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From Yudong Gao <st...@umich.edu>
Subject Update the Keyspace replication factor online
Date Tue, 12 Apr 2011 19:56:04 GMT
Hi,

What operations will be executed (and what is the associated overhead)
when the Keyspace replication factor is changed online, in a
multi-datacenter setup with NetworkTopologyStrategy?

I checked the wiki and the archive of the mailing list and find this,
but it is not very complete.

http://wiki.apache.org/cassandra/Operations
"
Replication factor is not really intended to be changed in a live
cluster either, but increasing it may be done if you (a) use
ConsistencyLevel.QUORUM or ALL (depending on your existing replication
factor) to make sure that a replica that actually has the data is
consulted, (b) are willing to accept downtime while anti-entropy
repair runs (see below), or (c) are willing to live with some clients
potentially being told no data exists if they read from the new
replica location(s) until repair is done.
"

More specifically, in this scenario:

{DC1:1, DC2:1} -> {DC2:1, DC3:1}

1. Can this be done online without shutting down the cluster? I
thought there is an "update keyspace" command in the cassandra-cli.

2. If so, what operations will be executed? Will new replicas be
created in new locations (in DC3) and existing replicas be deleted in
old locations (in DC1)?

3. Or they will be updated only with read with ConssitencyLevel.QUORUM
or All, or "nodetool repair"?

Thanks!

Yudong

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