As described in Section 2.5, “Changelog”, all events are written to the ChangeLog table of the database. The table is never truncated by default in order to enable event replay right from the beginning. Nevertheless, you might want to reduce the size of the evergrowing table on your own. In one go, you can also truncate the LinkChangeLog and ObservedValueChangelog tables. That is, because the sequenceno in these tables is a foreign key to the sequenceno in the ChangeLog table and therefore useless if you delete the respective row in the ChangeLog table.

Caution

If you delete events from the ChangeLog, listeners which try to retrieve these events will fail. In particular, Replication Live Server that have not caught up with the Master Live Server will become unusable.

Prerequisites

If you want to truncate the ChangeLog table the following prerequisites should be fulfilled:

Truncate the ChangeLog

When you truncate the ChangeLog, you should not delete all entries. You may leave 100000 entries which is a good value proven by practice. Proceed as follows:

select max(sequenceno) from ChangeLog

delete from ChangeLog where sequenceno < <LimitSequenceNo>

delete from LinkChangeLog where sequenceno < <LimitSequenceNo>

delete from ObservedValueChangeLog where sequenceno < <LimitSequenceNo>

All but the last 100000 entries are deleted from the ChangeLog, LinkChangeLog and ObservedValueChangeLog tables.