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Understanding Send Latency
Understanding Send Latency

The overall latency of the Send(Message) method includes all latencies of all operations inside this method. The following sequence of operations is performed when the Send(Message) method is called:

  • Invocation of the OutboundSessionMsgEvent or OutboundApplicationMsgEvent event (for Message objects only).
  • Serialization of the outbound message to the raw buffer. The latency of this action depends on the message class you use. For the Message class, it is an expensive operation and it can take a few microseconds what depends on the message size. For the FlatMessage class it is a very cheap operation, because an object of this class represents actually the serialized buffer.
  • Writing necessary data (message content, timestamp, sequence numbers, etc.) to the session storage. For the File-Based Session Storage, it is a very expensive operation and it can take tens of microseconds. For the Asynchronous File-Based Session Storage, it is far cheaper, because the actual writing is performed in a separate thread. And lastly, for the Memory-based Session Storage, it is a very cheap operation, because data is stored in the memory, not in the file system. Please note, that if the LogBeforeSending option is false, then the logging is performed after sending, please see the corresponding article of the Low Latency Best Practices page for details.
  • Invocation of the MessageSending event.
  • Invocation of the system send function of the TCP socket. In practice, the latency of the system send function can be about 5-10 microseconds what depends on the size of send data, network workload, network software/hardware, etc.
  • If the system send function fails, then the serialized raw buffer is stored in the sending queue for the next process in the sending thread.
Based on the above, one can understand what the send latency includes. However, there is another important aspect. The latency of the Send(Message) method (as any other function) depends on the period with which you call it. When you call a function infrequently, in this case, the function path and associated data structures will not be in a processor cache and this can increase the function latency. However, if you call a function frequently then you can avoid cache misses and keep the function path fast. For this purpose, there is the WarmUp(FlatMessage) method, please see the Low Latency Best Practices page for details.