add ability to override tuning calculated values

On servers with low ram or custom footprint, it may be useful to manualy
set specific config values like shared_memory and let the tuning role
set other values automaticaly.

roles/tuning/README.md

@@ -31,6 +31,20 @@ The rest of the variables can be configured and are available in the:
   * [roles/tuning/vars/PG.yml](./vars/PG.yml)
 
 
+### `pg_conf_override_tuning`
+
+Defines if the `pg_postgres_conf_params` should override the `tuning`
+values automaticaly calculated from gathered memory informations.
+Default: `false`
+
+Example:
+```yaml
+pg_conf_override_tuning: "true"
+pg_postgres_conf_params:
+- name: shared_buffers
+  value: "128MB"
+```
+
 ### `tuned_profile`
 
 This is the `tuned` profile name used for configuring the system. Default: `edb`

roles/tuning/defaults/main.yml

@@ -2,6 +2,7 @@
 
 pg_instance_name: main
 pg_version: 14
+pg_conf_override_tuning: false
 tuned_profile: "edb"
 tuned_configuration_dir: "/etc/tuned"
 ssd_disk: false

roles/tuning/tasks/tune_postgres.yml

@@ -71,17 +71,38 @@
     _pg_max_connections: >-
       {{ [_sys_nvcpus | int * 4, 100] | max }}
 
-# Set the shared buffers value
+# Override the max_connections value with pg_postgres_conf_params
+- name: Override the variable _pg_max_connections
+  ansible.builtin.set_fact:
+    _pg_max_connections: >-
+      {{ pg_postgres_conf_params |selectattr('name', 'equalto', 'max_connections') |map(attribute='value') |default([_pg_max_connections], true) |first }}
+  when: pg_conf_override_tuning
+
+# Set the shared_buffers value
 - name: Set the variable _pg_shared_buffers_mb
   ansible.builtin.include_tasks: tune_pg_shared_buffers.yml
 
+# Override the shared_buffers value with pg_postgres_conf_params
+- name: Override the variable _pg_shared_buffers_mb
+  ansible.builtin.set_fact:
+    _pg_shared_buffers_mb: >-
+      {{ pg_postgres_conf_params |selectattr('name', 'equalto', 'shared_buffers') |map(attribute='value') |default([_pg_shared_buffers_mb], true) |first |ansible.builtin.regex_replace('mb', '', ignorecase=True) }}
+  when: pg_conf_override_tuning
+
 # Set the work_mem value to: ((Total RAM - shared_buffers)/(16 x CPU cores))
 - name: Set the variable _pg_work_mem_mb
   ansible.builtin.set_fact:
     _pg_work_mem_mb: >-
       {{ ((_sys_memtotal_mb | int - _pg_shared_buffers_mb | int) / (16 * _sys_nvcpus | int)) | round | int }}
 
-# Set the maintenance_work_mem_mb value to:
+# Override the work_mem value with pg_postgres_conf_params
+- name: Override the variable _pg_work_mem_mb
+  ansible.builtin.set_fact:
+    _pg_work_mem_mb: >-
+      {{ pg_postgres_conf_params |selectattr('name', 'equalto', 'work_mem') |map(attribute='value') |default([_pg_work_mem_mb], true) |first |ansible.builtin.regex_replace('mb', '', ignorecase=True) }}
+  when: pg_conf_override_tuning
+
+# Set the maintenance_work_mem value to:
 # MAX(15% x (Total RAM - shared_buffers) / autovacuum_max_workers, 1GB)
 - name: Set the variable _pg_maintenance_work_mem_mb
   ansible.builtin.set_fact:
@@ -96,6 +117,13 @@
         ] | min
       }}
 
+# Override the maintenance_work_mem value with pg_postgres_conf_params
+- name: Override the variable _pg_maintenance_work_mem_mb
+  ansible.builtin.set_fact:
+    _pg_maintenance_work_mem_mb: >-
+      {{ pg_postgres_conf_params |selectattr('name', 'equalto', 'maintenance_work_mem') |map(attribute='value') |default([_pg_maintenance_work_mem_mb], true) |first |ansible.builtin.regex_replace('mb', '', ignorecase=True) }}
+  when: pg_conf_override_tuning
+
 - name: Initialize the Postgres parameters list
   ansible.builtin.set_fact:
     _pg_postgres_conf_params: