Re: pg_stat_statements: calls under-estimation propagation

From: pilum(dot)70(at)uni-muenster(dot)de
To: pgsql-hackers(at)postgresql(dot)org
Subject: Re: pg_stat_statements: calls under-estimation propagation
Date: 2013-10-10 10:11:03
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The V7-Patch applied cleanly and I got no issues in my first tests.

The change from column session_start to a function seems very reasonable for

Concernig the usability, I would like to suggest a minor change, that massively
increases the usefulness of the patch for beginners, who often use this view as
a first approach to optimize index structure.

The history of this tool contains a first version without normalization.
This wasn't useful enough except for prepared queries.
The actual version has normalized queries, so calls get
summarized to get a glimpse of bad queries.
But the drawback of this approach is impossibility to use
explain analyze without further substitutions.

The identification patch provides the possibility to summarize calls
by query_id, so that the normalized query string itself is no longer needed to
be exposed in the view for everyone.

I suggest to add a parameter to recover the possibility to
display real queries. The following very minor change
(based on V7) exposes the first real query getting this
query_id if normalization of the exposed string ist deactivated (The actual
behaviour is the default). This new option is not always the best starting
point to discover index shortfalls, but a huge gain for beginners because it
serves the needs
in more than 90% of the normal use cases.

What do you think?


P.S. This message is resent, because it is stalled two days, so sorry for a possible duplicate

Date: Mon Oct 7 17:54:08 2013 +0000

Switch to disable normalized query strings

diff --git a/contrib/pg_stat_statements/pg_stat_statements.c
index e50dfba..6cc9244 100644
--- a/contrib/pg_stat_statements/pg_stat_statements.c
+++ b/contrib/pg_stat_statements/pg_stat_statements.c
@@ -234,7 +234,7 @@ static int pgss_max; /* max # statements to track */
static int pgss_track; /* tracking level */
static bool pgss_track_utility; /* whether to track utility commands */
static bool pgss_save; /* whether to save stats across shutdown */
+static bool pgss_normalize; /* whether to normalize the query representation shown in the view (otherwise show the first query executed with this query_id) */

#define pgss_enabled() \
(pgss_track == PGSS_TRACK_ALL || \
@@ -356,6 +356,17 @@ _PG_init(void)

+ DefineCustomBoolVariable("pg_stat_statements.normalize",
+ "Selects whether the view column contains the query strings in a normalized form.",
+ &pgss_normalize,
+ true,
+ 0,
+ NULL);

@@ -1084,9 +1095,9 @@ pgss_store(const char *query, uint32 queryId,

query_len = strlen(query);

- if (jstate)
+ if (jstate && pgss_normalize)
- /* Normalize the string if enabled */
+ /* Normalize the string is not NULL and normalized query strings are enabled */
norm_query = generate_normalized_query(jstate, query,


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