The V12 Help says "Side effects - None", and while that may be true from a semantic point of view, I know for a fact it is not true from a performance point of view. Also, I believe the effects on performance have evolved from release to release, AND that these effects are probably difficult to describe. But please, someone take a shot (V12 only). Justification: There are reasons, possibly not great reasons but reasons nonetheless, that someone may wish to issue an explicit CHECKPOINT. For example, SELECT count FROM SYSTAB is much faster than SELECT COUNT(*) but the value is only up-to-date after a checkpoint... as are other interesting counters in the system tables. Also, folks might want to know what can happen when an automatic checkpoint occurs... all in one place in the docs (say, where the CHECKPOINT statement is described). |
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Point 7 includes updating max_identity values, right? (And I love the AmigaOS reference - has it ever been a supported platform?) 3
Yes, point 7 includes updating the max_identity values. I'm pretty sure there was never an AmigaOS port of SQLAnywhere. That might be fun -- I wonder what state the tools are in :) I was an Amiga programmer a long time ago and I still have my Amiga 1000 and 3000. I even had the A3000 running a few months ago and though it definitely felt foreign, it was surprising how quickly some of the AmigaDOS insanity came flooding back. Insanity such as "dir #?.c". Yeah, "#?" instead of "*". Strange, but it came back to me. For 'Background checkpoints' (also known 'lazy', 'idle', 'background' or 'overlapping' checkpoints) there is an unlocking/locking step just prior to and after step "10" in the above article: (9.5) Exit exclusive mode (10) Write all dirty pages from cache (10.5) Enter exclusive mode
(28 Jul '11, 11:23)
Jeff Albion
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Who does trigger such background checkpoints - are these the automatic checkpoints the server issues when he thinks it's time to do so - in contrast to checkpoints done explicitly or implicitly by certain statements?
(28 Jul '11, 11:39)
Volker Barth
That is correct.
(28 Jul '11, 13:49)
John Smirnios
So it would mean automatic checkpoints allow tasks to do some work during the "Forbid" phase - by temporarily "unlock the gate"?
(28 Jul '11, 16:45)
Volker Barth
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Not as an answer, but as a connected topic: Cf. http://sqlanywhere-forum.sap.com/questions/683, dealing with the statements that issue an implicit checkpoint. That could be documented together, I guess.