review:tracking temporary files in pg_stat_database

Hello

This is review of Tomas' patch for counting of using temporary files:

* This patch was cleanly applied and code was compiled
* All 128 tests passed
* There are own regress tests, but usually pg_stat_* functions are not tested
* There is adequate documentation
* This patch was requested
http://archives.postgresql.org/pgsql-hackers/2011-12/msg00950.php
* Code following postgresql coding standards
* Code works

postgres=# create table xx(a int);
CREATE TABLE
postgres=# insert into xx select (random()*100000)::int from
generate_series(1,200000);
INSERT 0 200000
postgres=# \d+ xx;
Table "public.xx"
Column | Type | Modifiers | Storage | Stats target | Description
--------+---------+-----------+---------+--------------+-------------
a | integer | | plain | |
Has OIDs: no

postgres=# \dt+ xx;
List of relations
Schema | Name | Type | Owner | Size | Description
--------+------+-------+-------+---------+-------------
public | xx | table | pavel | 7104 kB |
(1 row)

postgres=# set work_mem to '1MB';
SET
postgres=# select
pg_stat_get_db_temp_bytes(12899),pg_stat_get_db_temp_files(12899);
pg_stat_get_db_temp_bytes | pg_stat_get_db_temp_files
---------------------------+---------------------------
9889486560 | 4103
(1 row)

postgres=# select * from xx order by 1;

postgres=# select
pg_stat_get_db_temp_bytes(12899),pg_stat_get_db_temp_files(12899);
pg_stat_get_db_temp_bytes | pg_stat_get_db_temp_files
---------------------------+---------------------------
9892288224 | 4104
(1 row)

This patch is ready for commit

Regards

Pavel Stehule