dhepner@hpisod2.HP.COM (Dan Hepner) (03/17/90)
From: shekita@provolone.cs.wisc.edu (E Shekita) >[ .. due to concerns of bus saturation ..] Over the long run, I think >shared-nothing configurations (like Tandem offers) will prevail for >transaction processing systems. Since Tandem distributes the database over its processors, it seems a little exaggerated to describe them as "shared-nothing". Substantial communication requirements exist between those processors to effect not only remote disk IO but also concurrency control and distributed transaction commit. Shared memory systems have a similar problem to solve, of course, but it's reduced by the lack of a remote disk access requirement. All interesting multi-processor OLTP systems end up with shared concurrency and transaction control. Thus for Shekita's claim to be true, one must believe either that: 1) The communication requirements to achieve multi-processor IO, concurrency, and transactions are low enough to not dictate the decision. or 2) Using external communication paths results in superior overall performance regardless of the communication requirement. How likely is either to be true? Some other possibilities: 1) Being bus bandwidth bound is no more difficult to address than other potential bottlenecks in an OLTP system. 2) Alternatives to the bus bottleneck are no less likely to themselves be bottlenecks. Dan Hepner