Connector output buffers

An output buffer size must be configured for each connector.

The output buffer size configured for a connector must be at least as large as the largest message that is expected to be sent to any client connecting through that connector. However, the buffer size can be much larger so that the messages can be batched at the server, which improves performance.

Each connected client is assigned a socket buffer of the specified size if possible. A warning is logged if a smaller socket buffer was allocated than requested.

In addition each client multiplexer has a buffer of the configured size (as a multiplexer writes to only one of its clients at any one time). The multiplexer buffer is used to batch messages from the client queue before writing and, if the socket buffer does end up being smaller than the configured buffer and the throughput is high, the allocated socket buffer size might become a bottleneck.

Getting the correct output buffer size is vital. Make this too small and the Diffusion server does not batch and write messages to clients at optimal rates. Make them too big, extra memory is consumed or messages might time out and cause the client connection to be closed.

If the output buffer size is larger than the TCP output buffer size, this can cause problems if the client is slow consuming. If a slow-consuming client does not clear messages from the TCP buffer fast enough, messages on the connector buffer which are waiting to move to the TCP output buffer can time out. You can avoid this problem by setting the TCP output buffers for your operating system and the connector output buffers for your Diffusion server to the same value. You can also increase your message timeout interval.

Client output buffers

As at the server, the output buffer sizes in use must be configured for a client.

In the Java™ client this is specified in the ServerDetails object used to make the connection. As the Java client does not buffer messages, this only has to be large enough to cater for the largest message size that is sent to the server.

Connector input buffers

Each connector also specifies an input buffer size.

Input buffers receive messages from clients. This buffer must be as large as the largest message expected. If you specify an input buffer size that is less than the maximum message size, the maximum message size is used as the input buffer size.

This size is also used to allocate a receive socket buffer for the client. The socket buffer allocated might actually be less than requested in which case a warning is logged.

For maximum performance, the size used for this buffer must match up with the output buffer size used by clients.

Client input buffers

Clients must also specify the buffer size to use for input.

In the Java client this is specified in the ServerDetails object used to make the connection.

Matching buffer sizes

For optimal throughput it is desirable to match the size of buffers at each end of every connection. The input buffer size used by clients ideally matches the output buffer size at the connector that they connect to. Also the output buffer size specified by clients must match the input buffer size of the connector they connect to.

Message batching

Each client multiplexer assigns an output buffer of each size specified by client connectors. So if there were 3 client connectors, each specifying a different output buffer size, and 2 client multiplexers, each multiplexer assigns 3 different buffers (6 in total).

When a client multiplexer is unable to write the contents of an output buffer to a client in one go, the writing is deferred and the multiplexer takes a copy of the remaining data in the output buffer into its own temporary buffer.