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From Edmond Lau <edm...@ooyala.com>
Subject repeated timeouts on quorum reads
Date Tue, 20 Oct 2009 00:30:42 GMT
Whenever I try to do a quorum read on a row with a particularly large
supercolumn with get_slice under high load, cassandra throws timeouts.
 The reads for that row repeatedly fail until load decreases, but
smaller reads still succeed during that time.  bin/nodeprobe info
shows that the read latency for the column family spikes to up 6-8
seconds.  I've run into this issue since I started to play with
cassandra, but thought that it might go away with beefier nodes.  I've
since gotten more powerful machines, but the timeouts still happen.

Some details:
- cassandra 0.4.1
- 5 nodes, each with 12-core 800MHz with 8GB RAM, 5GB heap size
- replication factor of 3
- RandomPartitioner
- row that fails has a supercolumn with ~30K subcolumns, ~500 bytes
per cell, ~15MB total
- my failed quorum read lists 500 columns to read in the get_slice
call, but the same happens even when I read 100.

The nodes either timeout with 0 or 1 responses (2 of 3 required for a
quorum read):

ERROR [pool-1-thread-24] 2009-10-20 00:07:43,851 Cassandra.java (line
679) Internal error processing get_slice
java.lang.RuntimeException: java.util.concurrent.TimeoutException:
Operation timed out - received only 0 responses from  .
        at org.apache.cassandra.service.CassandraServer.readColumnFamily(CassandraServer.java:108)
        at org.apache.cassandra.service.CassandraServer.getSlice(CassandraServer.java:182)
        at org.apache.cassandra.service.CassandraServer.multigetSliceInternal(CassandraServer.java:251)
        at org.apache.cassandra.service.CassandraServer.get_slice(CassandraServer.java:220)
        at org.apache.cassandra.service.Cassandra$Processor$get_slice.process(Cassandra.java:671)
        at org.apache.cassandra.service.Cassandra$Processor.process(Cassandra.java:627)
        at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:253)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.util.concurrent.TimeoutException: Operation timed out
- received only 0 responses from  .
        at org.apache.cassandra.service.QuorumResponseHandler.get(QuorumResponseHandler.java:88)
        at org.apache.cassandra.service.StorageProxy.strongRead(StorageProxy.java:395)
        at org.apache.cassandra.service.StorageProxy.readProtocol(StorageProxy.java:317)
        at org.apache.cassandra.service.CassandraServer.readColumnFamily(CassandraServer.java:100)
        ... 9 more

ERROR [pool-1-thread-32] 2009-10-19 23:47:21,045 Cassandra.java (line
679) Internal error processing get_slice
java.lang.RuntimeException: java.util.concurrent.TimeoutException:
Operation timed out - received only 1 responses from
172.16.129.75:7000 .
        at org.apache.cassandra.service.CassandraServer.readColumnFamily(CassandraServer.java:108)
        at org.apache.cassandra.service.CassandraServer.getSlice(CassandraServer.java:182)
        at org.apache.cassandra.service.CassandraServer.multigetSliceInternal(CassandraServer.java:251)
        at org.apache.cassandra.service.CassandraServer.get_slice(CassandraServer.java:220)
        at org.apache.cassandra.service.Cassandra$Processor$get_slice.process(Cassandra.java:671)
        at org.apache.cassandra.service.Cassandra$Processor.process(Cassandra.java:627)
        at org.apache.thrift.server.TThreadPoolServer$WorkerProcess.run(TThreadPoolServer.java:253)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:619)
Caused by: java.util.concurrent.TimeoutException: Operation timed out
- received only 1 responses from 172.16.129.75:7000 .
        at org.apache.cassandra.service.QuorumResponseHandler.get(QuorumResponseHandler.java:88)
        at org.apache.cassandra.service.StorageProxy.strongRead(StorageProxy.java:395)
        at org.apache.cassandra.service.StorageProxy.readProtocol(StorageProxy.java:317)
        at org.apache.cassandra.service.CassandraServer.readColumnFamily(CassandraServer.java:100)
        ... 9 more

Any ideas what the issue might be?

Edmond

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