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From "Chris Jansen" <chris.jan...@cognitomobile.com>
Subject UnavailableException with 3 nodes and RF=2
Date Tue, 14 Sep 2010 08:43:39 GMT
Hi All,

 

I'm a newbie to Cassandra so I could have a configuration issue here, I
am using the latest stable release 0.6.0.

 

I have created a cluster of 3 nodes, a keyspace with RF=2 and a rack
unaware replication strategy. When I write with CL=QUORUM with all 3
nodes commit the data fine, but when I write with the same CL with one
of the nodes down I see an UnavailableException thrown. Surely if one of
the nodes in the cluster is down another should acknowledge the writes
and maintain the quorum, or is there something that I have
misunderstood? From what I understand, in this case with a RF=2 for the
quorum writes to succeed I need two nodes to acknowledge the write
(RF/2+1), which I have.

 

Here is how the cluster looks when quorum writes succeed:

 

192.168.245.2 Up         477.33 KB
78502309573904554351249603414557542595     |<--|

192.168.245.4 Up         426.74 KB
139625953069891725539207365034742863768    |   |

192.168.245.1 Up         496.67 KB
163572901304139170217093255272499595459    |-->|

 

This is how it looks with one node down and quorum writes fail (I am
writing to 192.168.245.1):

 

192.168.245.2 Down       423.58 KB
78502309573904554351249603414557542595     |<--|

192.168.245.4 Up         426.74 KB
139625953069891725539207365034742863768    |   |

192.168.245.1 Up         496.67 KB
163572901304139170217093255272499595459    |-->|

 

Here is the exception that is thrown:

 

Cannot write: 9e48b039-7687-4b14-9b40-0096b15fd7b0 RETRYING

UnavailableException()

                at
org.apache.cassandra.thrift.Cassandra$insert_result.read(Cassandra.java:
12303)

                at
org.apache.cassandra.thrift.Cassandra$Client.recv_insert(Cassandra.java:
675)

                at
org.apache.cassandra.thrift.Cassandra$Client.insert(Cassandra.java:648)

                at cassandraclient.Main.writeReadDelete(Main.java:101)

                at cassandraclient.Main.run(Main.java:188)

                at java.lang.Thread.run(Thread.java:619)

 

If I switch CL=ONE the writes succeed, but I don't know if the data is
being replicated.

 

Any help would be greatly appreciated, thanks.

 

Chris Jansen



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