pg_stat_statements: Fix parameter number gaps in normalized queries

pg_stat_statements anticipates that certain constant locations may be
recorded multiple times and attempts to avoid calculating a length for
these locations in fill_in_constant_lengths().

However, during generate_normalized_query() where normalized query
strings are generated, these locations are not excluded from
consideration.  This could increment the parameter number counter for
every recorded occurrence at such a location, leading to an incorrect
normalization in certain cases with gaps in the numbers reported.

For example, take this query:
SELECT WHERE '1' IN ('2'::int, '3'::int::text)
Before this commit, it would be normalized like that, with gaps in the
parameter numbers:
SELECT WHERE $1 IN ($3::int, $4::int::text)
However the correct, less confusing one should be like that:
SELECT WHERE $1 IN ($2::int, $3::int::text)

This commit fixes the computation of the parameter numbers to track the
number of constants replaced with an $n by a separate counter instead of
the iterator used to loop through the list of locations.

The underlying query IDs are not changed, neither are the normalized
strings for existing PGSS hash entries.  New entries with fresh
normalized queries would automatically get reshaped based on the new
parameter numbering.

Issue discovered while discussing a separate problem for HEAD, but this
affects all the stable branches.

Author: Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAA5RZ0tzxvWXsacGyxrixdhy3tTTDfJQqxyFBRFh31nNHBQ5qA@mail.gmail.com
Backpatch-through: 13

diff --git a/contrib/pg_stat_statements/expected/pg_stat_statements.out b/contrib/pg_stat_statements/expected/pg_stat_statements.out
index b52d1877223659ea01210391fa4ebd76795d2ed6..0c03565f2e6569ffdcf4a56758b1f097a0c7e601 100644 (file)
--- a/contrib/pg_stat_statements/expected/pg_stat_statements.out
+++ b/contrib/pg_stat_statements/expected/pg_stat_statements.out
@@ -398,6 +398,35 @@ SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
  SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C" |     0 |    0
 (6 rows)
 
+-- normalization of constants and parameters, with constant locations
+-- recorded one or more times.
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+ t 
+---
+ t
+(1 row)
+
+SELECT WHERE '1' IN ('1'::int, '3'::int::text);
+--
+(1 row)
+
+SELECT WHERE (1, 2) IN ((1, 2), (2, 3));
+--
+(1 row)
+
+SELECT WHERE (3, 4) IN ((5, 6), (8, 7));
+--
+(0 rows)
+
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+                                 query                                  | calls 
+------------------------------------------------------------------------+-------
+ SELECT WHERE $1 IN ($2::int, $3::int::text)                            |     1
+ SELECT WHERE ($1, $2) IN (($3, $4), ($5, $6))                          |     2
+ SELECT pg_stat_statements_reset() IS NOT NULL AS t                     |     1
+ SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C" |     0
+(4 rows)
+
 --
 -- queries with locking clauses
 --

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c b/contrib/pg_stat_statements/pg_stat_statements.c
index 1ec5525276aa8e5f450ad9f383370d4981cd8e74..f2332312ba31668e8ef6b5fdcddce791592c94ad 100644 (file)
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -2640,6 +2640,7 @@ 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 */
+       int                     num_constants_replaced = 0;
 
        /*
         * Get constants' lengths (core system only gives us locations).  Note
@@ -2683,7 +2684,8 @@ generate_normalized_query(JumbleState *jstate, const char *query,
 
                /* 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);
+                                                         num_constants_replaced + 1 + jstate->highest_extern_param_id);
+               num_constants_replaced++;
 
                quer_loc = off + tok_len;
                last_off = off;

diff --git a/contrib/pg_stat_statements/sql/pg_stat_statements.sql b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
index dffd2c8c18707bbb317b40bc320fc4e4c8bb9470..45f9cd29b77fb36f26166570d4beba41dba61ed6 100644 (file)
--- a/contrib/pg_stat_statements/sql/pg_stat_statements.sql
+++ b/contrib/pg_stat_statements/sql/pg_stat_statements.sql
@@ -201,6 +201,14 @@ SELECT PLUS_ONE(1);
 
 SELECT query, calls, rows FROM pg_stat_statements ORDER BY query COLLATE "C";
 
+-- normalization of constants and parameters, with constant locations
+-- recorded one or more times.
+SELECT pg_stat_statements_reset() IS NOT NULL AS t;
+SELECT WHERE '1' IN ('1'::int, '3'::int::text);
+SELECT WHERE (1, 2) IN ((1, 2), (2, 3));
+SELECT WHERE (3, 4) IN ((5, 6), (8, 7));
+SELECT query, calls FROM pg_stat_statements ORDER BY query COLLATE "C";
+
 --
 -- queries with locking clauses
 --