Subject: [PATCH v29] Prevent jumbling of every element in ArrayExpr

From: Dmitrii Dolgov <[email-masked]>
Date: Tue, 3 Dec 2024 14:55:45 +0100

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
pg_stat_statements parameter query_id_squash_values with the default value off.

Reviewed-by: Zhihong Yu, Sergey Dudoladov, Robert Haas, Tom Lane,
Michael Paquier, Sergei Kornilov, Alvaro Herrera, David Geier, Sutou Kouhei,
Sami Imseih, Julien Rouhaud
Tested-by: Chengxi Sun, Yasuo Honda
---
 contrib/pg_stat_statements/Makefile           |   2 +-
 .../pg_stat_statements/expected/squashing.out | 465 ++++++++++++++++++
 contrib/pg_stat_statements/meson.build        |   1 +
 .../pg_stat_statements/pg_stat_statements.c   |  76 ++-
 contrib/pg_stat_statements/sql/squashing.sql  | 180 +++++++
 doc/src/sgml/config.sgml                      |  29 ++
 doc/src/sgml/pgstatstatements.sgml            |  26 +-
 src/backend/nodes/gen_node_support.pl         |  19 +-
 src/backend/nodes/queryjumblefuncs.c          | 145 +++++-
 src/backend/postmaster/launch_backend.c       |   3 +
 src/backend/utils/misc/guc_tables.c           |  10 +
 src/backend/utils/misc/postgresql.conf.sample |   1 +
 src/include/nodes/nodes.h                     |   2 +
 src/include/nodes/primnodes.h                 |   2 +-
 src/include/nodes/queryjumble.h               |   7 +
 15 files changed, 945 insertions(+), 23 deletions(-)
 create mode 100644 contrib/pg_stat_statements/expected/squashing.out
 create mode 100644 contrib/pg_stat_statements/sql/squashing.sql

diff --git a/contrib/pg_stat_statements/Makefile b/contrib/pg_stat_statements/Makefile
index 241c02587bc..b2bd8794d2a 100644
--- a/contrib/pg_stat_statements/Makefile
+++ b/contrib/pg_stat_statements/Makefile
@@ -20,7 +20,7 @@ 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 entry_timestamp privileges extended \
-	parallel cleanup oldextversions
+	parallel cleanup oldextversions squashing
 # 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/squashing.out b/contrib/pg_stat_statements/expected/squashing.out
new file mode 100644
index 00000000000..f7bcba2388c
--- /dev/null
+++ b/contrib/pg_stat_statements/expected/squashing.out
@@ -0,0 +1,465 @@
+--
+-- Const squashing functionality
+--
+CREATE EXTENSION pg_stat_statements;
+CREATE TABLE test_squash (id int, data int);
+-- IN queries
+-- No squashing is performed, as a baseline result
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash 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_squash WHERE id IN ($1, $2, $3, $4, $5, $6, $7, $8, $9)           |     1
+ SELECT * FROM test_squash WHERE id IN ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10)      |     1
+ SELECT * FROM test_squash WHERE id IN ($1, $2, $3, $4, $5, $6, $7, $8, $9, $10, $11) |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                                   |     1
+(4 rows)
+
+-- Normal scenario, too many simple constants for an IN query
+SET query_id_squash_values = on;
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash WHERE id IN (1);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash 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_squash WHERE id IN ($1 /*, ... */) |     1
+ SELECT * FROM test_squash WHERE id IN ($1)            |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t    |     1
+(3 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash 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_squash WHERE id IN ($1 /*, ... */)                  |     4
+ SELECT * FROM test_squash WHERE id IN ($1)                             |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                     |     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() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9) AND data = 2;
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) AND data = 2;
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash 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_squash WHERE id IN ($1 /*, ... */) AND data = $2 |     3
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                  |     1
+(2 rows)
+
+-- Multiple squashed intervals
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9)
+    AND data IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+    AND data IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+ id | data 
+----+------
+(0 rows)
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
+    AND data 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_squash WHERE id IN ($1 /*, ... */)+|     3
+     AND data IN ($2 /*, ... */)                       | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t    |     1
+(2 rows)
+
+-- No constants simplification for OpExpr
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+-- In the following two queries the operator expressions (+) and (@) have
+-- different oppno, and will be given different query_id if squashed, even though
+-- the normalized query will be the same
+SELECT * FROM test_squash 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 * FROM test_squash WHERE id IN
+	(@ '-1', @ '-2', @ '-3', @ '-4', @ '-5', @ '-6', @ '-7', @ '-8', @ '-9');
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                                               query                                                | calls 
+----------------------------------------------------------------------------------------------------+-------
+ SELECT * FROM test_squash WHERE id IN                                                             +|     1
+         ($1 + $2, $3 + $4, $5 + $6, $7 + $8, $9 + $10, $11 + $12, $13 + $14, $15 + $16, $17 + $18) | 
+ SELECT * FROM test_squash WHERE id IN                                                             +|     1
+         (@ $1, @ $2, @ $3, @ $4, @ $5, @ $6, @ $7, @ $8, @ $9)                                     | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                                                 |     1
+(3 rows)
+
+-- FuncExpr
+-- Verify multiple type representation end up with the same query_id
+CREATE TABLE test_float (data float);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT data FROM test_float WHERE data IN (1, 2);
+ data 
+------
+(0 rows)
+
+SELECT data FROM test_float WHERE data IN (1, '2');
+ data 
+------
+(0 rows)
+
+SELECT data FROM test_float WHERE data IN ('1', 2);
+ data 
+------
+(0 rows)
+
+SELECT data FROM test_float WHERE data IN ('1', '2');
+ data 
+------
+(0 rows)
+
+SELECT data FROM test_float WHERE data IN (1.0, 1.0);
+ data 
+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                           query                           | calls 
+-----------------------------------------------------------+-------
+ SELECT data FROM test_float WHERE data IN ($1 /*, ... */) |     5
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t        |     1
+(2 rows)
+
+-- Numeric type, implicit cast is squashed
+CREATE TABLE test_squash_numeric (id int, data numeric(5, 2));
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_numeric WHERE data 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_squash_numeric WHERE data IN ($1 /*, ... */) |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t              |     1
+(2 rows)
+
+-- Bigint, implicit cast is squashed
+CREATE TABLE test_squash_bigint (id int, data bigint);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_bigint WHERE data 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_squash_bigint WHERE data IN ($1 /*, ... */) |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t             |     1
+(2 rows)
+
+-- Bigint, explicit cast is not squashed
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_bigint WHERE data IN
+	(1::bigint, 2::bigint, 3::bigint, 4::bigint, 5::bigint, 6::bigint,
+	 7::bigint, 8::bigint, 9::bigint, 10::bigint, 11::bigint);
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                                      query                                       | calls 
+----------------------------------------------------------------------------------+-------
+ SELECT * FROM test_squash_bigint WHERE data IN                                  +|     1
+         ($1::bigint, $2::bigint, $3::bigint, $4::bigint, $5::bigint, $6::bigint,+| 
+          $7::bigint, $8::bigint, $9::bigint, $10::bigint, $11::bigint)           | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                               |     1
+(2 rows)
+
+-- Bigint, long tokens with parenthesis
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_bigint WHERE id IN
+	(abs(100), abs(200), abs(300), abs(400), abs(500), abs(600), abs(700),
+	 abs(800), abs(900), abs(1000), ((abs(1100))));
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                                  query                                  | calls 
+-------------------------------------------------------------------------+-------
+ SELECT * FROM test_squash_bigint WHERE id IN                           +|     1
+         (abs($1), abs($2), abs($3), abs($4), abs($5), abs($6), abs($7),+| 
+          abs($8), abs($9), abs($10), ((abs($11))))                      | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                      |     1
+(2 rows)
+
+-- CoerceViaIO, SubLink instead of a Const
+CREATE TABLE test_squash_jsonb (id int, data jsonb);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_jsonb WHERE data IN
+	((SELECT '"1"')::jsonb, (SELECT '"2"')::jsonb, (SELECT '"3"')::jsonb,
+	 (SELECT '"4"')::jsonb, (SELECT '"5"')::jsonb, (SELECT '"6"')::jsonb,
+	 (SELECT '"7"')::jsonb, (SELECT '"8"')::jsonb, (SELECT '"9"')::jsonb,
+	 (SELECT '"10"')::jsonb);
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                                query                                 | calls 
+----------------------------------------------------------------------+-------
+ SELECT * FROM test_squash_jsonb WHERE data IN                       +|     1
+         ((SELECT $1)::jsonb, (SELECT $2)::jsonb, (SELECT $3)::jsonb,+| 
+          (SELECT $4)::jsonb, (SELECT $5)::jsonb, (SELECT $6)::jsonb,+| 
+          (SELECT $7)::jsonb, (SELECT $8)::jsonb, (SELECT $9)::jsonb,+| 
+          (SELECT $10)::jsonb)                                        | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                   |     1
+(2 rows)
+
+-- CoerceViaIO
+-- Create some dummy type to force CoerceViaIO
+CREATE TYPE casttesttype;
+CREATE FUNCTION casttesttype_in(cstring)
+   RETURNS casttesttype
+   AS 'textin'
+   LANGUAGE internal STRICT IMMUTABLE;
+NOTICE:  return type casttesttype is only a shell
+CREATE FUNCTION casttesttype_out(casttesttype)
+   RETURNS cstring
+   AS 'textout'
+   LANGUAGE internal STRICT IMMUTABLE;
+NOTICE:  argument type casttesttype is only a shell
+LINE 1: CREATE FUNCTION casttesttype_out(casttesttype)
+                                         ^
+CREATE TYPE casttesttype (
+   internallength = variable,
+   input = casttesttype_in,
+   output = casttesttype_out,
+   alignment = int4
+);
+CREATE CAST (int4 AS casttesttype) WITH INOUT;
+CREATE FUNCTION casttesttype_eq(casttesttype, casttesttype)
+returns boolean language sql immutable as $$
+    SELECT true
+$$;
+CREATE OPERATOR = (
+    leftarg = casttesttype,
+    rightarg = casttesttype,
+    procedure = casttesttype_eq,
+    commutator = =);
+CREATE TABLE test_squash_cast (id int, data casttesttype);
+-- Use the introduced type to construct a list of CoerceViaIO around Const
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_cast WHERE data IN
+	(1::int4::casttesttype, 2::int4::casttesttype, 3::int4::casttesttype,
+	 4::int4::casttesttype, 5::int4::casttesttype, 6::int4::casttesttype,
+	 7::int4::casttesttype, 8::int4::casttesttype, 9::int4::casttesttype,
+	 10::int4::casttesttype, 11::int4::casttesttype);
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                       query                        | calls 
+----------------------------------------------------+-------
+ SELECT * FROM test_squash_cast WHERE data IN      +|     1
+         ($1 /*, ... */::int4::casttesttype)        | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t |     1
+(2 rows)
+
+-- Some casting expression are simplified to Const
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash_jsonb WHERE data IN
+	(('"1"')::jsonb, ('"2"')::jsonb, ('"3"')::jsonb, ('"4"')::jsonb,
+	 ( '"5"')::jsonb, ( '"6"')::jsonb, ( '"7"')::jsonb, ( '"8"')::jsonb,
+	 ( '"9"')::jsonb, ( '"10"')::jsonb);
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                       query                        | calls 
+----------------------------------------------------+-------
+ SELECT * FROM test_squash_jsonb WHERE data IN     +|     1
+         (($1 /*, ... */)::jsonb)                   | 
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t |     1
+(2 rows)
+
+-- RelabelType
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT * FROM test_squash WHERE id IN (1::oid, 2::oid, 3::oid, 4::oid, 5::oid, 6::oid, 7::oid, 8::oid, 9::oid);
+ id | data 
+----+------
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                           query                            | calls 
+------------------------------------------------------------+-------
+ SELECT * FROM test_squash WHERE id IN ($1 /*, ... */::oid) |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t         |     1
+(2 rows)
+
+-- Test constants evaluation in a CTE, which was causing issues in the past
+WITH cte AS (
+    SELECT 'const' as const FROM test_squash
+)
+SELECT ARRAY['a', 'b', 'c', const::varchar] AS result
+FROM cte;
+ result 
+--------
+(0 rows)
+
+-- Simple array would be squashed as well
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT ARRAY[1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+         array          
+------------------------
+ {1,2,3,4,5,6,7,8,9,10}
+(1 row)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                       query                        | calls 
+----------------------------------------------------+-------
+ SELECT ARRAY[$1 /*, ... */]                        |     1
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t |     1
+(2 rows)
+
+RESET query_id_squash_values;
diff --git a/contrib/pg_stat_statements/meson.build b/contrib/pg_stat_statements/meson.build
index 4446af58c58..01a6cbdcf61 100644
--- a/contrib/pg_stat_statements/meson.build
+++ b/contrib/pg_stat_statements/meson.build
@@ -56,6 +56,7 @@ tests += {
       'parallel',
       'cleanup',
       'oldextversions',
+      'squashing',
     ],
     '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 b245d04097d..8ab9ad58e1c 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -296,7 +296,6 @@ static bool pgss_track_planning = false;	/* whether to track planning
 											 * duration */
 static bool pgss_save = true;	/* whether to save stats across shutdown */
 
-
 #define pgss_enabled(level) \
 	(!IsParallelWorker() && \
 	(pgss_track == PGSS_TRACK_ALL || \
@@ -2823,6 +2822,10 @@ 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		in_squashed = false;	/* in a run of squashed consts? */
+	int			skipped_constants = 0;	/* Position adjustment of later
+										 * constants after squashed ones */
+
 
 	/*
 	 * Get constants' lengths (core system only gives us locations).  Note
@@ -2836,6 +2839,9 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 	 * certainly isn't more than 11 bytes, even if n reaches INT_MAX.  We
 	 * could refine that limit based on the max value of n for the current
 	 * query, but it hardly seems worth any extra effort to do so.
+	 *
+	 * Note this also gives enough room for the commented-out ", ..." list
+	 * syntax used by constant squashing.
 	 */
 	norm_query_buflen = query_len + jstate->clocations_count * 10;
 
@@ -2848,6 +2854,7 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 					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;
 
@@ -2856,18 +2863,67 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 		if (tok_len < 0)
 			continue;			/* ignore any duplicates */
 
-		/* Copy next chunk (what precedes the next constant) */
-		len_to_wrt = off - last_off;
-		len_to_wrt -= last_tok_len;
+		/*
+		 * What to do next depends on whether we're squashing constant lists,
+		 * and whether we're already in a run of such constants.
+		 */
+		if (!jstate->clocations[i].squashed)
+		{
+			/*
+			 * This location corresponds to a constant not to be squashed.
+			 * Print what comes before the constant ...
+			 */
+			len_to_wrt = off - last_off;
+			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;
+			Assert(len_to_wrt >= 0);
 
-		/* 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);
+			memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
+			n_quer_loc += len_to_wrt;
 
+			/* ... and then a param symbol replacing the constant itself */
+			n_quer_loc += sprintf(norm_query + n_quer_loc, "$%d",
+								  i + 1 + jstate->highest_extern_param_id - skipped_constants);
+
+			/* In case previous constants were merged away, stop doing that */
+			in_squashed = false;
+		}
+		else if (!in_squashed)
+		{
+			/*
+			 * This location is the start position of a run of constants to be
+			 * squashed, so we need to print the representation of starting a
+			 * group of stashed constants.
+			 *
+			 * Print what comes before the constant ...
+			 */
+			len_to_wrt = off - last_off;
+			len_to_wrt -= last_tok_len;
+			Assert(len_to_wrt >= 0);
+			Assert(i + 1 < jstate->clocations_count);
+			Assert(jstate->clocations[i + 1].squashed);
+			memcpy(norm_query + n_quer_loc, query + quer_loc, len_to_wrt);
+			n_quer_loc += len_to_wrt;
+
+			/* ... and then start a run of squashed constants */
+			n_quer_loc += sprintf(norm_query + n_quer_loc, "$%d /*, ... */",
+								  i + 1 + jstate->highest_extern_param_id - skipped_constants);
+
+			/* The next location will match the block below, to end the run */
+			in_squashed = true;
+
+			skipped_constants++;
+		}
+		else
+		{
+			/*
+			 * The second location of a run of squashable elements; this
+			 * indicates its end.
+			 */
+			in_squashed = false;
+		}
+
+		/* Otherwise the constant is squashed away -- move forward */
 		quer_loc = off + tok_len;
 		last_off = off;
 		last_tok_len = tok_len;
diff --git a/contrib/pg_stat_statements/sql/squashing.sql b/contrib/pg_stat_statements/sql/squashing.sql
new file mode 100644
index 00000000000..56ee8ccb9a1
--- /dev/null
+++ b/contrib/pg_stat_statements/sql/squashing.sql
@@ -0,0 +1,180 @@
+--
+-- Const squashing functionality
+--
+CREATE EXTENSION pg_stat_statements;
+
+CREATE TABLE test_squash (id int, data int);
+
+-- IN queries
+
+-- No squashing is performed, as a baseline result
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+SELECT * FROM test_squash 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_squash_values = on;
+
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash WHERE id IN (1);
+SELECT * FROM test_squash WHERE id IN (1, 2, 3);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+SELECT * FROM test_squash 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() IS NOT NULL AS t;
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9) AND data = 2;
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) AND data = 2;
+SELECT * FROM test_squash 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";
+
+-- Multiple squashed intervals
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9)
+    AND data IN (1, 2, 3, 4, 5, 6, 7, 8, 9);
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10)
+    AND data IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+SELECT * FROM test_squash WHERE id IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
+    AND data IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- No constants simplification for OpExpr
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+
+-- In the following two queries the operator expressions (+) and (@) have
+-- different oppno, and will be given different query_id if squashed, even though
+-- the normalized query will be the same
+SELECT * FROM test_squash WHERE id IN
+	(1 + 1, 2 + 2, 3 + 3, 4 + 4, 5 + 5, 6 + 6, 7 + 7, 8 + 8, 9 + 9);
+SELECT * FROM test_squash WHERE id IN
+	(@ '-1', @ '-2', @ '-3', @ '-4', @ '-5', @ '-6', @ '-7', @ '-8', @ '-9');
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- FuncExpr
+
+-- Verify multiple type representation end up with the same query_id
+CREATE TABLE test_float (data float);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT data FROM test_float WHERE data IN (1, 2);
+SELECT data FROM test_float WHERE data IN (1, '2');
+SELECT data FROM test_float WHERE data IN ('1', 2);
+SELECT data FROM test_float WHERE data IN ('1', '2');
+SELECT data FROM test_float WHERE data IN (1.0, 1.0);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Numeric type, implicit cast is squashed
+CREATE TABLE test_squash_numeric (id int, data numeric(5, 2));
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_numeric WHERE data IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Bigint, implicit cast is squashed
+CREATE TABLE test_squash_bigint (id int, data bigint);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_bigint WHERE data IN (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Bigint, explicit cast is not squashed
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_bigint WHERE data IN
+	(1::bigint, 2::bigint, 3::bigint, 4::bigint, 5::bigint, 6::bigint,
+	 7::bigint, 8::bigint, 9::bigint, 10::bigint, 11::bigint);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Bigint, long tokens with parenthesis
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_bigint WHERE id IN
+	(abs(100), abs(200), abs(300), abs(400), abs(500), abs(600), abs(700),
+	 abs(800), abs(900), abs(1000), ((abs(1100))));
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- CoerceViaIO, SubLink instead of a Const
+CREATE TABLE test_squash_jsonb (id int, data jsonb);
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_jsonb WHERE data IN
+	((SELECT '"1"')::jsonb, (SELECT '"2"')::jsonb, (SELECT '"3"')::jsonb,
+	 (SELECT '"4"')::jsonb, (SELECT '"5"')::jsonb, (SELECT '"6"')::jsonb,
+	 (SELECT '"7"')::jsonb, (SELECT '"8"')::jsonb, (SELECT '"9"')::jsonb,
+	 (SELECT '"10"')::jsonb);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- CoerceViaIO
+
+-- Create some dummy type to force CoerceViaIO
+CREATE TYPE casttesttype;
+
+CREATE FUNCTION casttesttype_in(cstring)
+   RETURNS casttesttype
+   AS 'textin'
+   LANGUAGE internal STRICT IMMUTABLE;
+
+CREATE FUNCTION casttesttype_out(casttesttype)
+   RETURNS cstring
+   AS 'textout'
+   LANGUAGE internal STRICT IMMUTABLE;
+
+CREATE TYPE casttesttype (
+   internallength = variable,
+   input = casttesttype_in,
+   output = casttesttype_out,
+   alignment = int4
+);
+
+CREATE CAST (int4 AS casttesttype) WITH INOUT;
+
+CREATE FUNCTION casttesttype_eq(casttesttype, casttesttype)
+returns boolean language sql immutable as $$
+    SELECT true
+$$;
+
+CREATE OPERATOR = (
+    leftarg = casttesttype,
+    rightarg = casttesttype,
+    procedure = casttesttype_eq,
+    commutator = =);
+
+CREATE TABLE test_squash_cast (id int, data casttesttype);
+
+-- Use the introduced type to construct a list of CoerceViaIO around Const
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_cast WHERE data IN
+	(1::int4::casttesttype, 2::int4::casttesttype, 3::int4::casttesttype,
+	 4::int4::casttesttype, 5::int4::casttesttype, 6::int4::casttesttype,
+	 7::int4::casttesttype, 8::int4::casttesttype, 9::int4::casttesttype,
+	 10::int4::casttesttype, 11::int4::casttesttype);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Some casting expression are simplified to Const
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash_jsonb WHERE data IN
+	(('"1"')::jsonb, ('"2"')::jsonb, ('"3"')::jsonb, ('"4"')::jsonb,
+	 ( '"5"')::jsonb, ( '"6"')::jsonb, ( '"7"')::jsonb, ( '"8"')::jsonb,
+	 ( '"9"')::jsonb, ( '"10"')::jsonb);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- RelabelType
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT * FROM test_squash WHERE id IN (1::oid, 2::oid, 3::oid, 4::oid, 5::oid, 6::oid, 7::oid, 8::oid, 9::oid);
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+-- Test constants evaluation in a CTE, which was causing issues in the past
+WITH cte AS (
+    SELECT 'const' as const FROM test_squash
+)
+SELECT ARRAY['a', 'b', 'c', const::varchar] AS result
+FROM cte;
+
+-- Simple array would be squashed as well
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT ARRAY[1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
+RESET query_id_squash_values;
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 3d62c8bd274..3140d922e0b 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -8626,6 +8626,35 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
       </listitem>
      </varlistentry>
 
+     <varlistentry id="guc-query-id-squash-values" xreflabel="query_id_squash_values">
+      <term><varname>query_id_squash_values</varname> (<type>bool</type>)
+      <indexterm>
+       <primary><varname>query_id_squash_values</varname> configuration parameter</primary>
+      </indexterm>
+      </term>
+      <listitem>
+       <para>
+        Specifies how a list of constants (e.g., for an <literal>IN</literal>
+        clause) contributes to the query identifier computation.
+        Normally, every element of such a list contributes to the query
+        identifier separately, which means that two queries that only differ
+        in the number of elements in such a list would get different query
+        identifiers.
+        If this parameter is on, a list of constants will not contribute
+        to the query identifier. This means that two queries whose only
+        difference is the number of constants in such a list are going to get the
+        same query identifier.
+       </para>
+       <para>
+        Only constants are affected; bind parameters do not benefit from this
+        functionality. The default value is <literal>off</literal>.
+       </para>
+       <para>
+        This parameter also affects how <xref linkend="pgstatstatements"/>
+        generates normalized query texts.
+      </listitem>
+     </varlistentry>
+
      <varlistentry id="guc-log-statement-stats">
       <term><varname>log_statement_stats</varname> (<type>boolean</type>)
       <indexterm>
diff --git a/doc/src/sgml/pgstatstatements.sgml b/doc/src/sgml/pgstatstatements.sgml
index e2ac1c2d501..c4e04cbb7f8 100644
--- a/doc/src/sgml/pgstatstatements.sgml
+++ b/doc/src/sgml/pgstatstatements.sgml
@@ -630,11 +630,29 @@
 
   <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.
+   single <structname>pg_stat_statements</structname> entry; as explained above,
+   this is expected to happen for semantically equivalent queries.
+   In addition, if <varname>query_id_squash_values</varname> is enabled
+   and the only difference between queries is the number of elements in a list
+   of constants, the list will get squashed down to a single element but shown
+   with a commented-out list indicator:
+
+<screen>
+=# SET query_id_squash_values = on;
+=# SELECT pg_stat_statements_reset();
+=# SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5, 6, 7);
+=# SELECT * FROM test WHERE a IN (1, 2, 3, 4, 5, 6, 7, 8);
+=# SELECT query, calls FROM pg_stat_statements
+   WHERE query LIKE 'SELECT%';
+-[ RECORD 1 ]------------------------------
+query | SELECT * FROM test WHERE a IN ($1 /*, ... */)
+calls | 2
+</screen>
+
+   In addition to these cases, 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.)
+    however.)
   </para>
 
   <para>
diff --git a/src/backend/nodes/gen_node_support.pl b/src/backend/nodes/gen_node_support.pl
index 1a657f7e0ae..7e3f335ac09 100644
--- a/src/backend/nodes/gen_node_support.pl
+++ b/src/backend/nodes/gen_node_support.pl
@@ -476,6 +476,7 @@ foreach my $infile (@ARGV)
 								equal_ignore_if_zero
 								query_jumble_ignore
 								query_jumble_location
+								query_jumble_squash
 								read_write_ignore
 								write_only_relids
 								write_only_nondefault_pathtarget
@@ -1283,6 +1284,7 @@ _jumble${n}(JumbleState *jstate, Node *node)
 		my @a = @{ $node_type_info{$n}->{field_attrs}{$f} };
 		my $query_jumble_ignore = $struct_no_query_jumble;
 		my $query_jumble_location = 0;
+		my $query_jumble_squash = 0;
 
 		# extract per-field attributes
 		foreach my $a (@a)
@@ -1295,14 +1297,27 @@ _jumble${n}(JumbleState *jstate, Node *node)
 			{
 				$query_jumble_location = 1;
 			}
+			elsif ($a eq 'query_jumble_squash')
+			{
+				$query_jumble_squash = 1;
+			}
 		}
 
 		# node type
 		if (($t =~ /^(\w+)\*$/ or $t =~ /^struct\s+(\w+)\*$/)
 			and elem $1, @node_types)
 		{
-			print $jff "\tJUMBLE_NODE($f);\n"
-			  unless $query_jumble_ignore;
+			# Squash constants if requested.
+			if ($query_jumble_squash)
+			{
+				print $jff "\tJUMBLE_ELEMENTS($f);\n"
+				  unless $query_jumble_ignore;
+			}
+			else
+			{
+				print $jff "\tJUMBLE_NODE($f);\n"
+				  unless $query_jumble_ignore;
+			}
 		}
 		elsif ($t eq 'ParseLoc')
 		{
diff --git a/src/backend/nodes/queryjumblefuncs.c b/src/backend/nodes/queryjumblefuncs.c
index b103a281936..b2394066404 100644
--- a/src/backend/nodes/queryjumblefuncs.c
+++ b/src/backend/nodes/queryjumblefuncs.c
@@ -32,9 +32,13 @@
  */
 #include "postgres.h"
 
+#include "access/transam.h"
+#include "catalog/pg_proc.h"
 #include "common/hashfn.h"
 #include "miscadmin.h"
+#include "nodes/nodeFuncs.h"
 #include "nodes/queryjumble.h"
+#include "utils/lsyscache.h"
 #include "parser/scansup.h"
 
 #define JUMBLE_SIZE				1024	/* query serialization buffer size */
@@ -42,6 +46,9 @@
 /* GUC parameters */
 int			compute_query_id = COMPUTE_QUERY_ID_AUTO;
 
+/* Whether to merge constants in a list when computing query_id */
+bool		query_id_squash_values = false;
+
 /*
  * True when compute_query_id is ON or AUTO, and a module requests them.
  *
@@ -53,8 +60,10 @@ 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 _jumbleElements(JumbleState *jstate, List *elements);
 static void _jumbleA_Const(JumbleState *jstate, Node *node);
 static void _jumbleList(JumbleState *jstate, Node *node);
 static void _jumbleVariableSetStmt(JumbleState *jstate, Node *node);
@@ -198,11 +207,15 @@ 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.
+ *
+ * 'squashed' 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 squashed)
 {
 	/* -1 indicates unknown or undefined location */
 	if (location >= 0)
@@ -218,15 +231,98 @@ 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].squashed = squashed;
 		jstate->clocations[jstate->clocations_count].length = -1;
 		jstate->clocations_count++;
 	}
 }
 
+/*
+ * Subroutine for _jumbleElements: Verify a few simple cases where we can
+ * deduce that the expression is a constant:
+ *
+ * - Ignore a possible wrapping RelabelType and CoerceViaIO.
+ * - If it's a FuncExpr, check that the function is an implicit
+ *   cast and its arguments are Const.
+ * - Otherwise test if the expression is a simple Const.
+ */
+static bool
+IsSquashableConst(Node *element)
+{
+	if (IsA(element, RelabelType))
+		element = (Node *) ((RelabelType *) element)->arg;
+
+	if (IsA(element, CoerceViaIO))
+		element = (Node *) ((CoerceViaIO *) element)->arg;
+
+	if (IsA(element, FuncExpr))
+	{
+		FuncExpr   *func = (FuncExpr *) element;
+		ListCell   *temp;
+
+		if (func->funcformat != COERCE_IMPLICIT_CAST)
+			return false;
+
+		if (func->funcid > FirstGenbkiObjectId)
+			return false;
+
+		foreach(temp, func->args)
+		{
+			Node	   *arg = lfirst(temp);
+
+			if (!IsA(arg, Const))	/* XXX we could recurse here instead */
+				return false;
+		}
+
+		return true;
+	}
+
+	if (!IsA(element, Const))
+		return false;
+
+	return true;
+}
+
+/*
+ * Subroutine for _jumbleElements: Verify whether the provided list
+ * can be squashed, meaning it contains only constant expressions.
+ *
+ * Return value indicates if squashing is possible.
+ *
+ * Note that this function searches only for explicit Const nodes with
+ * possibly very simple decorations on top, and does not try to simplify
+ * expressions.
+ */
+static bool
+IsSquashableConstList(List *elements, Node **firstExpr, Node **lastExpr)
+{
+	ListCell   *temp;
+
+	/*
+	 * If squashing is disabled, or the list is too short, we don't try to
+	 * squash it.
+	 */
+	if (!query_id_squash_values || list_length(elements) < 2)
+		return false;
+
+	foreach(temp, elements)
+	{
+		if (!IsSquashableConst(lfirst(temp)))
+			return false;
+	}
+
+	*firstExpr = linitial(elements);
+	*lastExpr = llast(elements);
+
+	return true;
+}
+
 #define JUMBLE_NODE(item) \
 	_jumbleNode(jstate, (Node *) expr->item)
+#define JUMBLE_ELEMENTS(list) \
+	_jumbleElements(jstate, (List *) expr->list)
 #define JUMBLE_LOCATION(location) \
-	RecordConstLocation(jstate, expr->location)
+	RecordConstLocation(jstate, expr->location, false)
 #define JUMBLE_FIELD(item) \
 	AppendJumble(jstate, (const unsigned char *) &(expr->item), sizeof(expr->item))
 #define JUMBLE_FIELD_SINGLE(item) \
@@ -239,6 +335,45 @@ do { \
 
 #include "queryjumblefuncs.funcs.c"
 
+/*
+ * When query_id_squash_values is enabled, we jumble lists of constant
+ * elements as one individual item regardless of how many elements are
+ * in the list.  This means different queries jumble to the same query_id,
+ * if the only difference is the number of elements in the list.
+ *
+ * If query_id_squash_values is disabled or the list is not "simple
+ * enough", we jumble each element normally.
+ */
+static void
+_jumbleElements(JumbleState *jstate, List *elements)
+{
+	Node	   *first,
+			   *last;
+
+	if (IsSquashableConstList(elements, &first, &last))
+	{
+		/*
+		 * If this list of elements is squashable, keep track of the location
+		 * of its first and last elements.  When reading back the locations
+		 * array, we'll see two consecutive locations with ->squashed set to
+		 * true, indicating the location of initial and final elements of this
+		 * list.
+		 *
+		 * For the limited set of cases we support now (implicit coerce via
+		 * FuncExpr, Const) it's fine to use exprLocation of the 'last'
+		 * expression, but if more complex composite expressions are to be
+		 * supported (e.g., OpExpr or FuncExpr as an explicit call), more
+		 * sophisticated tracking will be needed.
+		 */
+		RecordConstLocation(jstate, exprLocation(first), true);
+		RecordConstLocation(jstate, exprLocation(last), true);
+	}
+	else
+	{
+		_jumbleNode(jstate, (Node *) elements);
+	}
+}
+
 static void
 _jumbleNode(JumbleState *jstate, Node *node)
 {
diff --git a/src/backend/postmaster/launch_backend.c b/src/backend/postmaster/launch_backend.c
index 77fb877dbad..78d8b652e04 100644
--- a/src/backend/postmaster/launch_backend.c
+++ b/src/backend/postmaster/launch_backend.c
@@ -115,6 +115,7 @@ typedef struct
 	bool		redirection_done;
 	bool		IsBinaryUpgrade;
 	bool		query_id_enabled;
+	bool		query_id_squash_values;
 	int			max_safe_fds;
 	int			MaxBackends;
 	int			num_pmchild_slots;
@@ -775,6 +776,7 @@ save_backend_variables(BackendParameters *param,
 	param->redirection_done = redirection_done;
 	param->IsBinaryUpgrade = IsBinaryUpgrade;
 	param->query_id_enabled = query_id_enabled;
+	param->query_id_squash_values = query_id_squash_values;
 	param->max_safe_fds = max_safe_fds;
 
 	param->MaxBackends = MaxBackends;
@@ -1035,6 +1037,7 @@ restore_backend_variables(BackendParameters *param)
 	redirection_done = param->redirection_done;
 	IsBinaryUpgrade = param->IsBinaryUpgrade;
 	query_id_enabled = param->query_id_enabled;
+	query_id_squash_values = param->query_id_squash_values;
 	max_safe_fds = param->max_safe_fds;
 
 	MaxBackends = param->MaxBackends;
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 9c0b10ad4dc..fb7515a3156 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -2118,6 +2118,16 @@ struct config_bool ConfigureNamesBool[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"query_id_squash_values", PGC_USERSET, STATS_MONITORING,
+			gettext_noop("Allows to merge constants in a list when computing "
+						 "query_id."),
+		},
+		&query_id_squash_values,
+		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 8de86e0c945..c223338302c 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -652,6 +652,7 @@
 # - Monitoring -
 
 #compute_query_id = auto
+#query_id_squash_values = off
 #log_statement_stats = off
 #log_parser_stats = off
 #log_planner_stats = off
diff --git a/src/include/nodes/nodes.h b/src/include/nodes/nodes.h
index 580238bfab1..d18044b4e65 100644
--- a/src/include/nodes/nodes.h
+++ b/src/include/nodes/nodes.h
@@ -105,6 +105,8 @@ typedef enum NodeTag
  *   that typmod and collation information are usually irrelevant for the
  *   query jumbling.
  *
+ * - query_jumble_squash: Squash multiple values during query jumbling.
+ *
  * - query_jumble_location: Mark the field as a location to track.  This is
  *   only allowed for integer fields that include "location" in their name.
  *
diff --git a/src/include/nodes/primnodes.h b/src/include/nodes/primnodes.h
index d0576da3e25..7d3b4198f26 100644
--- a/src/include/nodes/primnodes.h
+++ b/src/include/nodes/primnodes.h
@@ -1394,7 +1394,7 @@ typedef struct ArrayExpr
 	/* common type of array elements */
 	Oid			element_typeid pg_node_attr(query_jumble_ignore);
 	/* the array elements or sub-arrays */
-	List	   *elements;
+	List	   *elements pg_node_attr(query_jumble_squash);
 	/* true if elements are sub-arrays */
 	bool		multidims pg_node_attr(query_jumble_ignore);
 	/* token location, or -1 if unknown */
diff --git a/src/include/nodes/queryjumble.h b/src/include/nodes/queryjumble.h
index 50eb9566587..905f66bc0bd 100644
--- a/src/include/nodes/queryjumble.h
+++ b/src/include/nodes/queryjumble.h
@@ -23,6 +23,12 @@ typedef struct LocationLen
 {
 	int			location;		/* start offset in query text */
 	int			length;			/* length in bytes, or -1 to ignore */
+
+	/*
+	 * Indicates that this location represents the beginning or end of a run
+	 * of squashed constants.
+	 */
+	bool		squashed;
 } LocationLen;
 
 /*
@@ -68,6 +74,7 @@ extern JumbleState *JumbleQuery(Query *query);
 extern void EnableQueryId(void);
 
 extern PGDLLIMPORT bool query_id_enabled;
+extern PGDLLIMPORT bool query_id_squash_values;
 
 /*
  * Returns whether query identifier computation has been enabled, either
-- 
2.39.5

--xulb2npnegtuim3q--