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From AJ>
Subject Consistency Levels and Replication with Down Nodes
Date Fri, 10 Jun 2011 18:09:03 GMT
The O'Reilly book on Cass says this about READ consistency level ALL:

"Query all nodes. Wait for all nodes to respond, and return to the 
client the record with the most recent timestamp. Then, if necessary, 
perfrom a read repair in the background.  If any nodes fail or respond, 
fail the read operation."

It says "all nodes".  Shouldn't it say "replication_factor nodes"?  The 
above is implying that if a node, that doesn't even have a copy of the 
row, is down, then the read will fail.  Is that true?

Here is a related question regarding the WRITE consistency level ALL.  
The book says:

"Ensure that the number of nodes specified by replication_factor 
received the write before returning to the client.  If even one replica 
is unresponsive to the write operation, fail the operation."

I can understand this if the given row already exists from a previous 
write and one of the nodes that contains a replica is down.  But, what 
if this is the FIRST time creating this row and one of the nodes that it 
determines should store one of the replicas is down?  Will it choose 
another node to store the replica, or will it use hints to update the 
chosen down node when it comes back up?

Generally speaking for any RF value and for the FIRST write of a 
particular row, does Cass select specific nodes to contain the replicas 
regardless of their availability, and use hints if some of them are 
unavailable?  Or, will it select another available node?


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