measured via JMX console i.e. does not include client-cassandra-client latency
20 client threads 176975b value StorageProxy.WriteLatency ~660ms
10 client threads 176975b value StorageProxy.WriteLatency ~350ms
05 client threads 176975b value StorageProxy.WriteLatency ~156ms
20 client threads 4978b value StorageProxy.WriteLatency ~32ms
10 client threads 4978b value StorageProxy.WriteLatency ~32ms
05 client threads 4978b value StorageProxy.WriteLatency ~31ms
20 client threads 1000b value StorageProxy.WriteLatency ~30ms
10 client threads 1000b value StorageProxy.WriteLatency ~30ms
05 client threads 1000b value StorageProxy.WriteLatency ~29ms
so for a 200KB value you are seeing >200ms of latency in
MessagingService? How much for a 1KB value?
On Mon, Oct 5, 2009 at 1:46 PM, Igor Katkov <email@example.com> wrote:
> In case anyone is following this, here is an update:
> I was able to narrow it down to Cassandra-Cassandra link. Storage proxy
> latency depends on size of the key. The larger amount of data (per key) is
> transfered the larger latency is. No surprise here.
> Client connects to a demons "A" and sends key-value, "A" accept thrift
> message, de-serialize it to an object, sees that key belongs to demons "B",
> serialize it to bytes once again (internal format now) and invoke
> MessagingService, which in turn writes to a socket. As soon as "B" delivers
> write-acknowledgment over a different connection, the client call is let go.
> Cassandra's MessagingService utilizes java nio to connect to other cassandra
> daemons, all connections are uni-directionals. So in theory it should be
> very fast. But it's not.
> What does look suspicious is certain network usage cap, only ~4% of the
> 1Gbps link is used regardless of "value" size. With smaller value I get a
> better throughput, with larger (200Kb) - worse.
> As a temp workaround I see that client might be held responsible to
> identifying what cassandra instance it should send a key to. On 200kb value
> it's ~10 times faster.
> On Thu, Oct 1, 2009 at 6:51 PM, Igor Katkov <firstname.lastname@example.org> wrote:
>> I have the following puzzle:
>> Storage proxy write latency ~235ms
>> CF write latency <1 ms
>> I have 3 nodes in the cluster, Cassandra v.0.4. Tokens evenly distributed.
>> The client connects to a node and inserts a key with ConsistencyLevel.ONE
>> If it happen to be a local write operation is fast, same speed as in one
>> node setup. JMX shows write latency <1 ms
>> If it happens to be a remote insert StorageProxy sends it to a proper
>> node. This operation is slow. JMX shows write latency ~ 235ms.
>> In the same time, on remote node JMX shows same <1ms write latency. So
>> it's not remote node being sluggish, it's something else.
>> There are no pending tasks on remote node - JMX counters are always zero,
>> network is 1Gb, idle. So I can't blame it.
>> I profiled Cassandra server in JProfiler, could not find a thing. All this
>> extra time is spent inside QuorumResponseHandler waiting for the condition
>> to signal. Which should happen as soon as response is received.
>> There is one pooled TCP connection open to remote host. Hardly a
>> bottleneck, ThreadPoolExecutors looks OK.
>> Any ideas why write latency it is so high?