Add section '9. Other considerations for FLU/sequencer implementations'
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@ -392,7 +392,35 @@ Fortunately for Machi, its file data is immutable and therefore can
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easily manage many migrations in parallel, i.e., its submap list may
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be several maps long, each one for an in-progress file migration.
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* 9. Acknowledgments
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* 9. Other considerations for FLU/sequencer implementations
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** Append to existing file when possible
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In the earliest Machi FLU implementation, it was impossible to append
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to the same file after ~30 seconds. For example:
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- Client: ~append(prefix="foo",...) -> {ok,"foo^suffix1",Offset1}~
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- Client: ~append(prefix="foo",...) -> {ok,"foo^suffix1",Offset2}~
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- Client: ~append(prefix="foo",...) -> {ok,"foo^suffix1",Offset3}~
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- Client: sleep 40 seconds
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- Server: after 30 seconds idle time, stop Erlang server process for
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the ~"foo^suffix1"~ file
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- Client: ...wakes up...
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- Client: ~append(prefix="foo",...) -> {ok,"foo^suffix2",Offset4}~
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Our ideal append behavior is to always append to the same file. Why?
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It would be nice if Machi didn't create zillions of tiny files if the
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client appends to some prefix very infrequently. In general, it is
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better to create fewer & bigger files by re-using a Machi file name
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when possible.
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The sequencer should always assign new offsets to the latest/newest
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file for any prefix, as long as all prerequisites are also true,
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- The epoch has not changed. (In AP mode, epoch change -> mandatory file name suffix change.)
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- The latest file for prefix ~p~ is smaller than maximum file size for a FLU's configuration.
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* 10. Acknowledgments
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The source for the "migration-4.png" and "migration-3to4.png" images
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come from the [[http://hibari.github.io/hibari-doc/images/migration-3to4.png][HibariDB documentation]].
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