When to Use MSSQ Sets


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Note: Multiple Servers, Single Queue (MSSQ) sets are not supported in BEA Tuxedo CORBA servers.

The MSSQ scheme offers additional load balancing in BEA Tuxedo ATMI environments. One queue is accommodated by several servers offering identical services at all times. If the server queue to which a request is sent is part of an MSSQ set, the message is dequeued to the first available server. Thus load balancing is provided at the individual queue level.

When a server is part of an MSSQ set, it must be configured with its own reply queue. When the server makes requests to other servers, the replies must be returned to the original requesting server; they must not be dequeued by other servers in the MSSQ set.

You can configure MSSQ sets to be dynamic so they automatically spawn and eliminate servers based upon a queue load.

The following table specifies when it is beneficial to use MSSQ sets.

*You Should* Use MSSQ Sets If . . .**	*You Should Not* Use MSSQ Sets If . . .**
You have between 2 and 12 servers.	There are many servers. (A compromise is to use many MSSQ sets.)
Buffer sizes are not too large, that is, large enough to exhaust a queue.	Buffer sizes are large enough to exhaust one queue.
All servers offer identical sets of services.	Each server offers different services.
Messages are relatively small.	Large messages are being passed to the services, causing the queue to be exhausted. When a queue is exhausted, either nonblocking sends fail or blocking sends block.
Optimization and consistency of service turnaround time are paramount.

The following two analogies illustrate when it is beneficial to use MSSQ sets.

A situation analogous to the appropriate use of MSSQ sets can be found in a bank at which several tellers performing identical services handle a single line of customers. The next available teller always takes the next person in line. In this scenario, each teller must be able to perform all customer services. In a BEA Tuxedo environment, all servers set up to share a single queue must offer an identical set of services at all times. The advantage of MSSQ sets is that they offer a second form of load balancing at the individual queue level.
A supermarket at which different cashiers accept different forms of payment (some accept credit cards, while others accept only cash) is similar to a BEA Tuxedo application in which MSSQ sets should not be used.