Traces of operations¶
All operations performed by E-Maj, and that impact in any way a tables group, are traced into a table named emaj_hist.
The emaj_hist table structure is the following:
| Column | Type | Description |
|---|---|---|
| hist_id | BIGSERIAL | serial number identifying a row in this history table |
| hist_datetime | TIMESTAMPTZ | recording date and time of the row |
| hist_function | TEXT | function associated to the traced event |
| hist_event | TEXT | kind of event |
| hist_object | TEXT | object related to the event (group, table or sequence) |
| hist_wording | TEXT | additional comments |
| hist_user | TEXT | role whose action has generated the event |
| hist_txid | BIGINT | identifier of the transaction that has generated the event |
The hist_function column can take the following values:
| Value | Meaning |
|---|---|
| ALTER_GROUP | tables group change |
| ALTER_GROUPS | tables groups change |
| CLEANUP_RLBK_STATE | cleanup the state of recently completed rollback operations |
| COMMENT_GROUP | comment set on a group |
| COMMENT_MARK_GROUP | comment set on a mark for a tables group |
| CONSOLIDATE_RLBK_GROUP | consolidate a logged rollback operation |
| CREATE_GROUP | tables group creation |
| DBLINK_OPEN_CNX | open a dblink connection for a rollback operation |
| DBLINK_CLOSE_CNX | close a dblink connection for a rollback operation |
| DELETE_MARK_GROUP | mark deletion for a tables group |
| DISABLE_EVENT_TRIGGERS | desactivate event triggers |
| DROP_GROUP | tables group suppression |
| EMAJ_INSTALL | E-Maj installation or version update |
| ENABLE_EVENT_TRIGGERS | activate event triggers |
| FORCE_DROP_GROUP | tables group forced suppression |
| FORCE_STOP_GROUP | tables group forced stop |
| GEN_SQL_GROUP | generation of a psql script to replay updates for a tables group |
| GEN_SQL_GROUPS | generation of a psql script to replay updates for several tables groups |
| LOCK_GROUP | lock set on tables of a group |
| LOCK_GROUPS | lock set on tables of several groups |
| LOCK_SESSION | lock set on tables for a rollback session |
| PROTECT_GROUP | set a protection against rollbacks on a group |
| PROTECT_MARK_GROUP | set a protection against rollbacks on a mark for a group |
| PURGE_HISTORY | delete from the emaj_hist table the events prior the retention delay |
| RENAME_MARK_GROUP | mark rename for a tables group |
| RESET_GROUP | log tables content reset for a group |
| ROLLBACK_GROUP | rollback updates for a tables group |
| ROLLBACK_GROUPS | rollback updates for several tables groups |
| ROLLBACK_SEQUENCE | rollback one sequence |
| ROLLBACK_TABLE | rollback updates for one table |
| SET_MARK_GROUP | mark set on a tables group |
| SET_MARK_GROUPS | mark set on several tables groups |
| SNAP_GROUP | snap all tables and sequences for a group |
| SNAP_LOG_GROUP | snap all log tables for a group |
| START_GROUP | tables group start |
| START_GROUPS | tables groups start |
| STOP_GROUP | tables group stop |
| STOP_GROUPS | tables groups stop |
| UNPROTECT_GROUP | remove a protection against rollbacks on a group |
| UNPROTECT_MARK_GROUP | remove a protection against rollbacks on a mark for a group |
The hist_event column can take the following values:
| Value | Meaning |
|---|---|
| BEGIN | |
| END | |
| EVENT TRIGGERS DISABLED | |
| EVENT TRIGGERS ENABLED | |
| MARK DELETED | |
| SCHEMA CREATED | secondary schema created |
| SCHEMA DROPPED | secondary schema dropped |
| LOG SCHEMA CHANGED | |
| NAMES PREFIX CHANGED | E-Maj names prefix modified |
| LOG DATA TABLESPACE CHANGED | Tablespace for the log table modified |
| LOG INDEX TABLESPACE CHANGED | Tablespace for the log index modified |
The emaj_hist content can be viewed by anyone who has the proper access rights on this table (superuser, emaj_adm or emaj_viewer roles).
Two other internal tables keep traces of groups alter or rollback operations:
- emaj_alter_plan lists the elementary steps performed during the execution of emaj_alter_group() and related functions,
- emaj_rlbk_plan lists the elementary steps performed during the execution of emaj_rollback_group() and related functions.
When a tables group is started, using the emaj_start_group() function, or when old marks are deleted, using the emaj_delete_before_mark_group() function, the oldest events are deleted from emaj_hist tables. The events kept are those not older than a parametrised retention delay and not older than the oldest active mark and not older than the oldest uncompleted rollback operation. By default, the retention delay for events equals 1 year. But this value can be modified at any time by inserting the history_retention parameter into the emaj_param table with a SQL statement. The same retention applies to the tables that log elementary steps of tables groups alter or rollback operations.