New module postgresql_set - Change a PostgreSQL server configuration parameter (#51875)

* New module postgresql_set - Change a PostgreSQL server configuration parameter

* New module postgresql_set - fix

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* New module postgresql_set - fix tests

* Various cosmetic and docs changes

* New module postgresql_set - add returned value

* New module postgresql_set - add returned value

* New module postgresql_set - add check mode

* New module postgresql_set - fix comment

* New module postgresql_set - added CI tests for check_mode

* New module postgresql_set - added aliases, fix typos

* New module postgresql_set - fix

* New module postgresql_set - fix sanity

* New module postgresql_set - fixes

* New module postgresql_set - fixes

* New module postgresql_set - fixes

lib/ansible/modules/database/postgresql/postgresql_set.py

@@ -0,0 +1,528 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+
+# Copyright: (c) 2018, Andrew Klychkov (@Andersson007) <aaklychkov@mail.ru>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+
+from __future__ import absolute_import, division, print_function
+__metaclass__ = type
+
+ANSIBLE_METADATA = {
+    'metadata_version': '1.1',
+    'status': ['preview'],
+    'supported_by': 'community'
+}
+
+DOCUMENTATION = r'''
+---
+module: postgresql_set
+short_description: Change a PostgreSQL server configuration parameter
+description:
+   - Allows to change a PostgreSQL server configuration parameter.
+   - The module uses ALTER SYSTEM command U(https://www.postgresql.org/docs/current/sql-altersystem.html)
+     and applies changes by reload server configuration.
+   - ALTER SYSTEM is used for changing server configuration parameters across the entire database cluster.
+   - It can be more convenient and safe than the traditional method of manually editing the postgresql.conf file.
+   - ALTER SYSTEM writes the given parameter setting to the $PGDATA/postgresql.auto.conf file,
+     which is read in addition to postgresql.conf U(https://www.postgresql.org/docs/current/sql-altersystem.html).
+   - The module allows to reset parameter to boot_val (cluster initial value) by I(reset=yes) or remove parameter
+     string from postgresql.auto.conf and reload I(value=default) (for settings with postmaster context restart is required).
+   - After change you can see in the ansible output the previous and
+     the new parameter value and other information using returned values and M(debug) module.
+version_added: "2.8"
+options:
+  name:
+    description:
+    - Name of PostgreSQL server parameter.
+    type: str
+    required: true
+  value:
+    description:
+    - Parameter value to set.
+    - To remove parameter string from postgresql.auto.conf and
+      reload the server configuration you must pass I(value=default).
+      With I(value=default) the playbook always returns changed is true.
+    type: str
+    required: true
+  reset:
+    description:
+    - Restore parameter to initial state (boot_val). Mutually exclusive with I(value).
+    type: bool
+    default: false
+  session_role:
+    description:
+    - Switch to session_role after connecting. The specified session_role must
+      be a role that the current login_user is a member of.
+    - Permissions checking for SQL commands is carried out as though
+      the session_role were the one that had logged in originally.
+    type: str
+  db:
+    description:
+    - Name of database to connect.
+    type: str
+    aliases:
+    - login_db
+  port:
+    description:
+    - Database port to connect.
+    type: int
+    default: 5432
+    aliases:
+    - login_port
+  login_user:
+    description:
+    - User (role) used to authenticate with PostgreSQL.
+    type: str
+    default: postgres
+  login_password:
+    description:
+    - Password used to authenticate with PostgreSQL.
+    type: str
+  login_host:
+    description:
+    - Host running PostgreSQL.
+    type: str
+  login_unix_socket:
+    description:
+    - Path to a Unix domain socket for local connections.
+    type: str
+  ssl_mode:
+    description:
+    - Determines whether or with what priority a secure SSL TCP/IP connection
+      will be negotiated with the server.
+    - See U(https://www.postgresql.org/docs/current/static/libpq-ssl.html) for
+      more information on the modes.
+    - Default of C(prefer) matches libpq default.
+    type: str
+    choices: [ allow, disable, prefer, require, verify-ca, verify-full ]
+    default: prefer
+  ssl_rootcert:
+    description:
+    - Specifies the name of a file containing SSL certificate authority (CA)
+      certificate(s).
+    - If the file exists, the server's certificate will be
+      verified to be signed by one of these authorities.
+    type: str
+notes:
+- Supported version of PostgreSQL is 9.4 and later.
+- Pay attention, change setting with 'postmaster' context can return changed is true
+  when actually nothing changes because the same value may be presented in
+  several different form, for example, 1024MB, 1GB, etc. However in pg_settings
+  system view it can be defined like 131072 number of 8kB pages.
+  The final check of the parameter value cannot compare it because the server was
+  not restarted and the value in pg_settings is not updated yet.
+- For some parameters restart of PostgreSQL server is required.
+  See official documentation U(https://www.postgresql.org/docs/current/view-pg-settings.html).
+- The default authentication assumes that you are either logging in as or
+  sudo'ing to the postgres account on the host.
+- This module uses psycopg2, a Python PostgreSQL database adapter. You must
+  ensure that psycopg2 is installed on the host before using this module. If
+  the remote host is the PostgreSQL server (which is the default case), then
+  PostgreSQL must also be installed on the remote host. For Ubuntu-based
+  systems, install the postgresql, libpq-dev, and python-psycopg2 packages
+  on the remote host before using this module.
+requirements: [ psycopg2 ]
+author:
+- Andrew Klychkov (@Andersson007)
+'''
+
+EXAMPLES = r'''
+- name: Restore wal_keep_segments parameter to initial state
+  postgresql_set:
+    name: wal_keep_segments
+    reset: yes
+
+# Set work_mem parameter to 32MB and show what's been changed and restart is required or not
+# (output example: "msg": "work_mem 4MB >> 64MB restart_req: False")
+- name: Set work mem parameter
+  postgresql_set:
+    name: work_mem
+    value: 32mb
+    register: set
+
+- debug:
+    msg: "{{ set.name }} {{ set.prev_val_pretty }} >> {{ set.value_pretty }} restart_req: {{ set.restart_required }}"
+  when: set.changed
+# Ensure that the restart of PostgreSQL serever must be required for some parameters.
+# In this situation you see the same parameter in prev_val and value_prettyue, but 'changed=True'
+# (If you passed the value that was different from the current server setting).
+
+- name: Set log_min_duration_statement parameter to 1 second
+  postgresql_set:
+    name: log_min_duration_statement
+    value: 1s
+
+- name: Set wal_log_hints parameter to default value (remove parameter from postgresql.auto.conf)
+  postgresql_set:
+    name: wal_log_hints
+    value: default
+'''
+
+RETURN = r'''
+name:
+  description: Name of PostgreSQL server parameter.
+  returned: always
+  type: str
+  sample: 'shared_buffers'
+restart_required:
+  description: Information about parameter current state.
+  returned: always
+  type: bool
+  sample: true
+prev_val_pretty:
+  description: Information about previous state of the parameter.
+  returned: always
+  type: str
+  sample: '4MB'
+value_pretty:
+  description: Information about current state of the parameter.
+  returned: always
+  type: str
+  sample: '64MB'
+value:
+  description:
+  - Dictionary that contains the current parameter value (at the time of playbook finish).
+  - Pay attention that for real change some parameters restart of PostgreSQL server is required.
+  - Returns the current value in the check mode.
+  returned: always
+  type: dict
+  sample: { "value": 67108864, "unit": "b" }
+context:
+  description:
+  - PostgreSQL setting context.
+  returned: always
+  type: str
+  sample: user
+'''
+
+PG_REQ_VER = 90400
+
+from copy import deepcopy
+
+try:
+    import psycopg2
+    HAS_PSYCOPG2 = True
+except ImportError:
+    HAS_PSYCOPG2 = False
+
+from ansible.module_utils.basic import AnsibleModule
+from ansible.module_utils.database import SQLParseError
+from ansible.module_utils.postgres import postgres_common_argument_spec
+from ansible.module_utils.six import iteritems
+from ansible.module_utils._text import to_native
+
+
+# To allow to set value like 1mb instead of 1MB, etc:
+POSSIBLE_SIZE_UNITS = ("mb", "gb", "tb")
+
+# ===========================================
+# PostgreSQL module specific support methods.
+#
+
+
+def param_get(cursor, module, name):
+    query = ("SELECT name, setting, unit, context, boot_val "
+             "FROM pg_settings WHERE name = '%s'" % name)
+    try:
+        cursor.execute(query)
+        info = cursor.fetchall()
+        cursor.execute("SHOW %s" % name)
+        val = cursor.fetchone()
+
+    except Exception as e:
+        module.fail_json(msg="Unable to get %s value due to : %s" % (name, to_native(e)))
+
+    raw_val = info[0][1]
+    unit = info[0][2]
+    context = info[0][3]
+    boot_val = info[0][4]
+
+    if val[0] == 'True':
+        val[0] = 'on'
+    elif val[0] == 'False':
+        val[0] = 'off'
+
+    if unit == 'kB':
+        if int(raw_val) > 0:
+            raw_val = int(raw_val) * 1024
+        if int(boot_val) > 0:
+            boot_val = int(boot_val) * 1024
+
+        unit = 'b'
+
+    elif unit == 'MB':
+        if int(raw_val) > 0:
+            raw_val = int(raw_val) * 1024 * 1024
+        if int(boot_val) > 0:
+            boot_val = int(boot_val) * 1024 * 1024
+
+        unit = 'b'
+
+    return (val[0], raw_val, unit, boot_val, context)
+
+
+def pretty_to_bytes(pretty_val):
+    # The function returns a value in bytes
+    # if the value contains 'B', 'kB', 'MB', 'GB', 'TB'.
+    # Otherwise it returns the passed argument.
+
+    val_in_bytes = None
+
+    if 'kB' in pretty_val:
+        num_part = int(''.join(d for d in pretty_val if d.isdigit()))
+        val_in_bytes = num_part * 1024
+
+    elif 'MB' in pretty_val.upper():
+        num_part = int(''.join(d for d in pretty_val if d.isdigit()))
+        val_in_bytes = num_part * 1024 * 1024
+
+    elif 'GB' in pretty_val.upper():
+        num_part = int(''.join(d for d in pretty_val if d.isdigit()))
+        val_in_bytes = num_part * 1024 * 1024 * 1024
+
+    elif 'TB' in pretty_val.upper():
+        num_part = int(''.join(d for d in pretty_val if d.isdigit()))
+        val_in_bytes = num_part * 1024 * 1024 * 1024 * 1024
+
+    elif 'B' in pretty_val.upper():
+        num_part = int(''.join(d for d in pretty_val if d.isdigit()))
+        val_in_bytes = num_part
+
+    else:
+        return pretty_val
+
+    return val_in_bytes
+
+
+def param_set(cursor, module, name, value, context):
+    try:
+        if str(value).lower() == 'default':
+            query = "ALTER SYSTEM SET %s = DEFAULT" % name
+        else:
+            query = "ALTER SYSTEM SET %s = '%s'" % (name, value)
+        cursor.execute(query)
+
+        if context != 'postmaster':
+            cursor.execute("SELECT pg_reload_conf()")
+
+    except Exception as e:
+        module.fail_json(msg="Unable to get %s value due to : %s" % (name, to_native(e)))
+
+    return True
+
+
+def connect_to_db(module, kw, autocommit=False):
+    try:
+        db_connection = psycopg2.connect(**kw)
+        if autocommit:
+            db_connection.set_session(autocommit=True)
+
+    except TypeError as e:
+        if 'sslrootcert' in e.args[0]:
+            module.fail_json(msg='Postgresql server must be at least version 8.4 to support sslrootcert')
+        module.fail_json(msg="unable to connect to database: %s" % to_native(e))
+    except Exception as e:
+        module.fail_json(msg="unable to connect to database: %s" % to_native(e))
+
+    return db_connection
+
+# ===========================================
+# Module execution.
+#
+
+
+def main():
+    argument_spec = postgres_common_argument_spec()
+    argument_spec.update(
+        name=dict(type='str', required=True),
+        db=dict(type='str', aliases=['login_db']),
+        port=dict(type='int', default=5432, aliases=['login_port']),
+        ssl_mode=dict(type='str', default='prefer', choices=['allow', 'disable', 'prefer', 'require', 'verify-ca', 'verify-full']),
+        ssl_rootcert=dict(type='str'),
+        value=dict(type='str'),
+        reset=dict(type='bool'),
+        session_role=dict(type='str'),
+    )
+    module = AnsibleModule(
+        argument_spec=argument_spec,
+        supports_check_mode=True,
+    )
+
+    if not HAS_PSYCOPG2:
+        module.fail_json(msg="the python psycopg2 module is required")
+
+    name = module.params["name"]
+    value = module.params["value"]
+    reset = module.params["reset"]
+    sslrootcert = module.params["ssl_rootcert"]
+    session_role = module.params["session_role"]
+
+    # Allow to pass values like 1mb instead of 1MB, etc:
+    if value:
+        for unit in POSSIBLE_SIZE_UNITS:
+            if unit in value:
+                value = value.upper()
+
+    if value and reset:
+        module.fail_json(msg="%s: value and reset params are mutually exclusive" % name)
+
+    if not value and not reset:
+        module.fail_json(msg="%s: at least one of value or reset param must be specified" % name)
+
+    # To use defaults values, keyword arguments must be absent, so
+    # check which values are empty and don't include in the **kw
+    # dictionary
+    params_map = {
+        "login_host": "host",
+        "login_user": "user",
+        "login_password": "password",
+        "port": "port",
+        "db": "database",
+        "ssl_mode": "sslmode",
+        "ssl_rootcert": "sslrootcert"
+    }
+    kw = dict((params_map[k], v) for (k, v) in iteritems(module.params)
+              if k in params_map and v != '' and v is not None)
+
+    # Store connection parameters for the final check:
+    con_params = deepcopy(kw)
+
+    # If a login_unix_socket is specified, incorporate it here.
+    is_localhost = "host" not in kw or kw["host"] is None or kw["host"] == "localhost"
+    if is_localhost and module.params["login_unix_socket"] != "":
+        kw["host"] = module.params["login_unix_socket"]
+
+    if psycopg2.__version__ < '2.4.3' and sslrootcert:
+        module.fail_json(msg='psycopg2 must be at least 2.4.3 '
+                             'in order to user the ssl_rootcert parameter')
+
+    db_connection = connect_to_db(module, kw, autocommit=True)
+    cursor = db_connection.cursor(cursor_factory=psycopg2.extras.DictCursor)
+
+    # Check server version (needs 9.4 or later):
+    cursor.execute("select current_setting('server_version_num')")
+    ver = int(cursor.fetchone()[0])
+    if ver < PG_REQ_VER:
+        module.warn("PostgreSQL is %s version but %s or later is required" % (ver, PG_REQ_VER))
+        kw = dict(
+            changed=False,
+            restart_required=False,
+            value_pretty="",
+            prev_val_pretty="",
+            value={"value": "", "unit": ""},
+        )
+        kw['name'] = name
+        db_connection.close()
+        module.exit_json(**kw)
+
+    # Switch role, if specified:
+    if session_role:
+        try:
+            cursor.execute('SET ROLE %s' % session_role)
+        except Exception as e:
+            module.fail_json(msg="Could not switch role: %s" % to_native(e))
+
+    # Set default returned values:
+    restart_required = False
+    changed = False
+    kw['name'] = name
+    kw['restart_required'] = False
+
+    # Get info about param state:
+    res = param_get(cursor, module, name)
+    current_value = res[0]
+    raw_val = res[1]
+    unit = res[2]
+    boot_val = res[3]
+    context = res[4]
+
+    if value == 'True':
+        value = 'on'
+    elif value == 'False':
+        value = 'off'
+
+    kw['prev_val_pretty'] = current_value
+    kw['value_pretty'] = deepcopy(kw['prev_val_pretty'])
+    kw['context'] = context
+
+    # Do job
+    if context == "internal":
+        module.fail_json(msg="%s: cannot be changed (internal context). See "
+                             "https://www.postgresql.org/docs/current/runtime-config-preset.html" % name)
+
+    if context == "postmaster":
+        restart_required = True
+
+    # If check_mode, just compare and exit:
+    if module.check_mode:
+        if pretty_to_bytes(value) == pretty_to_bytes(current_value):
+            kw['changed'] = False
+
+        else:
+            kw['value_pretty'] = value
+            kw['changed'] = True
+
+        # Anyway returns current raw value in the check_mode:
+        kw['value'] = dict(
+            value=raw_val,
+            unit=unit,
+        )
+        kw['restart_required'] = restart_required
+        module.exit_json(**kw)
+
+    # Set param:
+    if value and value != current_value:
+        changed = param_set(cursor, module, name, value, context)
+
+        kw['value_pretty'] = value
+
+    # Reset param:
+    elif reset:
+        if raw_val == boot_val:
+            # nothing to change, exit:
+            kw['value'] = dict(
+                value=raw_val,
+                unit=unit,
+            )
+            module.exit_json(**kw)
+
+        changed = param_set(cursor, module, name, boot_val, context)
+
+    if restart_required:
+        module.warn("Restart of PostgreSQL is required for setting %s" % name)
+
+    cursor.close()
+    db_connection.close()
+
+    # Reconnect and recheck current value:
+    if context in ('sighup', 'superuser-backend', 'backend', 'superuser', 'user'):
+        db_connection = connect_to_db(module, con_params, autocommit=True)
+        cursor = db_connection.cursor(cursor_factory=psycopg2.extras.DictCursor)
+
+        res = param_get(cursor, module, name)
+        # f_ means 'final'
+        f_value = res[0]
+        f_raw_val = res[1]
+
+        if raw_val == f_raw_val:
+            changed = False
+
+        else:
+            changed = True
+
+        kw['value_pretty'] = f_value
+        kw['value'] = dict(
+            value=f_raw_val,
+            unit=unit,
+        )
+
+        cursor.close()
+        db_connection.close()
+
+    kw['changed'] = changed
+    kw['restart_required'] = restart_required
+    module.exit_json(**kw)
+
+
+if __name__ == '__main__':
+    main()

test/integration/targets/postgresql/tasks/main.yml

@@ -762,6 +762,10 @@
     that:
       - "result.stdout_lines[-1] == '(0 rows)'"
 
+# Test postgresql_set
+- include: postgresql_set.yml
+  when: postgres_version_resp.stdout is version('9.4', '>=')
+
 # Verify different session_role scenarios
 - include: session_role.yml
 

test/integration/targets/postgresql/tasks/postgresql_set.yml

@@ -0,0 +1,232 @@
+# Test code for the postgresql_set module
+# Copyright: (c) 2019, Andrew Klychkov (@Andersson007) <aaklychkov@mail.ru>
+# GNU General Public License v3.0+ (see COPYING or https://www.gnu.org/licenses/gpl-3.0.txt)
+#
+# Notice: assertions are different for Ubuntu 16.04 and FreeBSD because they don't work
+# correctly for these tests. There are some stranges exactly in Shippable CI.
+# However I checked it manually for all points and it worked as expected.
+
+- name: postgresql_set - preparation to the next step
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    reset: yes
+  ignore_errors: yes
+
+- name: postgresql_set - set work_mem (restart is not required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    value: 12MB
+  register: set_wm
+  ignore_errors: yes
+
+- assert:
+    that:
+      - set_wm.name == 'work_mem'
+      - set_wm.changed == true
+      - set_wm.value_pretty == '12MB'
+      - set_wm.value_pretty != set_wm.prev_val_pretty
+      - set_wm.restart_required == false
+      - set_wm.value.value == 12582912
+      - set_wm.value.unit == 'b'
+  when: ansible_distribution != "Ubuntu" and ansible_distribution_major_version != '16' and ansible_distribution != "FreeBSD"
+
+- assert:
+    that:
+      - set_wm.name == 'work_mem'
+      - set_wm.changed == true
+      - set_wm.restart_required == false
+  when: ansible_distribution == "Ubuntu" and ansible_distribution_major_version == '16'
+
+- name: postgresql_set - reset work_mem (restart is not required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    reset: yes
+  register: reset_wm
+  ignore_errors: yes
+
+- assert:
+    that:
+      - reset_wm.name == 'work_mem'
+      - reset_wm.changed == true
+      - reset_wm.value_pretty != reset_wm.prev_val_pretty
+      - reset_wm.restart_required == false
+      - reset_wm.value.value != '12582912' 
+  when: ansible_distribution != "Ubuntu" and ansible_distribution_major_version != '16' and ansible_distribution != "FreeBSD"
+
+- assert:
+    that:
+      - reset_wm.name == 'work_mem'
+      - reset_wm.changed == true
+      - reset_wm.restart_required == false
+  when: ansible_distribution == "Ubuntu" and ansible_distribution_major_version == '16'
+
+- name: postgresql_set - reset work_mem again to check that nothing changed (restart is not required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    reset: yes
+  register: reset_wm2
+  ignore_errors: yes
+
+- assert:
+    that:
+      - reset_wm2.name == 'work_mem'
+      - reset_wm2.changed == false
+      - reset_wm2.value_pretty == reset_wm2.prev_val_pretty
+      - reset_wm2.restart_required == false
+  when: ansible_distribution != "Ubuntu" and ansible_distribution_major_version != '16'
+
+- assert:
+    that:
+      - reset_wm2.name == 'work_mem'
+      - reset_wm2.changed == false
+      - reset_wm2.restart_required == false
+  when: ansible_distribution == "Ubuntu" and ansible_distribution_major_version == '16'
+
+- name: postgresql_set - preparation to the next step
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    value: 14MB
+  ignore_errors: yes
+
+- name: postgresql_set - set work_mem to initial state (restart is not required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: work_mem
+    value: default
+  register: def_wm
+  ignore_errors: yes
+
+- assert:
+    that:
+      - def_wm.name == 'work_mem'
+      - def_wm.changed == true
+      - def_wm.value_pretty != def_wm.prev_val_pretty
+      - def_wm.restart_required == false
+      - def_wm.value.value != '14680064' 
+  when: ansible_distribution != "Ubuntu" and ansible_distribution_major_version != '16' and ansible_distribution != 'FreeBSD'
+
+- assert:
+    that:
+      - def_wm.name == 'work_mem'
+      - def_wm.changed == true
+      - def_wm.restart_required == false
+  when: ansible_distribution == "Ubuntu" and ansible_distribution_major_version == '16' and ansible_distribution != 'FreeBSD'
+
+- name: postgresql_set - set shared_buffers (restart is required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: shared_buffers
+    value: 111MB
+  register: set_shb
+  ignore_errors: yes
+
+- assert:
+    that:
+      - set_shb.name == 'shared_buffers'
+      - set_shb.changed == true
+      - set_shb.restart_required == true
+
+# We don't check value.utin because it is none
+- name: postgresql_set - set autovacuum (enabled by default, restart is not required)
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: autovacuum
+    value: off
+  register: set_aut
+  ignore_errors: yes
+
+- assert:
+    that:
+      - set_aut.name == 'autovacuum'
+      - set_aut.changed == true
+      - set_aut.restart_required == false
+      - set_aut.value.value == 'off'
+
+# Test check_mode, step 1. At the previous test we set autovacuum = 'off'
+- name: postgresql - try to change autovacuum again in check_mode
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: autovacuum
+    value: on
+  register: set_aut
+  ignore_errors: yes
+  check_mode: yes
+
+- assert:
+    that:
+      - set_aut.name == 'autovacuum'
+      - set_aut.changed == true
+      - set_aut.restart_required == false
+      - set_aut.value.value == 'off'
+
+# Test check_mode, step 2
+- name: postgresql - check that autovacuum wasn't actually changed after change in check_mode
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: autovacuum
+    value: off
+  register: set_aut
+  ignore_errors: yes
+  check_mode: yes
+
+- assert:
+    that:
+      - set_aut.name == 'autovacuum'
+      - set_aut.changed == false
+      - set_aut.restart_required == false
+      - set_aut.value.value == 'off'
+
+# Test check_mode, step 3. It is different from the prev test - it runs without check_mode: yes
+# Before the check_mode tests autovacuum was off
+- name: postgresql - check that autovacuum wasn't actually changed after change in check_mode
+  become_user: "{{ pg_user }}"
+  become: yes
+  postgresql_set:
+    db: postgres
+    login_user: "{{ pg_user }}"
+    name: autovacuum
+    value: off
+  register: set_aut
+  ignore_errors: yes
+
+- assert:
+    that:
+      - set_aut.name == 'autovacuum'
+      - set_aut.changed == false
+      - set_aut.restart_required == false
+      - set_aut.value.value == 'off'