Paul Gilmartin wrote:
Wouldn't FTP use the same SSI calls as SDSF, with similar performance?
Possibly not. FTP is designed only to read beginning to end. SDSF is designed to allow scrolling up and down, locating specific records, backward find processing, etc.
Keep in mind that SDSF spool access has *always* been comparatively slow. I'm pretty sure they used to use the IAZSPLIO service (SSI 71) to read spool blocks. At some point, I believe they switched everything over to using the spool data set browse (SDSB) facility to facilitate their JES neutrality solution (aka support for JES3). If so, that might have pushed them past the knee of the performance curve. The difference is probably not that noticeable for most smaller data sets.
(E)JES uses a STARTIO I/O driver and modern CCW commands to read whole spool tracks in a single operation, even while our code executes on a zIIP processor. Some of the other, non-IBM spool browsers might also use similar high-performance I/O techniques.
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