Every connection requires two file descriptors—one for the client connection and one for the connection to the Adaptive Server® Enterprise. An additional connection is required to allow the administrative thread to log in. If you are using cached connections, you must also consider the number of cached connections. Sybase recommends that you configure 100 additional file descriptors for overhead such as Open Client/Server™ shared libraries, character set and locale files, and connection monitor (CMON) threads.
For example, to calculate the minimum number of file descriptors needed for 1000 connections with 50 cached connections:1000 * 2 + 1 + 50 + 100 for a total of 2151 file descriptors per process.
If several short-lived applications, such as Web applications, are continuously connecting to OpenSwitch, Sybase recommends that you observe the TIMED_WAIT state through netstat. The default TIMED_WAIT limit is 2MSL (maximum segment lifetime), which is four minutes. The default limit can result in the maximum file descriptors per process being exceeded as the sockets are held until the 2MSL limit is reached. You can either increase the maximum number of file descriptors per process or reduce the 2MSL limit in the TCP configuration.
For instructions on increasing the file descriptor limit or reducing the 2MSL limit in the TCP configuration, see your operating system vendor documentation.
OpenSwitch uses 30 threads for internal functions. Therefore, you should set the maximum threads per process to at least 30 + maximum OpenSwitch users + 20 (for any additional overhead). For example, if you plan to have 1200 connections at any given time, increase the maximum threads per process to at least 1229.
