Github user squito commented on the pull request:
https://github.com/apache/spark/pull/6935#issuecomment-161864325
Hi @steveloughran I've done one *rough* pass over the code, thanks for
working on this. This definitely looks promising, the unit tests seem pretty
good so its great that those are passing. It does seem surprisingly
complicated -- I pointed a few confusing places, I know you're still working on
it, perhaps some cleanup will improve things.
On some higher-level things: in an earlier comment you mentioned:
> This probe may need to handle incomplete data; the event log listener
does do a {{flush()}} on major events âthat is not enough to guarantee that
changes are visible across HDFS readers (more precisely, there are no
guarantees if/when writes to a file are picked up by existing input streams;
they may get an out of date view of the data, or an inconsistent one). Because
the input stream is re-opened on the playback, the risk is low âbut is it
there?
I don't understand the danger here. `FsHistoryProvider.replay` always
creates a new InputStream, so it doesn't seem like there is anything to worry
about?
On https://github.com/apache/spark/pull/6545 you mentioned the idea of
having an incremental replay:
> There's one more option to consider here. Why do we actually
replay-then-pause in-progress applications? Why not have a thread continually
loading them and forwarding events until they complete? In this mode, there's
no need to reload the cache, replay events....the UI just stays up to date.
That sounds like a fantastic idea -- but I assume that ended up being much
more complicated in the end?
Also, there are a bunch of style violations that I didn't nitpick on yet --
I just put a few comments in for now.
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