[zeromq-dev] Bad ZMQ latency on first 500 messages per connection

Pieter Hintjens ph at imatix.com
Tue Sep 29 09:44:19 CEST 2015


Have you excluded the cost of establishing the TCP connection itself
(something around 10 msec, depending on the setup)?

On Tue, Sep 29, 2015 at 8:49 AM, Ben Kloosterman <bklooste at gmail.com> wrote:
> "As can be seen, sender and receiver throughput's differ at the beginning of
> the test. This seems to suggest that there is some kind of buffering
> involved on the lower layers of the stack"
>
> Nagle is turned off  but it looks like it keeps increasing some sort of
> buffer in the tcp stack.. could also be OS / memory ( page allocation)  /
> Scheduling priority.
>
> Note in those 500 messages the sender was sending a lot more messages , than
> the receiver was receiving so a buffer would be growing somewhere.
>
> Ben
>
> On Tue, Sep 29, 2015 at 4:35 PM, <Christian.Kohrt at rohde-schwarz.com> wrote:
>>
>> Hi all,
>>
>> when sending many messages at once there is a known latency issue: The
>> first 500 messages are sent with a high latency shown in the graph in the
>> whitepaper http://zeromq.org/whitepapers:measuring-performance before it
>> gets to very high speed messaging.
>>
>> The author summarizes:
>> * For latency: ... the latency for first 500 messages is quite poor (up to
>> 1,500 microseconds), however, afterwards it stabilises at approximately 150
>> microseconds, with occasional peaks up to 400 microseconds.
>> * For throughput: This seems to suggest that there is some kind of
>> buffering involved on the lower layers of the stack.
>>
>> In our scenario, we use a Dealer/Router connection, which is in fact like
>> REQ/REP.
>>
>> Question:
>> Why have the first 500 messages this latency issue? What is the reason for
>> this and how could we solve this issue, because we require a high
>> performance application even for the first messages.
>>
>
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