how long the scheduler waits before relaxing placement

[Steve Loughran <st...@hortonworks.com>]

In discussion with Vinod, it turns out that YARN only waits (by default) 40 placement cycles before relaxing placement -about 1 second.

That may be good for short-lived apps, where it assumes that locality is for data locality and the hit of remote-data load can be handled, but it seems premature for containers to run long-lived, especially against things like hbase data sets.

Either we get some special placement policy for long-lived apps from a future YARN version, or slider implements the logic itself, something of

1. make strict request
2. if the request is outstanding after a given time, relax it.