Github user chandnisingh commented on a diff in the pull request:
https://github.com/apache/incubator-apex-malhar/pull/145#discussion_r53717920
--- Diff:
library/src/main/java/com/datatorrent/lib/state/managed/TimeBucketAssigner.java
---
@@ -0,0 +1,223 @@
+/**
+ * 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 com.datatorrent.lib.state.managed;
+
+import java.util.Calendar;
+import java.util.Set;
+
+import javax.validation.constraints.NotNull;
+
+import org.joda.time.Duration;
+
+import com.esotericsoftware.kryo.serializers.FieldSerializer;
+import com.esotericsoftware.kryo.serializers.JavaSerializer;
+import com.google.common.collect.Sets;
+
+import com.datatorrent.api.Component;
+import com.datatorrent.api.Context;
+import com.datatorrent.lib.appdata.query.WindowBoundedService;
+
+/**
+ * Keeps track of time buckets.<br/>
+ *
+ * The data of a bucket is further divided into time-buckets. This
component controls the length of time buckets,
+ * which time-bucket an event falls into and sliding the time boundaries.
+ * <p/>
+ *
+ * The configuration {@link #expireBefore} and {@link #bucketSpan} are
used to calculate number of time-buckets.
+ * For eg. if <code>expireBefore = 1 hour</code> and <code>bucketSpan = 30
minutes</code>, then <code>
+ * numBuckets = 60 minutes/ 30 minutes = 2 </code>.
+ * <p/>
+ *
+ * The time boundaries- start and end, periodically move by span of a
single time-bucket. Any event with time < start
+ * is expired. These boundaries slide between application window by
another thread and not the operator thread.
+ */
+public class TimeBucketAssigner implements
Component<Context.OperatorContext>
+{
+ @NotNull
+ @FieldSerializer.Bind(JavaSerializer.class)
+ private Duration expireBefore = Duration.standardDays(2);
+
+ @FieldSerializer.Bind(JavaSerializer.class)
+ private Duration bucketSpan;
+
+ private long bucketSpanMillis;
+
+ private long fixedStartTime;
+ private long startTime;
+ private long endTime;
+ private int numBuckets;
+
+ private boolean initialized;
+
+ private transient WindowBoundedService windowBoundedService;
+
+ @NotNull
+ private final transient Set<Listener> listeners = Sets.newHashSet();
+
+ private final transient Runnable expiryTask = new Runnable()
+ {
+ @Override
+ public void run()
+ {
+ synchronized (lock) {
+ startTime += bucketSpanMillis;
+ endTime += bucketSpanMillis;
+ for (Listener listener : listeners) {
+ listener.purgeTimeBucketsBefore(startTime);
+ }
+ }
+ }
+ };
+
+ private final transient Object lock = new Object();
+
+ @Override
+ public void setup(Context.OperatorContext context)
+ {
+ if (!initialized) {
+ if (bucketSpan == null) {
+ bucketSpan =
Duration.millis(context.getValue(Context.OperatorContext.APPLICATION_WINDOW_COUNT)
*
+
context.getValue(Context.DAGContext.STREAMING_WINDOW_SIZE_MILLIS));
+ }
+ Calendar calendar = Calendar.getInstance();
+ long now = calendar.getTimeInMillis();
+ fixedStartTime = now - expireBefore.getMillis();
+ startTime = fixedStartTime;
+
+ bucketSpanMillis = bucketSpan.getMillis();
+ numBuckets = (int)((expireBefore.getMillis() + bucketSpanMillis - 1)
/ bucketSpanMillis);
+ endTime = startTime + (numBuckets * bucketSpanMillis);
+
+ initialized = true;
+ }
+ windowBoundedService = new WindowBoundedService(bucketSpanMillis,
expiryTask);
+ windowBoundedService.setup(context);
+ }
+
+ public void beginWindow(long l)
+ {
+ windowBoundedService.beginWindow(l);
+ }
+
+ public void endWindow()
+ {
+ windowBoundedService.endWindow();
+ }
+
+ /**
+ * Get the bucket key for the long value.
+ *
+ * @param value value from which bucket key is derived.
+ * @return -1 if value is already expired; bucket key otherwise.
+ */
+ public long getTimeBucketFor(long value)
+ {
+ long lstart;
+ long lend;
+ synchronized (lock) {
+ lstart = startTime;
+ lend = endTime;
+ }
+ if (value < lstart) {
+ return -1;
+ }
+ long diffFromStart = value - fixedStartTime;
+ long key = diffFromStart / bucketSpanMillis;
+ if (value > lend) {
+ long move = ((value - lend) / bucketSpanMillis + 1) *
bucketSpanMillis;
+ synchronized (lock) {
+ startTime = lstart + move;
+ endTime = lend + move;
+ }
--- End diff --
>> Can (value - lend) ever exceed bucketSpanMillis ?
Yes. ```startTime``` is initialized during setup() and ```endTime =
startTime + numBucket*bucketSpan```.
However ```value``` can come from the event. This time in the event can be
ahead of ```endTime``` (we have seen this in a real application). This
triggers the whole boundary to move ahead.
>> Second, it seems like this assignment could overwrite the assignment
made to startTime and endTime by the expiryTask thread in some scenarios, for
example: (a) We copy the values in the first synchronized block above (b) The
expiryTask thread increments values by bucketSpanMillis (c) We overwrite those
values by the values computed here. Is this OK ?
We haven't seen a problem so far with this in BucketManager because the
time in the event is given a priority over expiry task. However here there
maybe an issue because the listener (```BucketsDataManager```) is notified to
purge data before start time.
Will club (a) and (c) in one block
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