It is essential to restart the PostgreSQL instance. After that, execute the following query in psql:

CREATE EXTENSION pg_query_state;

Done!

Tests using parallel sessionsusing python 2.7 script:

Test using parallel sessionswith Python 2.7/3+ compatible script:

python tests/pg_qs_test_runner.py [OPTION]...

*prerequisite packages*:

*`psycopg2` version 2.6 or later

*`PyYAML` version 3.11 or later

*`progressbar2` for stress test progress reporting

*options*:

**- -host* --- postgres server host, default value is*localhost*

**- -port* --- postgres server port, default value is*5432*

**- -database* --- database name, default value is*postgres*

**- -user* --- user name, default value is*postgres*

**- -password* --- user's password, default value is empty

Or run all tests in`Docker` using:

export LEVEL=stress

export PG_VERSION=12

docker-compose build

docker-compose run tests

There are different test levels:`hardcore`,`nightmare` (runs tests under`valgrind`) and`stress` (runs tests under`TPC-DS` load).

pg_query_state(integer pid,

Set maximum number of parallel workers on`gather` node equals`2`:

postgres=# set max_parallel_workers_per_gather = 2;

Assume one backend with pid = 49265 performs a simple query:

postgres=# select pg_backend_pid();

pg_backend_pid

postgres=# select count(*) from foo join bar on foo.c1=bar.c1;

Other backend can extract intermediate state of execution that query:

postgres=# \x

postgres=# select * from pg_query_state(49265);

-[ RECORD1 ]+-------------------------------------------------------------------------------------------------------------------------

`Seq Scan` node has statistics on passed loops (average number of rows delivered to`Nested Loop` and number of passed loops are shown) and statistics on current loop. Other nodes has statistics only for current loop as this loop is first (`loop number` = 1).

Assume first backend executes some function:

postgres=# select n_join_foo_bar();

Other backend can get the follow output:

postgres=# select * from pg_query_state(49265);

-[ RECORD1 ]+------------------------------------------------------------------------------------------------------------------

pid |49265

First row corresponds to function call, second - to query which is in the body of that function.

We can get result plans in different format (e.g.`json`):

postgres=# select * from pg_query_state(pid := 49265, format := 'json');

-[ RECORD1 ]+------------------------------------------------------------

pid |49265