gtps4m0gSystem Generation

Interrelationship of Multiprocessing Components

The relationships of loosely coupled multiprocessing (LC), tightly coupled multiprocessing (TC), interprocessor communications (IPC), and the multiple database function (MDBF) are somewhat complex. A comprehension of these relationships is particularly important in order to install a TPF system. Figure 4 is an abstraction of the relationships. Frequently the term abstraction connotes unrealistic, difficult, or obscure. This is not the intent of Figure 4. This abstraction is used to hide many of the details of reality which, if exposed, obscure the principle ideas to comprehend concepts. A familiar expression used to convey this thought is: "You can't see the forest because of the trees." To use a metaphor -- Figure 4 is the TPF forest. If you have been patient enough to reach this point, then the exposures should be helpful in order to unravel the relationships, which are frequently hidden in the trees.

Figure 4 includes 4 CPCs, each with 4 I-streams. Each CPC interconnects through channel-to-channel (CTC) communications, several communication controllers, and a sizeable amount of DASD. The communication lines, which are attached to the communication controllers, are equally distributed to the 4 CPCs. There are 2 subsystems, each with 2 subsystem users. There are 4 applications, 1 for each subsystem user. Consider what happens when 16 messages arrive (at about the same microsecond) at each CPC. Through luck and the statistical smoothing algorithm mentioned in Scheduler Algorithm, each message gets dispatched to each of the 16 I-streams a few nanoseconds apart. Through bad luck each message is quadrupled; for example, the messages that cause Entries to be created for the same applications on each of the CPCs result in 16 FIND and HOLDs to the same record. All records are VFA candidates but none are currently in the cache, which is full. Furthermore, each of the applications makes extensive use of the global area for intra program communication.

Some easy exposures:

  1. The messages could all have been for a single application with 16 messages still dispatched to 16 I-streams, necessary for the 16 FIND and HOLDs to be to the same record.
  2. Are the FIND and HOLDs recommended? Will the system prevent this?
  3. How much interprocessor communications (IPC) traffic will the applications generate among the CPCs?

Figure 4. Interrelationship of Multiprocessing Components