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From Nick Bailey <>
Subject Re: Understanding UnavailableException
Date Fri, 17 Aug 2012 15:00:59 GMT
This blog post should help:

But to answer your question:

>> UnavailableException is bit tricky. It means, that not all replicas
>> required by CL received update. Actually you do not know, whenever update
>> was stored or not, and actually what went wrong.

This is actually incorrect. If you get an UnavailableException, the
write was rejected by the coordinator and was not written anywhere.

>>> a) Suppose we are doing a ConsistencyLevel.ALL write on a 3 node cluster.
>>> My understanding is that if one of the nodes is down and the coordinator
>>> node is aware of that(through gossip), then it will respond to the request
>>> with an UnavailableException. Is this correct?


>>> b) What happens if the coordinator isn't aware of a node being down and
>>> sends the request to all the nodes and never hears back from one of the
>>> node. Would this result in a TimedOutException or a UnavailableException?

You will get a TimedOutException

>>> c) I am trying to understand the cases where the client receives an
>>> error, but data could have been inserted into Cassandra. One such case is
>>> the TimedOutException. Are there any other situations like these?

This should be the only case.

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