Subject: [PATCH v15 1/4] Prevent jumbling of every element in ArrayExpr

From: Dmitrii Dolgov <[email-masked]>
Date: Sat, 14 Oct 2023 15:00:48 +0200

pg_stat_statements produces multiple entries for queries like

    SELECT something FROM table WHERE col IN (1, 2, 3, ...)

depending on the number of parameters, because every element of
ArrayExpr is jumbled. In certain situations it's undesirable, especially
if the list becomes too large.

Make an array of Const expressions contribute only the first/last
elements to the jumble hash. Allow to enable this behavior via the new
GUC query_id_const_merge with the default value off.

Reviewed-by: Zhihong Yu, Sergey Dudoladov, Robert Haas, Tom Lane,
Michael Paquier, Sergei Kornilov, Alvaro Herrera, David Geier
Tested-by: Chengxi Sun
---
 contrib/pg_stat_statements/Makefile           |   2 +-
 .../pg_stat_statements/expected/merging.out   | 167 ++++++++++++++++++
 contrib/pg_stat_statements/meson.build        |   1 +
 .../pg_stat_statements/pg_stat_statements.c   |  34 +++-
 contrib/pg_stat_statements/sql/merging.sql    |  58 ++++++
 doc/src/sgml/config.sgml                      |  28 +++
 doc/src/sgml/pgstatstatements.sgml            |  25 ++-
 src/backend/nodes/gen_node_support.pl         |   2 +-
 src/backend/nodes/queryjumblefuncs.c          |  86 ++++++++-
 src/backend/utils/misc/guc_tables.c           |  10 ++
 src/backend/utils/misc/postgresql.conf.sample |   2 +-
 src/include/nodes/primnodes.h                 |   2 +
 src/include/nodes/queryjumble.h               |   9 +-
 13 files changed, 406 insertions(+), 20 deletions(-)
 create mode 100644 contrib/pg_stat_statements/expected/merging.out
 create mode 100644 contrib/pg_stat_statements/sql/merging.sql

diff --git a/contrib/pg_stat_statements/Makefile b/contrib/pg_stat_statements/Makefile
index eba4a95d91a..af731fc9a58 100644
--- a/contrib/pg_stat_statements/Makefile
+++ b/contrib/pg_stat_statements/Makefile
@@ -19,7 +19,7 @@ LDFLAGS_SL += $(filter -lm, $(LIBS))
 
 REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/pg_stat_statements/pg_stat_statements.conf
 REGRESS = select dml cursors utility level_tracking planning \
-	user_activity wal cleanup oldextversions
+	user_activity wal cleanup oldextversions merging
 # Disabled because these tests require "shared_preload_libraries=pg_stat_statements",
 # which typical installcheck users do not have (e.g. buildfarm clients).
 NO_INSTALLCHECK = 1
diff --git a/contrib/pg_stat_statements/expected/merging.out b/contrib/pg_stat_statements/expected/merging.out
new file mode 100644
index 00000000000..7711572e0b7
--- /dev/null
+++ b/contrib/pg_stat_statements/expected/merging.out
@@ -0,0 +1,167 @@
+--
+-- Const merging functionality
+--
+CREATE EXTENSION pg_stat_statements;
+CREATE TABLE test_merge (id int, data int);
+-- IN queries
+-- No merging is performed, as a baseline result
+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 ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)      |     1
+ SELECT * FROM test_merge WHERE id IN ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11) |     1
+ SELECT pg_stat_statements_reset()                                                   |     1
+(4 rows)
+
+-- Normal scenario, too many simple constants for an IN query
+SET query_id_const_merge = on;
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+SELECT * FROM test_merge WHERE id IN (1);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3);
+ 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)  |     1
+ SELECT * FROM test_merge WHERE id IN (...) |     1
+ SELECT pg_stat_statements_reset()          |     1
+(3 rows)
+
+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)                              |     1
+ SELECT * FROM test_merge WHERE id IN (...)                             |     4
+ SELECT pg_stat_statements_reset()                                      |     1
+ SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C" |     1
+(4 rows)
+
+-- More conditions in the query
+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) and data = 2;
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) and data = 2;
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) and data = 2;
+ 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 (...) and data = $3 |     3
+ SELECT pg_stat_statements_reset()                        |     1
+(2 rows)
+
+-- No constants simplification
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+SELECT * FROM test_merge WHERE id IN (1 + 1, 2 + 2, 3 + 3, 4 + 4, 5 + 5, 6 + 6, 7 + 7, 8 + 8, 9 + 9);
+ 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 + $10, $11 + $12, $13 + $14, $15 + $16, $17 + $18) |     1
+ SELECT pg_stat_statements_reset()                                                                                               |     1
+(2 rows)
+
+-- Numeric type
+CREATE TABLE test_merge_numeric (id int, data numeric(5, 2));
+SELECT pg_stat_statements_reset();
+ pg_stat_statements_reset 
+--------------------------
+ 
+(1 row)
+
+SELECT * FROM test_merge_numeric 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_numeric WHERE id IN (...) |     1
+ SELECT pg_stat_statements_reset()                  |     1
+(2 rows)
+
+-- Test constants evaluation, verifies a tricky part to make sure there are no
+-- issues in the merging implementation
+WITH cte AS (
+    SELECT 'const' as const FROM test_merge
+)
+SELECT ARRAY['a', 'b', 'c', const::varchar] AS result
+FROM cte;
+ result 
+--------
+(0 rows)
+
+RESET query_id_const_merge;
diff --git a/contrib/pg_stat_statements/meson.build b/contrib/pg_stat_statements/meson.build
index 15b7c7f2b02..6371c81e138 100644
--- a/contrib/pg_stat_statements/meson.build
+++ b/contrib/pg_stat_statements/meson.build
@@ -51,6 +51,7 @@ tests += {
       'wal',
       'cleanup',
       'oldextversions',
+      'merging',
     ],
     'regress_args': ['--temp-config', files('pg_stat_statements.conf')],
     # Disabled because these tests require
diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index a46f2db352b..0b03009a053 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -2695,6 +2695,9 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 				n_quer_loc = 0, /* Normalized query byte location */
 				last_off = 0,	/* Offset from start for previous tok */
 				last_tok_len = 0;	/* Length (in bytes) of that tok */
+	bool		skip = false; 	/* Signals that certain constants are
+								   merged together and have to be skipped */
+
 
 	/*
 	 * Get constants' lengths (core system only gives us locations).  Note
@@ -2718,7 +2721,6 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 	{
 		int			off,		/* Offset from start for cur tok */
 					tok_len;	/* Length (in bytes) of that tok */
-
 		off = jstate->clocations[i].location;
 		/* Adjust recorded location if we're dealing with partial string */
 		off -= query_loc;
@@ -2733,12 +2735,32 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 		len_to_wrt -= last_tok_len;
 
 		Assert(len_to_wrt >= 0);
-		memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
-		n_quer_loc += len_to_wrt;
 
-		/* And insert a param symbol in place of the constant token */
-		n_quer_loc += sprintf(norm_query + n_quer_loc, "$%d",
-							  i + 1 + jstate->highest_extern_param_id);
+		/* Normal path, non merged constant */
+		if (!jstate->clocations[i].merged)
+		{
+			memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
+			n_quer_loc += len_to_wrt;
+
+			/* And insert a param symbol in place of the constant token */
+			n_quer_loc += sprintf(norm_query + n_quer_loc, "$%d",
+								  i + 1 + jstate->highest_extern_param_id);
+
+			/* In case previous constants were merged away, stop doing that */
+			if (skip)
+				skip = false;
+		}
+		/* The firsts merged constant */
+		else if (!skip)
+		{
+			memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
+			n_quer_loc += len_to_wrt;
+
+			/* Skip the following until a non merged constant appear */
+			skip = true;
+			n_quer_loc += sprintf(norm_query + n_quer_loc, "...");
+		}
+		/* Otherwise the constant is merged away */
 
 		quer_loc = off + tok_len;
 		last_off = off;
diff --git a/contrib/pg_stat_statements/sql/merging.sql b/contrib/pg_stat_statements/sql/merging.sql
new file mode 100644
index 00000000000..02266a92ce8
--- /dev/null
+++ b/contrib/pg_stat_statements/sql/merging.sql
@@ -0,0 +1,58 @@
+--
+-- Const merging functionality
+--
+CREATE EXTENSION pg_stat_statements;
+
+CREATE TABLE test_merge (id int, data int);
+
+-- IN queries
+
+-- No merging is performed, as a baseline result
+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";
+
+-- Normal scenario, too many simple constants for an IN query
+SET query_id_const_merge = on;
+
+SELECT pg_stat_statements_reset();
+SELECT * FROM test_merge WHERE id IN (1);
+SELECT * FROM test_merge WHERE id IN (1, 2, 3);
+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);
+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";
+
+-- More conditions in the query
+SELECT pg_stat_statements_reset();
+
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9) and data = 2;
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) and data = 2;
+SELECT * FROM test_merge WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11) and data = 2;
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- No constants simplification
+SELECT pg_stat_statements_reset();
+
+SELECT * FROM test_merge WHERE id IN (1 + 1, 2 + 2, 3 + 3, 4 + 4, 5 + 5, 6 + 6, 7 + 7, 8 + 8, 9 + 9);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Numeric type
+CREATE TABLE test_merge_numeric (id int, data numeric(5, 2));
+SELECT pg_stat_statements_reset();
+SELECT * FROM test_merge_numeric 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";
+
+-- Test constants evaluation, verifies a tricky part to make sure there are no
+-- issues in the merging implementation
+WITH cte AS (
+    SELECT 'const' as const FROM test_merge
+)
+SELECT ARRAY['a', 'b', 'c', const::varchar] AS result
+FROM cte;
+
+RESET query_id_const_merge;
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3839c72c868..55b0795bce1 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8190,6 +8190,34 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-query-id-const-merge" xreflabel="query_id_const_merge">
+      <term><varname>query_id_const_merge</varname> (<type>bool</type>)
+      <indexterm>
+       <primary><varname>query_id_const_merge</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies how an array of constants (e.g. for an "IN" clause)
+        contributes to the query identifier computation. Normally every element
+        of an array contributes to the query identifier, which means the same
+        query will get multiple different identifiers, one for each occurrence
+        with an array of different lenght.
+
+        If this parameter is on, an array of constants will contribute only the
+        first and the last elements to the query identifier. It means two
+        occurences of the same query, where the only difference is number of
+        constants in the array, are going to get the same query identifier.
+
+        The parameter could be used to reduce amount of repeating data stored
+        via <xref linkend="pgstatstatements"/> extension.  The default value is off.
+
+        The <xref linkend="pgstatstatements"/> extension will represent such
+        queries in form <literal>'(...)'</literal>.
+       </para>
+      </listitem>
+     </varlistentry>
+
      </variablelist>
 
     </sect2>
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index 7e7c5c9ff82..8df4064cbf4 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -548,10 +548,27 @@
   <para>
    In some cases, queries with visibly different texts might get merged into a
    single <structname>pg_stat_statements</structname> entry.  Normally this will happen
-   only for semantically equivalent queries, 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.)
+   only for semantically equivalent queries, or if
+   <xref linkend="guc-query-id-const-merge"/> is enabled and the only
+   difference between queries is the length of an array with constants they contain:
+
+<screen>
+=# SET query_id_const_merge = on;
+=# SELECT pg_stat_statements_reset();
+=# SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+=# SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12);
+=# SELECT query, calls FROM pg_stat_statements;
+-[ RECORD 1 ]------------------------------
+query | SELECT * FROM test WHERE a IN (...)
+calls | 2
+-[ RECORD 2 ]------------------------------
+query | SELECT pg_stat_statements_reset()
+calls | 1
+</screen>
+
+   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.)
   </para>
 
   <para>
diff --git a/src/backend/nodes/gen_node_support.pl b/src/backend/nodes/gen_node_support.pl
index 72c79635781..5b4a3f37a2b 100644
--- a/src/backend/nodes/gen_node_support.pl
+++ b/src/backend/nodes/gen_node_support.pl
@@ -1308,7 +1308,7 @@ _jumble${n}(JumbleState *jstate, Node *node)
 			# Track the node's location only if directly requested.
 			if ($query_jumble_location)
 			{
-				print $jff "\tJUMBLE_LOCATION($f);\n"
+				print $jff "\tJUMBLE_LOCATION($f, false);\n"
 				  unless $query_jumble_ignore;
 			}
 		}
diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
index 281907a4d83..52d45c2b093 100644
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -42,12 +42,16 @@
 /* GUC parameters */
 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;
+
 /* True when compute_query_id is ON, or AUTO and a module requests them */
 bool		query_id_enabled = false;
 
 static void AppendJumble(JumbleState *jstate,
 						 const unsigned char *item, Size size);
-static void RecordConstLocation(JumbleState *jstate, int location);
+static void RecordConstLocation(JumbleState *jstate,
+								int location, bool merged);
 static void _jumbleNode(JumbleState *jstate, Node *node);
 static void _jumbleA_Const(JumbleState *jstate, Node *node);
 static void _jumbleList(JumbleState *jstate, Node *node);
@@ -186,11 +190,15 @@ AppendJumble(JumbleState *jstate, const unsigned char *item, Size size)
 }
 
 /*
- * Record location of constant within query string of query tree
- * that is currently being walked.
+ * Record location of constant within query string of query tree that is
+ * currently being walked.
+ *
+ * Merged argument signals that the constant represents the first or the last
+ * element in a series of merged constants, and everything but the first/last
+ * element contributes nothing to the jumble hash.
  */
 static void
-RecordConstLocation(JumbleState *jstate, int location)
+RecordConstLocation(JumbleState *jstate, int location, bool merged)
 {
 	/* -1 indicates unknown or undefined location */
 	if (location >= 0)
@@ -206,15 +214,65 @@ RecordConstLocation(JumbleState *jstate, int location)
 		}
 		jstate->clocations[jstate->clocations_count].location = location;
 		/* initialize lengths to -1 to simplify third-party module usage */
+		jstate->clocations[jstate->clocations_count].merged = merged;
 		jstate->clocations[jstate->clocations_count].length = -1;
 		jstate->clocations_count++;
 	}
 }
 
+/*
+ * Verify if the provided list contains could be merged down, which means it
+ * contains only constant expressions.
+ *
+ * Return value indicates if merging is possible.
+ *
+ * Note that this function searches only for explicit Const nodes and does not
+ * try to simplify expressions.
+ */
+static bool
+IsMergeableConstList(List *elements, Const **firstConst, Const **lastConst)
+{
+	ListCell   *temp;
+	Node	   *firstExpr = NULL;
+
+	if (elements == NULL)
+		return false;
+
+	if (!query_id_const_merge)
+	{
+		/* Merging is disabled, process everything one by one */
+		return false;
+	}
+
+	firstExpr = linitial(elements);
+
+	/*
+	 * If the first expression is a constant, verify if the following elements
+	 * are constants as well. If yes, the list is eligible for merging, and the
+	 * order of magnitude need to be calculated.
+	 */
+	if (IsA(firstExpr, Const))
+	{
+		foreach(temp, elements)
+			if (!IsA(lfirst(temp), Const))
+				return false;
+
+		*firstConst = (Const *) firstExpr;
+		*lastConst = llast_node(Const, elements);
+		return true;
+	}
+
+	/*
+	 * If we end up here, it means no constants merging is possible, process
+	 * the list as usual.
+	 */
+	return false;
+}
+
 #define JUMBLE_NODE(item) \
 	_jumbleNode(jstate, (Node *) expr->item)
-#define JUMBLE_LOCATION(location) \
-	RecordConstLocation(jstate, expr->location)
+#define JUMBLE_LOCATION(location, merged) \
+	RecordConstLocation(jstate, expr->location, merged)
 #define JUMBLE_FIELD(item) \
 	AppendJumble(jstate, (const unsigned char *) &(expr->item), sizeof(expr->item))
 #define JUMBLE_FIELD_SINGLE(item) \
@@ -227,6 +285,22 @@ do { \
 
 #include "queryjumblefuncs.funcs.c"
 
+static void
+_jumbleArrayExpr(JumbleState *jstate, Node *node)
+{
+	ArrayExpr *expr = (ArrayExpr *) node;
+	Const *first, *last;
+	if(IsMergeableConstList(expr->elements, &first, &last))
+	{
+		RecordConstLocation(jstate, first->location, true);
+		RecordConstLocation(jstate, last->location, true);
+	}
+	else
+	{
+		JUMBLE_NODE(elements);
+	}
+}
+
 static void
 _jumbleNode(JumbleState *jstate, Node *node)
 {
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 4c585741661..fbb50adb9f9 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2011,6 +2011,16 @@ struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"query_id_const_merge", PGC_SUSET, STATS_MONITORING,
+			gettext_noop("Sets whether an array of constants will contribute to"
+						 " query identified computation."),
+		},
+		&query_id_const_merge,
+		false,
+		NULL, NULL, NULL
+	},
+
 	/* End-of-list marker */
 	{
 		{NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index d08d55c3fe4..3397780dc72 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -628,7 +628,7 @@
 #log_parser_stats = off
 #log_planner_stats = off
 #log_executor_stats = off
-
+#query_id_const_merge = off
 
 #------------------------------------------------------------------------------
 # AUTOVACUUM
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index 60d72a876b4..fde0320b263 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1296,6 +1296,8 @@ typedef struct CaseTestExpr
  */
 typedef struct ArrayExpr
 {
+	pg_node_attr(custom_query_jumble)
+
 	Expr		xpr;
 	/* type of expression result */
 	Oid			array_typeid pg_node_attr(query_jumble_ignore);
diff --git a/src/include/nodes/queryjumble.h b/src/include/nodes/queryjumble.h
index 7649e095aa5..225957d7b3c 100644
--- a/src/include/nodes/queryjumble.h
+++ b/src/include/nodes/queryjumble.h
@@ -15,6 +15,7 @@
 #define QUERYJUMBLE_H
 
 #include "nodes/parsenodes.h"
+#include "nodes/nodeFuncs.h"
 
 /*
  * Struct for tracking locations/lengths of constants during normalization
@@ -23,6 +24,12 @@ typedef struct LocationLen
 {
 	int			location;		/* start offset in query text */
 	int			length;			/* length in bytes, or -1 to ignore */
+
+	/*
+	 * Indicates the constant represents the beginning or the end of a merged
+	 * constants interval.
+	 */
+	bool		merged;
 } LocationLen;
 
 /*
@@ -61,7 +68,7 @@ enum ComputeQueryIdType
 
 /* GUC parameters */
 extern PGDLLIMPORT int compute_query_id;
-
+extern PGDLLIMPORT bool query_id_const_merge;
 
 extern const char *CleanQuerytext(const char *query, int *location, int *len);
 extern JumbleState *JumbleQuery(Query *query);

base-commit: 22655aa23132a0645fdcdce4b233a1fff0c0cf8f
-- 
2.41.0

--svnhsmawrtczycxj
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
	filename="v15-0002-Reusable-decimalLength-functions.patch"