(default 15) In incremental and bi-directional snapshot time stamp
of last replayed snapshot log entry (LAST_TS) is kept in system
tables. LAST_TS is used to determine the starting point of the next
update. This value can't be used as is for the following
Local time may be adjusted occasionally on the servers which
participate in replication.
Virtuoso snapshot replication triggers use now() function to get snapshot log entry time
stamp. If transaction is started before updating snapshot log and
ended after updating snapshot log is finished, data modifications
made in this transaction will be missed.
In order to resolve the issues mentioned above Virtuoso reads
snapshot logs starting from LAST_TS minus some tolerance offset.
The value of tolerance offset (in minutes) is kept in
"snp_repl_tolerance_offset" registry variable. For the reasons
mentioned above tolerance offset should be longer than length of
any transaction which modifies published tables.
(default 30) In order to prevent snapshot log entries to be
replayed more than once Virtuoso keeps log of replayed snapshot log
entries (rplog). Rplog entries need to be purged periodically.
Virtuoso automatically schedules rplog purger when snapshot log for
some table is created. All the records in rplog with time stamp
less than MIN(LAST_TS) minus some offset are purged. The value of
purge offset (in minutes) is kept in "snp_repl_purge_offset"
registry variable. Normally, purge offset should be greater than