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From Terje Marthinussen <>
Subject balance between concurrent_[reads|writes] and feeding/reading threads i clients
Date Mon, 28 Mar 2011 08:55:05 GMT

I was pondering about how the concurrent_read and write settings balances
towards max read/write threads in clients.

Lets say we have 3 nodes, and concurrent read/write set to 8.
That is, 8*3=24 threads for reading and writing.

Replication factor is 3.

Lets say we have clients that in total set up 16 connections to each node.

Now all the clients write at the same time. Since the replication factor is
3, you could get up to 16*3=48  concurrent write request per node (which
needs to be handled by 8 threads)?

What is the result if this load continues?
Could you see that replication of data fails (at least initially) causing
all kinds of fun timeouts around in the system?

Same on the read side.
If all clients read at the same time with Consistency level QUORUM, you get
16*2 read requests in best case (and more in worst case)?

Could you see that one node answers, but another one times out due to lack
of read threads, causing read repair which again further degrades?

How does this queue up internally between thrift, gossip and the threads
doing the actual read and writes?


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