tree aea5869f049353f24c48a62181d0dff2a80bcf39
parent e6c36168147d9c70c07c834acfaad575e08a5bb6
author John Yang <johnyangk@gmail.com> 1534909234 +0900
committer Sanha Lee <sanhaleehana@gmail.com> 1534909234 +0900

[NEMO-179] Delayed Task Cloning (#112)

JIRA: [NEMO-179: Delayed Task Cloning](https://issues.apache.org/jira/projects/NEMO/issues/NEMO-179)

**Major changes:**
- Two options for ClonedSchedulingProperty: Speculative execution(fraction, medianTimeMultiplier) + Upfront cloning
- ScheduledExecutorService in RuntimeMaster: Check for speculative execution every 100ms
- Data structures to identify stragglers and clone tasks in PlanStateManager
- BlockState: No longer transitions from NOT_AVAILABLE to other states (similar to TaskState), assuming that a new Block attempt takes over the failed one 

**Minor changes to note:**
- Fix a bug in SourceLocationAwareSchedulingConstraint, as its getIntermediateDataLocation is no longer deterministic (randomly fetches one of the clone outputs)
- Log when the speculative execution is triggered
- Indentations

**Tests for the changes:**
- Unit test(TaskRetryTest): Tests combinations of Task retry + Task speculation (cloning), both of which lead to new task attempts
- Integration test(WordCountITCase#testSpeculativeExecution): In addition to the existing test for upfront cloning, this tests conditional (very aggressive) speculative cloning.

**Other comments:**
- N/A

Closes #112