Github user andrewor14 commented on a diff in the pull request:
https://github.com/apache/spark/pull/1106#discussion_r17331144
--- Diff: core/src/main/scala/org/apache/spark/deploy/master/Master.scala
---
@@ -481,13 +481,26 @@ private[spark] class Master(
if (state != RecoveryState.ALIVE) { return }
// First schedule drivers, they take strict precedence over
applications
- val shuffledWorkers = Random.shuffle(workers) // Randomization helps
balance drivers
- for (worker <- shuffledWorkers if worker.state == WorkerState.ALIVE) {
- for (driver <- List(waitingDrivers: _*)) { // iterate over a copy of
waitingDrivers
+ // Randomization helps balance drivers
+ val shuffledAliveWorkers = Random.shuffle(workers.toSeq.filter(_.state
== WorkerState.ALIVE))
+ val aliveWorkerNum = shuffledAliveWorkers.size
+ var curPos = 0
+ for (driver <- List(waitingDrivers: _*)) { // iterate over a copy of
waitingDrivers
+ // For each waiting driver we pick a worker that has enough
resources to launch it.
+ // The picking does in a round-robin fashion, starting from position
behind last
+ // worker on which driver was just launched and ending with driver
being launched
+ // or we have iterated over all workers.
+ val startPos = curPos
+ curPos = (curPos + 1) % aliveWorkerNum
+ var launched = false
+ while (curPos - 1 != startPos && !launched) {
--- End diff --
Somewhat minor, but why don't we just declare `val startPos = curPos` after
we increment it? Then we don't need the -1 here
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