Another reason Elasticsearch is a better primary store is that Snapshots are Consistent at a time point.  This is a natural benefit of Lucene's immutable files.  Cassandra backups are Eventually Consistent and are difficult to restore.  I saw co-workers doing a Cassandra restore; it was not a good day for them.

For complete disaster recovery, restore a Snapshot from time T, then have Logstash consume messages after time T from Kafka.  This will result in reading some messages twice.  If the application assigns document ids (or Logstash computes them from other fields), then indexing requests will just replace a duplicate in Elasticsearch.

If a shard goes Red and can not be restored, this disaster recovery method will work well.

As a distributed primary store for Time-Series Event data, nothing is more solid than Elasticsearch using these techniques.


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