c491 100644
--- a/src/include/nodes/queryjumble.h
+++ b/src/include/nodes/queryjumble.h
@@ -72,6 +72,7 @@ enum ComputeQueryIdType
/* GUC parameters */
extern PGDLLIMPORT int compute_query_id;
extern PGDLLIMPORT bool query_id_const_merge;
+extern PGDLLIMPORT bool query_id_const_merge_threshold;
extern const char *CleanQuerytext(const char *query, int *location, int *len);
extern JumbleState *JumbleQuery(Query *query);
--
2.41.0