Github user mateiz commented on a diff in the pull request:
https://github.com/apache/spark/pull/1165#discussion_r15147430
--- Diff:
core/src/main/scala/org/apache/spark/util/collection/SizeTracker.scala ---
@@ -0,0 +1,105 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.spark.util.collection
+
+import scala.collection.mutable.ArrayBuffer
+
+import org.apache.spark.util.SizeEstimator
+
+/**
+ * A general interface for collections to keep track of their estimated
sizes in bytes.
+ * We sample with a slow exponential back-off using the SizeEstimator to
amortize the time,
+ * as each call to SizeEstimator is somewhat expensive (order of a few
milliseconds).
+ */
+private[spark] trait SizeTracker {
+
+ import SizeTracker._
+
+ /**
+ * Controls the base of the exponential which governs the rate of
sampling.
+ * E.g., a value of 2 would mean we sample at 1, 2, 4, 8, ... elements.
+ */
+ private val SAMPLE_GROWTH_RATE = 1.1
+
+ /** Samples taken since last resetSamples(). Only the last two are kept
for extrapolation. */
+ private val samples = new ArrayBuffer[Sample]
--- End diff --
Since we only use the last two, can we make this another data structure?
You could even make it a Queue. It's kind of confusing to see an ArrayBuffer
but then a comment that only two are used.
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