mridulm commented on code in PR #2119:
URL:
https://github.com/apache/incubator-celeborn/pull/2119#discussion_r1412853580
##########
master/src/main/scala/org/apache/celeborn/service/deploy/master/Master.scala:
##########
@@ -666,23 +666,32 @@ private[celeborn] class Master(
val shuffleKey = Utils.makeShuffleKey(requestSlots.applicationId,
requestSlots.shuffleId)
val availableWorkers = workersAvailable()
+ // reply false if all workers are unavailable
+ if (availableWorkers.isEmpty) {
+ logError(
+ s"Non available workers, offer slots for $numReducers reducers of
$shuffleKey failed!")
+ context.reply(RequestSlotsResponse(StatusCode.SLOT_NOT_AVAILABLE, new
WorkerResource()))
+ return
+ }
+
val numAvailableWorkers = availableWorkers.size()
val numWorkers = Math.min(
Math.max(
if (requestSlots.shouldReplicate) 2 else 1,
if (requestSlots.maxWorkers <= 0) slotsAssignMaxWorkers
else Math.min(slotsAssignMaxWorkers, requestSlots.maxWorkers)),
numAvailableWorkers)
+
+ // We treated availableWorkers as a Circular Queue here.
val startIndex = Random.nextInt(numAvailableWorkers)
+ val endIndex = startIndex + numWorkers
+
val selectedWorkers = new util.ArrayList[WorkerInfo](numWorkers)
- selectedWorkers.addAll(availableWorkers.subList(
- startIndex,
- Math.min(numAvailableWorkers, startIndex + numWorkers)))
- if (startIndex + numWorkers > numAvailableWorkers) {
- selectedWorkers.addAll(availableWorkers.subList(
- 0,
- startIndex + numWorkers - numAvailableWorkers))
+ for (index <- startIndex until endIndex) {
+ val realIndex = index % numAvailableWorkers
+ selectedWorkers.add(availableWorkers.get(realIndex))
}
+
Review Comment:
Even with the change to `ArrayList`, from `LinkedList`, it is still 1.8x
faster (see [1]).
The readability is not that much different between both versions -
particularly with better comments and less dense code. Not to mention, there is
a clear perf difference.
[1]
Result "com.example.benchmarks.SublistBenchmark.sublistTest":
1017.635 ±(99.9%) 7.152 ns/op [Average]
(min, avg, max) = (1004.876, 1017.635, 1037.149), stdev = 9.548
CI (99.9%): [1010.483, 1024.787] (assumes normal distribution)
Result "com.example.benchmarks.SublistBenchmark.indexTest":
1868.689 ±(99.9%) 32.588 ns/op [Average]
(min, avg, max) = (1819.288, 1868.689, 1955.872), stdev = 43.505
CI (99.9%): [1836.101, 1901.278] (assumes normal distribution)
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