The Stored Process Server "Cost Algorithm" determines how requests are
distributed among the Stored Process Servers and how many simultaneous
requests can be accommodated by each Stored Process Server in the
load-balancing cluster.

An overview of the Cost Algorithm for the Stored Process Server is
available at:

   http://support.sas.com/rnd/itech/doc9/admin_oma/sasserver/poollb/
     loadalg.html

Here are some additional notes about the Cost Algorithm.

   1.) The cost is maintained separately for each Stored Process Server.
       For example, if the "Maximum Cost" setting is "1000" and you
       have three Stored Process Servers (i.e. MultiBridge connections)
       then each of these three servers permits a "Maximum Cost" of
       "1000".

   2.) If you are using the default configuration of three Stored
       Process Servers (i.e. three MultiBridge connections) with a
       "Maximum Cost" of "1000", a "Cost Per Client" of "100",
       (and a "context" cost of "100" and a "session" cost of "1")
       then:

       A. Each request generally incurs a total cost of 201
          (100 "Cost Per Client" + 100 "context cost" + 1 "session
          cost" = 201).

       NOTE: The cost per request could, in some cases, be
             less than 201 since the cost for "client", "context"
             and "session" are added at different times.
             If the requests are processed faster than the contexts
             are created, then more than 4 requests could be
             executed simultaneously.  But, for simplicity this
             discussion will assume a cost a total cost of 201 for
             each request.

       B. So, each Stored Process Server can accommodate up to
          four simultaneous requests ( 4 * 201 = 804).  Since 804 is
          less than 1000 (The "Maximum Cost"), but 1005 ( 5 * 201 =
          1005) exceeds the "Maximum Cost", this means that up to four
          simultaneous requests can be accommodated.

       C. Since each Stored Process Server can accommodate up to
          four simultaneous requests, then all three Stored Process
          Servers can accommodate up to twelve simultaneous requests
          ( 4 * 3 = 12 ).

       D. The notes in the Object Spawner log about "updating cost
          with xxx" pertain to the cost of an individual Stored
          Process Server (for example, the Stored Process Server that
          is running on port 8611).  But, the message unfortunately
          does not indicate which specific Stored Process Server is
          getting the cost update.  For example, consider the message:

             Server A5N68MWJ.AW000002 has updating cost with 202

          In this example "A5N68MWJ.AW000002" is the "Logical Stored
          Process Server"  The message does not tell which physical
          Stored Process Server (there are three servers by default)
          received the cost update.

          There are generally "Server xxxxx has client entering" (or
          "Server xxxxx has client leaving" ) messages prior to this
          message that can help determine the specific physical Stored
          Process Server that is associated with the "updating cost with
          xxx" message.

       E. If the logical Stored Process Server (which includes the three
          physical Stored Process Servers) has reached maximum capacity
          at 12 Stored Processes, the Object Spawner will hold any
          pending requests until one server finishes a Stored Process.
          If no server is available in the length of time specified by
          the "Availability Timeout" (the default value is 60 seconds),
          the pending request will be rejected and an ERROR message
          will appear (see "Item 4" below) in your Object Spawner log
          file.

   3.) The total server cost increases by 1 for each active Stored
       Process "session" on the server.  This is generally a minor
       issue, but "sessions" are factored into the Cost Algorithm to
       improve the distribution of work between servers. For more
       information about "Sessions" see:

http://support.sas.com/rnd/itech/doc9/dev_guide/stprocess/sessions.html

   4.) If your Stored Process Servers are experiencing a heavy workload,
       you may see the "updating cost" values increasing in your Object
       Spawner log file as more and more requests are processed.  If
       the cost reaches the "Maximum Cost" value on all of your Stored
       Process Servers, then you will generally see ERROR messages in
       your Object Spawner log file about:

       ERROR: The Balance algorithm timed out before a server could be
              found.

   5.) If you expect to run many simultaneous Stored Processes or you
       have requests rejected because no server is available, you
       should consider adding more MultiBridge connections (i.e., more
       Stored Process Server instances) and/or increasing the
       "Availability Timeout" value for your Stored Process Server.
       Raising the Maximum Cost is not generally recommended unless you
       understand the memory requirements that change may place on
       the Server.

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