[PATCH] pg_stat_statements dealloc field ignores manual deallocation

Hi,

This is a proposal of a patch for pg_stat_statements extension. It
corrects deallocation events accounting.

Since 2e0fedf there is a view pg_stat_statements_info is available in
pg_stat_statements extension. It has a dealloc field, that should be a
counter of deallocation events happened.
Right now it accounts only automatic deallocation events, happened when
we need a place for a new statement, but manual deallocation events
caused by pg_stat_statements_reset() function for some subset of
collected statements is not accounted.
My opinion is that manual deallocation is a deallocation too and it
must be accounted in dealloc field of pg_stat_statements_info view.

Let's see how it happens:

postgres=# select pg_stat_statements_reset();
postgres=# select 1;
?column?
----------
1
(1 row)
postgres=# select dealloc from pg_stat_statements_info ;
dealloc
---------
0
(1 row)

postgres=# select pg_stat_statements_reset(userid,dbid,queryid)
postgres-# from pg_stat_statements where query = 'select $1';
pg_stat_statements_reset
--------------------------

(1 row)

postgres=# select dealloc from pg_stat_statements_info ;
dealloc
---------
0 -- Here must be a one now, as deallocation happened
(1 row)

This patch adds accounting of manual deallocation events.

--
Andrei Zubkov
Postgres Professional
The Russian Postgres Company