Traces of operations
The emaj_hist table
All operations performed by E-Maj, and that impact in any way a tables group, are traced into a table named emaj_hist.
Any user having emaj_adm or emaj_viewer rights may look at the emaj_hist content.
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 |
|---|---|
ADJUST_GROUP_PROPERTIES |
ajust the group_has_waiting_changes column content of the emaj_group table |
ASSIGN_SEQUENCE |
sequence assigned to a tables group |
ASSIGN_SEQUENCES |
sequences assigned to a tables group |
ASSIGN_TABLE |
table assigned to a tables group |
ASSIGN_TABLES |
tables assigned to a tables group |
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 |
COMMENT_ROLLBACK |
comment set on an E-Maj rollback |
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_PROTECTION |
desactivate event triggers |
DROP_GROUP |
tables group suppression |
EMAJ_INSTALL |
E-Maj installation or version update |
ENABLE_PROTECTION |
activate event triggers |
EXPORT_GROUPS |
export a tables groups configuration |
EXPORT_PARAMETERS |
export an E-maj parameters configuration |
FORCE_DROP_GROUP |
tables group forced suppression |
FORCE_STOP_GROUP |
tables group forced stop |
FORGET_GROUP |
erase historical traces for a dropped tables group |
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 |
IMPORT_GROUPS |
import a tables groups configuration |
IMPORT_PARAMETERS |
import an E-maj parameters configuration |
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 |
MODIFY_TABLE |
table properties change |
MODIFY_TABLES |
tables properties change |
MOVE_SEQUENCE |
sequence moved to another tables group |
MOVE_SEQUENCES |
sequences moved to another tables group |
MOVE_TABLE |
table moved to another tables group |
MOVE_TABLES |
tables moved to another tables group |
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_HISTORIES |
delete from the historical tables the events prior the retention delay |
REMOVE_SEQUENCE |
sequence removed from its tables group |
REMOVE_SEQUENCES |
sequences removed from their tables group |
REMOVE_TABLE |
table removed from its tables group |
REMOVE_TABLES |
tables removed from their tables group |
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 |
|
DELETED PARAMETER |
parameter deleted from emaj_param |
END |
|
EVENT TRIGGER RECREATED |
|
EVENT TRIGGERS DISABLED |
|
EVENT TRIGGERS ENABLED |
|
GROUP CREATED |
new tables group created |
INSERTED PARAMETER |
parameter inserted into emaj_param |
LOG DATA TABLESPACE CHANGED |
tablespace for the log table modified |
LOG INDEX TABLESPACE CHANGED |
tablespace for the log index modified |
LOG_SCHEMA CREATED |
secondary schema created |
LOG_SCHEMA DROPPED |
secondary schema dropped |
MARK DELETED |
|
NAMES PREFIX CHANGED |
E-Maj names prefix modified |
NOTICE |
warning message issued by a rollback |
PRIORITY CHANGED |
priority level modified |
SEQUENCE ADDED |
sequence added to a logging tables group |
SEQUENCE MOVED |
sequence moved from one group to another |
SEQUENCE REMOVED |
sequence removed from a logging tables group |
TABLE ADDED |
table added to a logging tables group |
TABLE MOVED |
table moved from one group to another |
TABLE REMOVED |
table removed from a logging tables group |
TABLE REPAIRED |
table repaired for E-Maj |
TIME STAMP SET |
internal time stamp recorded |
TRIGGERS TO IGNORE CHANGED |
set of application triggers to ignore at rollback time changed |
UPDATED PARAMETER |
parameter updated in emaj_param |
WARNING |
warning message issued by a rollback |
Other history tables
Several other internal tables store historical data :
emaj_version_hist keeps the trace of the extension version changes;
emaj_group_hist records tables groups creations and drops;
emaj_rel_hist keeps tables and sequences assignments to tables groups;
emaj_log_session records the periods of time when the tables groups are enabled (started);
and several other tables handling E-Maj rollbacks data.
The Emaj_web client is the easiest way to examine these tables content.
Purge obsolete traces
When a tables group is started with reset (emaj_start_group() function), or when old marks are deleted (emaj_delete_before_mark_group() function), the oldest events are deleted from most historical tables. The events kept are those not older than:
a parametrised retention delay,
the oldest mark,
and 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. If the history_retention parameter is set to 100 years or more, no histories purge is executed.
The obsolete traces purge can also be initiated by explicitely calling the emaj_purge_histories() function. The input parameter of the function defines a retention delay that overloads the history_retention parameter of the emaj_param table.
In order to schedule purges periodically, it is possible to:
set the history_retention parameter to a very high value (for instance ‘100 YEARS’)
and schedule purge operations by any mean (crontab, pgAgent, pgTimeTable or any other tool).