Siebel: MaxTasks, MaxMTServers, MinMTServers

The values of these 3 Application Object Manager component parameters are set to guide the performance of the Application.
Setting the values of these 3 parameters determine how good the system behaves during user load.
These parameters control the capacity of each server and indirectly control the performance of the whole enterprise.


MaxTasks (Maximum Tasks): This Specifies the total number concurrent threads/tasks that can be run by the Application Object Manager (AOM). Beyond this limit, the AOM will not process any new requests or it will not create any new tasks/threads.

MaxMTServers (Maximum MT Servers): The AOM is a multithreaded process and this parameter specifies the maximum number of multithreaded processes that can concurrently run on this AOM.
After the threshold limit is reached, no more multithreaded processes are generated on the AOM.

MinMTServers (Minumum MT Servers): This parameter specifies the default number of multithreaded processes that are started on the AOM when the parent process is started.The parent AOM process can be started manually from server manager or automatically when the Siebel server starts. The AOM can be disabled by setting this parameter to '0'.
As more number of users start to login to the application, new MT processes are started to serve the additional tasks until the threshold of MaxMTServers is reached.

• Ideally both MaxMTServers and MinMTServers are set to the same value. Doing this will avoid the performance impact to the user, whose login creates a new MT Process. MaxMTServers value should be greater than or equal to MinMTServers.
• The ratio of MaxTasks/MaxMTServers defines the Maximum number of tasks each MT Process can handle.

Let us try to better understand with an example:

If MaxTasks = '300' and MaxMTServers = '3', then MaxTasks/MaxMTServers= 100. This means each MT Server can handle 100 tasks each on the AOM.
Ideally we set both MinMTServer and MaxMTServers to the same value. But let us assume the MinMTServers is set to '2'.
In this case:

• When the Application Object Manager is started, it starts 2 multithreaded processes which can serve 200 tasks/threads.
• As the number of users logging in rises but remain below 200, they are all processed by the 2 MT processes. The requests are distributed evenly between the 2 processes. This is Intra server load balancing which is done by the SC Broker.
• If the number of tasks/threads reach 200 and then a new user request is received, then Siebel starts a new MT process to serve the 201th request. Now, the AOM distributes the tasks among the 3 MT processes.
• If the AOM reaches 300 tasks/threads and a new request comes in, then the AOM cannot handle the request and is termed as "maxed out".

Formulas for calculating the parameter values

• MaxTasks = total_number_users + anon_users
• MaxMTServers = MaxTasks/100
• MinMTServers <= MaxMTServers

The value of 100 in the MaxMTServers formula is taken as a rule of thumb for the AOM.

For special OM's like the eCommunications OM and eProduct Configurator OM, the value is generally 20.

total_number_users is the total number of users the AOM will support.

anon_users is the number of anonymous browser users. HI applications does not support anon users.

for SI application, it would be around 25% of the total_number_users.