eXtremeDB HA Synchronization procedure

Here is the description of synchronization procedure:

1.masterand Replica databases has a ha_sequencer-64bit integer which is initializedby zero at startup.

2. masterincrements The sequencer at each commit of a WRITE transaction and sends Thesequencer value ALO Ng with transaction data to the replica (s)

3. Ifthe Replica successfully applies the received transaction, it sets Itssequencer to the received Val Ue. So after the transaction is committed, thevalues of the ha_sequencer is the same on the master and replica.

4. whenthe replica connects to the master, it sends the value of Ha_sequencer. Mastercompare its own value with received one. If values is equal, this means thatthe master and replica has the same database version and no synchronization Isrequire D-replica reports mco_repl_notify_db_equal notification code.

5. Otherwise (if master ' s and replica's sequencer values are different), the masterinitiates the Synchron ization procedure depending on the mode_flags-static,hot-sync or stateful initialization.

So, the db_equal code means, the values ofha_sequencers on the master and replica is EQUAL. If the replica ' s database isin-memory and newly created, the replica ' s sequencer is 0. This means, Themaster ' s sequencer is also 0. But this was possible only if the master didn ' tperform write transactions since creation of the database.

eXtremeDB HA Synchronization procedure