Yes, there's overhead involved in capturing data changes and replicating them. That's true on every platform. I think you're fundamentally asking "How much?" The basic, unsatisfying answer is "It depends. Try it." It depends on the velocity of data changes and the amount of replicated data, fundamentally. To some extent it also depends on how much "data lag" you're willing to tolerate when the systems at either/both ends have better, more important things to do. If you have such inputs, and if they're reliable, then reasonable estimates should be possible.
Before you get too bogged down, though, there's another fundamental question you ought to be asking: "Why cache at all?" I assume the motivation to cache data is that you think you might avoid certain data access workload on the "left" side of the picture. But there's still data access workload on the "right" side of the picture, it's never free, and moving the data from the left side to the right side is also not free. There are also security, data currency, and other considerations. Anyway, briefly setting aside those important other considerations, you ought to try solving this basic equation: Direct Data Access (>, =, or < ?) Capture + Replication + Caching Tier + Cached Data Access Have you calculated the Direct Data Access part of that equation yet? If it's $5 (metaphorically or actually), do you even need any more analysis? It's entirely possible that "one of these things is not like the other," as Sesame Street teaches: https://www.youtube.com/watch?v=6b0ftfKFEJg Sometimes we torture ourselves over analyses that just don't matter. (Is it 5 times or 18 times more expensive for the "Rube Goldberg" solution? Hmmmm, decisions, decisions....) Increasingly we're discovering, or rediscovering, that basic fact. To provide that "Direct Data Access" to VSAM there are several options. Here are a couple notable examples in no particular order: 1. z/OS Connect Version 1.2 (which you probably already have a license to, and which is something like 98% zIIP eligible) or z/OS Connect Enterprise Edition (same comment about zIIP eligibility), presumably via CICS TS or IMS TM, as applicable. 2. Another IBM InfoSphere software product from the catalog, the IBM InfoSphere Classic Federation Server for z/OS, which provides a SQL (JDBC, ODBC, etc.) interface to VSAM data. (It can do more than that, but it certainly does that.) 3. The IBM DB2 Analytics Accelerator with IBM DB2 Analytics Accelerator Loader. This is still a "caching" loop (arguably), but it's an extremely efficient one with security considerations well addressed. -------------------------------------------------------------------------------------------------------- Timothy Sipples IT Architect Executive, Industry Solutions, IBM z Systems, AP/GCG/MEA -------------------------------------------------------------------------------------------------------- E-Mail: [email protected] ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
