Pre-install deployment check list
Turn off swap on every Cassandra node.
Open Cassandra ports in firewall.
Configure system limits.
Implement Network Time Protocol
Implement the Dovecot Pro
dictmapfs driver on every Dovecot backend server.
Apache Cassandra is a distributed database with tunable consistency. Normally our Dovecot configuration implements
Quorum provides strong consistency with failure toleration.
replication factor of 3,
quorum is \(2*((sum\_of\_replication/2)+1)\).
This means it is entirely possible for the data to be inconsistent on one node.
nodetool repair is the
AntEntropy service that uses Merkle trees to detect and repair inconsistencies in data between replicas.
Another important element is
10 days by default) which is the tombstone time to live marker.
If a node is missing the tombstone after the
gc_grace_seconds period, the deleted data will be resurrected.
In the Dovecot Pro log file, if you start seeing
Object exists in dict, but not in storage errors, then you most likely have resurrected deleted data.
Resurrected deleted data will have to be manually deleted.
To prevent Cassandra data resurrection, you must regularly run
nodetool repair within
gc_grace_seconds via cron for the entire cluster.