LocalStrategy means that data is not replicated in the usual way and remains local to each node. Where it is used, replication is either not required (for example in the case of secondary indexes and system.local) or happens out of band via some other method (as in the case of schema, or system.peers which is populated largely from gossip).
There are several components in Cassandra which generate or persist "system" data for which a normal distribution makes sense. Auth data is one, tracing, repair history and materialized view status are others. The keyspaces for this data generally use SimpleStategy by default as it is guaranteed to work out of the box, regardless of topology. The intent of the advice to configure system_auth with RF=N was to increase the likelihood that any read of auth data would be done locally, avoiding remote requests where possible. This is somewhat outdated though and not really necessary. In fact, the 3.x docs actually suggest "3 to 5 nodes per Data Center"[1] FTR, you can't specify LocalStrategy in a CREATE or ALTER KEYSPACE, for these reasons. [1] http://docs.datastax.com/en/cassandra/3.x/cassandra/configuration/secureConfigNativeAuth.htm On Fri, May 13, 2016 at 10:47 AM, Jérôme Mainaud <jer...@mainaud.com> wrote: > Hello, > > Is there any good reason why system_auth strategy is SimpleStrategy by > default instead of LocalStrategy like system and system_schema ? > > Especially when documentation advice to set the replication factor to the > number of nodes in the cluster, which is both weird and inconvenient to > follow. > > Do you think that changing the strategy to LocalStrategy would work or > have undesirable side effects ? > > Thank you. > > -- > Jérôme Mainaud > jer...@mainaud.com >
