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Re: Inter-node messaging latency


Inter-node messaging is rewritten using Netty in 4.0. It will be better to test it using that as potential changes will mostly land on top of that. 

On Mon, Nov 26, 2018 at 7:39 AM Yuji Ito <yuji@xxxxxxxxxxxxxxxxx> wrote:
Hi,

I'm investigating LWT performance with C* 3.11.3.
It looks that the performance is bounded by messaging latency when many requests are issued concurrently.

According to the source code, the number of messaging threads per node is only 1 thread for incoming and 1 thread for outbound "small" message to another node.

I guess these threads are frequently interrupted because many threads are executed when many requests are issued.
Especially, I think it affects the LWT performance when many LWT requests which need lots of inter-node messaging are issued.

I measured that latency. It took 2.5 ms in average to enqueue a message at a node and to receive the message at the **same** node with 96 concurrent LWT writes.
Is it normal? I think it is too big latency, though a message was sent to the same node.

Decreasing numbers of other threads like `concurrent_counter_writes`, `concurrent_materialized_view_writes` reduced a bit the latency.
Can I change any other parameter to reduce the latency?
I've tried using message coalescing, but they didn't reduce that.

* Environment
- 3 node cluster
- Replication factor: 3
- Node instance: AWS EC2 i3.xlarge

* C* configuration
- Apache Cassandra 3.11.3
- commitlog_sync: batch
- concurrent_reads: 32 (default)
- concurrent_writes: 32 (default)

Thanks,
Yuji


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