If the SMP system supports network affinity migration, each engine handles the network I/O for its connections. During login, Adaptive Server migrates the client connection task from engine 0 to the engine currently servicing the smallest number of connections. The client’s tasks run network I/O on that engine (network affinity) until the connection is terminated. To determine if your SMP system supports this migration, see the configuration documentation for your platform.
By distributing the network I/O among its engines, Adaptive Server can handle more user connections. The per-process limit on the maximum number of open file descriptors no longer limits the number of connections. Adding more engines linearly increases the maximum number of file descriptors, as stored in the global variable @@max_connections.
As you increase the number of engines, Adaptive Server prints the increased @@max_connections value to standard output and the error log file after you restart the server. You can query the value as follows:
select @@max_connections
This number represents the maximum number of file descriptors allowed by the operating system for your process, minus these file descriptors used by Adaptive Server:
One for each master network listener on engine 0 (one for every “master” line in the interfaces file entry for that Adaptive Server)
One for each engine’s standard output
One for each engine’s error log file
Two for each engine’s network affinity migration channel
One per engine for configuration
One per engine for the interfaces file
For example, if Adaptive Server is configured for one engine, and the value of @@max_connections equals 1019, adding a second engine increases the value of @@max_connections to 2039 (assuming only one master network listener).
You can configure the number of user connections parameter to take advantage of an increased @@max_connections limit. However, each time you decrease the number of engines using max online engines, you must also adjust the number of user connections value accordingly. Reconfiguring max online engines or number of user connections is not dynamic, so you must restart the server to change these configuration values. For information about configuring number of user connections, see Chapter 5, “Setting Configuration Parameters.”
