cassandra-commits mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From "Ariel Weisberg (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CASSANDRA-13442) Support a means of strongly consistent replication with storage requirements approximating RF=2
Date Wed, 12 Apr 2017 18:29:41 GMT
Ariel Weisberg created CASSANDRA-13442:
------------------------------------------

             Summary: Support a means of strongly consistent replication with storage requirements
approximating RF=2
                 Key: CASSANDRA-13442
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-13442
             Project: Cassandra
          Issue Type: Improvement
          Components: Compaction, Coordination, Distributed Metadata, Local Write-Read Paths
            Reporter: Ariel Weisberg


Replication factors like RF=2 can't provide strong consistency and availability because if
a single node is lost it's impossible to reach a quorum of replicas. Stepping up to RF=3 will
allow you to lose a node and still achieve quorum for reads and writes, but requires committing
additional storage.

The requirement of a quorum for writes/reads doesn't seem to be something that can be relaxed
without additional constraints on queries, but it seems like it should be possible to relax
the requirement that 3 full copies of the entire data set are kept. What is actually required
is a covering data set for the range and we should be able to achieve a covering data set
and high availability without having three full copies. 

After a repair we know that some subset of the data set is fully replicated. At that point
we don't have to read from a quorum of nodes for the repaired data. It is sufficient to read
from a single node for the repaired data and a quorum of nodes for the unrepaired data.

One way to exploit this would be to have N replicas, say the last N replicas in the preference
list, delete all repaired data after a repair completes. Subsequent quorum reads will be able
to retrieve the repaired data from any of the two full replicas and the unrepaired data from
a quorum read of any replica including the "transient" replicas.



--
This message was sent by Atlassian JIRA
(v6.3.15#6346)

Mime
View raw message