[jira] [Updated] (BEAM-217) BoundedSource.splitAtFraction should be splitAfterFraction

["Kenneth Knowles (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/BEAM-217?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Kenneth Knowles updated BEAM-217:
---------------------------------
    Fix Version/s: First stable release

> BoundedSource.splitAtFraction should be splitAfterFraction
> ----------------------------------------------------------
>
>                 Key: BEAM-217
>                 URL: https://issues.apache.org/jira/browse/BEAM-217
>             Project: Beam
>          Issue Type: Improvement
>          Components: sdk-java-core
>            Reporter: Eugene Kirpichov
>            Assignee: Eugene Kirpichov
>            Priority: Minor
>              Labels: backward-incompatible
>             Fix For: First stable release
>
>
> Dynamic work rebalancing works by 1) determining how long the bundle should take in order to not be a straggler - the "deadline", 2) predicting where the bundle will be (position or fraction) by that deadline, and 3) requesting an atomic split (splitAtFraction).
> Currently all BoundedSource's and (in Dataflow runner) NativeReaderIterator's refuse splits if they have already consumed the requested split position.
> Splitting a task [A, C) at position B generates [A, B) and [B, C), so if we predict that by deadline the task will have last consumed position X, we should split not "at" X, but "after" X (i.e. at next(X)) - i.e. into [A, X] (because X is already consumed) and (X, C) equivalently [A, next(X)) and [next(X), C).
> One way to fit this into the current BoundedSource API is to rename splitAtFraction to splitAfterFraction and adjust the documentation. Documentation of getFractionConsumed also needs to be clarified to emphasize that it should return what fraction of all positions in the source have already been consumed, including the position of the last consumed record. For example, for an index-range task with range [0, 5), after it has read the first record at position 0, it has consumed 20%, rather than 0% (and of course not 40% even if an internal "next index" variable is now 1 - this mistake is especially easy to make in a file-based source if you base the calculations on the file's offset *after* consuming the record - the correct way is to calculate based on offsets of beginning of records).



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