limiting collected query text length in pg_stat_statements

Greetings,

I want to limit the query text that gets captured in pg_stat_statements. We have sql statements with thousands of values clauses (upwards of 10,000) that run at a 1 second interval. When just a handful are running plus 2 or 3 loads using the same technique (10,000 entry values clauses) querying the pg_stat_statements table gets bogged down (see below). With the pg_stat_statements.max is set to 1000 statements just querying the table stats table seems to impact the running statements! I have temporarily staved off the issue by reducing the max to 250 statements, and I have made recommendations to the development team to cut down the number of values clauses. However, it seems to me that the ability to truncate the captured query would be a useful feature.

I've peeked at the source code and I don't see the track_activity_query_size used (pg_stat_activity.query) which would be one mechanism. I don't really know what would be the right way to do this or even if it is a good idea, i.e. if limiting that would have a larger impact to the statistics ecosystem...

Thoughts or suggestions?
Regards,
pg

# select length(query) from pg_stat_statements;

length

---------

876153

879385

171

44

3796

873527

<snip>

896454

864538

1869286

938

869891

<snip>

883526

877365

(969 rows)

Time: 9898.411 ms (00:09.898)

# select count(*) from pg_stat_statements;

count

-------

971

(1 row)

Time: 6457.985 ms (00:06.458)

Using showtext:=false shows the impact of the large columns:

# select count(*) from pg_stat_statements(showtext:=false);

count

-------

970

(1 row)

Time: 10.644 ms

Phil Godfrin | Database Administration
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