gianm commented on code in PR #19559:
URL: https://github.com/apache/druid/pull/19559#discussion_r3359271863
##########
multi-stage-query/src/main/java/org/apache/druid/msq/dart/guice/DartWorkerConfig.java:
##########
@@ -41,6 +44,22 @@ public class DartWorkerConfig
@JsonProperty("heapFraction")
private double heapFraction = DEFAULT_HEAP_FRACTION;
+ /**
+ * Worker-local value for the segment load-ahead count used to size segment
prefetch in {@link ReadableInputQueue}.
+ * <p>
+ * Defaults to null (unset), which leaves the value to query context (client
or controller-default supplied) and the
+ * built-in {@code 2 * threadCount} fallback. When set to a positive value,
it acts as a worker-local floor: the
+ * effective count becomes the larger of this value and any value present in
the query context, so a query can still
Review Comment:
I think it would be better to use the value from the query context as-is, if
it is provided. That way the query context can more easily be used for
experimentation and temporary tuning, in either direction.
##########
multi-stage-query/src/main/java/org/apache/druid/msq/dart/worker/DartWorkerContext.java:
##########
@@ -148,6 +157,9 @@ public class DartWorkerContext implements WorkerContext
final int baseThreadCount = processingConfig.getNumThreads();
final Integer maxThreads =
MultiStageQueryContext.getMaxThreads(queryContext);
this.threadCount = (maxThreads != null && maxThreads > 0) ?
Math.min(baseThreadCount, maxThreads) : baseThreadCount;
+
+ // Worker-local segment load-ahead config, read once from this worker's
DartWorkerConfig.
+ this.segmentLoadAheadCountConfig =
injector.getInstance(DartWorkerConfig.class).getSegmentLoadAheadCount();
Review Comment:
Probably better to not use the injector so explicitly here. It would be more
aligned to do it like the other stuff in this constructor, which is injected
into `DartWorkerContextFactoryImpl` and then passed through.
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