Configuration for Large Numbers of Users 

Use the following settings for the maximum configuration of the SAP Web dispatcher.

You need SAP Web Dispatcher version 6.20.14 or 640.40.2 You can see the version in the Web administration interface (see Monitoring the SAP Web Dispatcher). The version corresponds to kernel patch level 1475 (6.20) or 15 (6.40).

Then you can set the parameters in the Web dispatcher profile as follows, for example: 

icm/max_conn            = 8192 icm/max_sockets            = 16384 wdisp/HTTP/max_pooled_con  = 8192 or wdisp/HTTPS/max_pooled_con = 8192 icm/req_queue_len          = 6000 icm/min_threads            = 100 icm/max_threads            = 200 mpi/total_size_MB          = 500 mpi/buffer_size            = 32768 mpi/max_pipes              = 21000

Note that each active HTTP connection needs two sockets as well as two memory pipes (four event flags). (For this reason icm/max_sockets must be double the size of icm/max_conn.) This does not tell us anything about the possible number of simultaneous active users, since, depending on the application, a user can open several HTTP connections at the same time.  You may also have to change operating system parameters for certain high load scenarios. For more information see SAP note 715400.

Relationship Between Users and Active HTTP Connections

To evaluate how many users the SAP Web dispatcher can serve, you must take the following factors into account:

·        When a user sends a request, this request can open more than one HTTP connection. Depending on the application a request can open between one and 10 or 20 HTTP connections. The user cannot see how many connections the request opens. The average number of HTTP connections per request is indicated in the following formula req_per_dialog_step.

·        The “think time” is also crucial to the capacity of the Web dispatcher. The think time is the time (in seconds) between two user dialog steps (clicks). During this time there is no active HTTP connection (depending on the timeout – see below). The think time is indicated in the formula  thinktime_per_diastep_sec.

·        Another important parameter is the keepalive timeout (icm/server_port_<xx> or icm/keep_alive_timeout), which specifies how long the Web dispatcher keeps the connection open for further inquiries from the request. This timeout is specified in seconds in the formula, conn_keepalive_sec.

There is therefore no one fixed formula, since the number of actual parallel HTTP connections, concurrent_conn, depends on all these parameters. This formula can be used as a rule of thumb:

 

The value you set in parameter icm/max_conn must be at least the size as the required number of parallel connections (concurrent_conn in the formula; 8000 in the example below).

To find out the total MPI size mpi/total_size_MB use the formula:

 

You have 12000 users, who use the SAP Web dispatcher to send their requests. On average, each request opens four HTTP connections, the keep-alive timeout is 5 seconds (when the Web dispatcher notices resources are getting low, it automatically reduces the timeout for new connections). The average time between two dialog steps is 30 seconds.

In this example the number of parallel HTTP connections is:

 

The size of the MPIs can then be calculated as follows (if the default setting of 65536 for mpi/buffer_size is halved):

 

Do not set it less than 32 K, since the HTTP header must always have enough space in it.

This also works with the maximum settings shown above.