This change refactors the portions of the ExecutorAllocationManager class that
track executor state into a new class, to achieve a few goals:
- make the code easier to understand
- better separate concerns (task backlog vs. executor state)
- less synchronization between event and allocation threads
- less coupling between the allocation code and executor state tracking
The executor tracking code was moved to a new class (ExecutorMonitor) that
encapsulates all the logic of tracking what happens to executors and when
they can be timed out. The logic to actually remove the executors remains
in the EAM, since it still requires information that is not tracked by the
new executor monitor code.
In the executor monitor itself, of interest, specifically, is a change in
how cached blocks are tracked; instead of polling the block manager, the
monitor now uses events to track which executors have cached blocks, and
is able to detect also unpersist events and adjust the time when the executor
should be removed accordingly. (That's the bug mentioned in the PR title.)
Because of the refactoring, a few tests in the old EAM test suite were removed,
since they're now covered by the newly added test suite. The EAM suite was
also changed a little bit to not instantiate a SparkContext every time. This
allowed some cleanup, and the tests also run faster.
Tested with new and updated unit tests, and with multiple TPC-DS workloads
running with dynamic allocation on; also some manual tests for the caching
behavior.
Closes#24704 from vanzin/SPARK-20286.
Authored-by: Marcelo Vanzin <vanzin@cloudera.com>
Signed-off-by: Imran Rashid <irashid@cloudera.com>
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