Description of problem:
The storage node uses org.apache.cassandra.auth.CassandraAuthorizer for authorization checks. This imposes a non-trivial amount of overhead because now authorization checks are performed for each read/write request. To mitigate that overhead, a local cache of permissions is stored. The default lifetime for a cache entry is set by the permissions_validity_in_ms property in cassandra.yaml. It defaults to two seconds.

When a node comes under heavy load, I have on several occassions started seeing read timeout exceptions, even on writes. This is because of the authorization check which very frequently has to query the system_auth.permissions table. The exceptions look like in rhq-storage.log look like,

ERROR [Native-Transport-Requests:1101] 2013-10-07 14:06:52,730 ErrorMessage.java (line 210) Unexpected exception during request
com.google.common.util.concurrent.UncheckedExecutionException: java.lang.RuntimeException: org.apache.cassandra.exceptions.ReadTimeoutException: Operation timed out - received only 0 responses.
        at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2258)
        at com.google.common.cache.LocalCache.get(LocalCache.java:3990)
        at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:3994)
        at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4878)
        at org.apache.cassandra.service.ClientState.authorize(ClientState.java:290)
        at org.apache.cassandra.service.ClientState.ensureHasPermission(ClientState.java:170)
        at org.apache.cassandra.service.ClientState.hasAccess(ClientState.java:163)
        at org.apache.cassandra.service.ClientState.hasColumnFamilyAccess(ClientState.java:147)
        at org.apache.cassandra.cql3.statements.ModificationStatement.checkAccess(ModificationStatement.java:67)
        at org.apache.cassandra.cql3.QueryProcessor.processStatement(QueryProcessor.java:100)
        at org.apache.cassandra.cql3.QueryProcessor.processPrepared(QueryProcessor.java:223)
        at org.apache.cassandra.transport.messages.ExecuteMessage.execute(ExecuteMessage.java:121)
        at org.apache.cassandra.transport.Message$Dispatcher.messageReceived(Message.java:287)

I want to make set permissions_validity_in_ms to five minutes which substantially reduces the overhead of the authorization checks but does not allow the permissions to get stale either.

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