Github user erikerlandson commented on the pull request:
https://github.com/apache/spark/pull/1689#issuecomment-55627362
Hi @rxin,
1) SimpleFutureAction is still referred to in submitJob method, but that
doesn't appear to be invoked anywhere. I was reluctant to get rid of it, as
it's all experimental, and I could envision use cases for it.
2) I see your point. I don't currently have any clever ideas to avoid that
scenario when it happens.
3) Very interesting -- so this scenario is triggered because
`defaultPartitioner` starts examining input RDD partitioners, which sets off
the job when it trips over the data driven partitioning computation from
`sortByKey`.
My impression is that this whack-a-mole with non-laziness stems from a
combination of (a) a data-dependent partitioner(s), with (b) methods that refer
to input partitioners as part of the construction of new RDDs. It *might* be
possible to thread some design changes around so that references to
partitioning are consistently encapsulated in a Future. Functions such as
`defaultPartitioner` would then also have to return a Future, etc. Or, even
more generally, somehow encapsulate *all* RDD initialization in a Future, with
the idea that these futures would finally unwind when some Action was invoked.
However it seems (imo) outside the scope of this particular Jira/PR. Maybe
we could start another umbrella Jira to track possible solutions along these
lines.
Another orthogonal thought -- you can short circuit all this by providing a
partitioner instead of forcing it to be computed from data. That's not as
sexy, or widely applicable, as some deeper fix to the problem, but users can do
it now as a workaround when it's feasible.
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