The E-Maj extension works with some parameters. Those are stored into the emaj_param internal table.
The emaj_param table structure is the following:
| Column | Type | Description |
|---|---|---|
| param_key | TEXT | keyword identifying the parameter |
| param_value_text | TEXT | parameter value, if its type is text (otherwise NULL) |
| param_value_int | INT | parameter value, if its type is integer (otherwise NULL) |
| param_value_boolean | BOOLEAN | parameter value, if its type is boolean (otherwise NULL) |
| param_value_interval | INTERVAL | parameter value, if its type is time interval (otherwise NULL) |
The E-Maj extension installation procedure inserts a single row into the emaj_param table. This row, that should not be modified, describes parameter:
- version : (text) current E-Maj version.
But the E-Maj administrator may insert other rows into the emaj_param table to change the default value of some parameters.
Presented in alphabetic order, the existing key values are:
- alter_log_table : (text) ALTER TABLE directive executed at the log table creation ; no ALTER TABLE exectuted by default (to :ref:`add one or several technical columns<addLogColumns>`).
- avg_fkey_check_duration : (interval) default value = 20 µs ; defines the average duration of a foreign key value check ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- avg_row_delete_log_duration : (interval) default value = 10 µs ; defines the average duration of a log row deletion ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- avg_row_rollback_duration : (interval) default value = 100 µs ; defines the average duration of a row rollback ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- fixed_dblink_rollback_duration : (interval) default value = 4 ms ; defines an additional cost for each rollback step when a dblink connection is used ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- fixed_table_rollback_duration : (interval) default value = 1 ms ; defines a fixed rollback cost for any table belonging to a group ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- fixed_step_rollback_duration : (interval) default value = 2,5 ms ; defines a fixed cost for each rollback step ; can be modified to better represent the performance of the server that hosts the database when using the :ref:`emaj_estimate_rollback_group() <emaj_estimate_rollback_group>` function.
- history_retention : (interval) default value = 1 year ; it can be adjusted to change the retention delay of rows in the :ref:`emaj_hist <emaj_hist>` history table,
Below is an example of a SQL statement that defines a retention delay of history table's rows equal to 3 months:
INSERT INTO emaj.emaj_param (param_key, param_value_interval) VALUES ('history_retention','3 months'::interval);
It is also possible to manage parameter values using any graphic tool such as PgAdmin or phpPgAdmin.
Only superuser and roles having emaj_adm rights can access the emaj_param table.
Roles having emaj_viewer rights can only access a part of the emaj_param table, through the emaj.emaj_visible_param view. This view just masks the real value of the param_value_text column for the 'dblink_user_password' key.