errose28 commented on code in PR #8498: URL: https://github.com/apache/ozone/pull/8498#discussion_r2216950041
########## hadoop-hdds/common/src/main/java/org/apache/hadoop/hdds/utils/SlidingWindow.java: ########## @@ -0,0 +1,162 @@ +/* + * 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.hadoop.hdds.utils; + +import java.time.Clock; +import java.time.Duration; +import java.util.ArrayDeque; +import java.util.Deque; +import java.util.concurrent.TimeUnit; + +/** + * + * A sliding window implementation that combines time-based expiry with a + * maximum size constraint. The window tracks event timestamps and maintains two + * limits: + * <ul> + * <li>Time-based: Events older than the specified expiry duration are + * automatically removed + * <li>Size-based: The window maintains at most windowSize latest events, removing + * older events when this limit is exceeded + * </ul> + * + * The window is considered full when the number of non-expired events exceeds + * the specified window size. Events are automatically pruned based on both + * their age and the maximum size constraint. + */ +public class SlidingWindow { + private final Object lock = new Object(); + private final int windowSize; + private final Deque<Long> timestamps; + private final long expiryDurationMillis; + private final Clock clock; + + /** + * Default constructor that uses a monotonic clock. + * + * @param windowSize the maximum number of events that are tracked + * @param expiryDuration the duration after which an entry in the window expires + */ + public SlidingWindow(int windowSize, Duration expiryDuration) { + this(windowSize, expiryDuration, new MonotonicClock()); + } + + /** + * Constructor with a custom clock for testing. + * + * @param windowSize the maximum number of events that are tracked + * @param expiryDuration the duration after which an entry in the window expires + * @param clock the clock to use for time measurements + */ + public SlidingWindow(int windowSize, Duration expiryDuration, Clock clock) { + if (windowSize < 0) { + throw new IllegalArgumentException("Window size must be greater than 0"); + } + if (expiryDuration.isNegative() || expiryDuration.isZero()) { + throw new IllegalArgumentException("Expiry duration must be greater than 0"); + } + this.windowSize = windowSize; + this.expiryDurationMillis = expiryDuration.toMillis(); + this.clock = clock; + // We limit the initial queue size to 100 to control the memory usage + this.timestamps = new ArrayDeque<>(Math.min(windowSize + 1, 100)); + } + + public void add() { + synchronized (lock) { + if (isExceeded()) { + timestamps.remove(); + } + + timestamps.add(getCurrentTime()); + } + } + + /** + * Checks if the sliding window has exceeded its maximum size. + * This is useful to track if we have encountered more events than the window's defined limit. + * @return true if the number of tracked timestamps in the sliding window + * exceeds the specified window size, false otherwise. + */ + public boolean isExceeded() { + synchronized (lock) { + removeExpired(); + return timestamps.size() > windowSize; + } + } + + /** + * Returns the current number of events that are tracked within the sliding window. + * This method ensures that expired events are removed before computing the count. + * + * @return the number of valid timestamps currently in the sliding window + */ + public int getNumEvents() { + synchronized (lock) { + removeExpired(); + return timestamps.size(); + } + } Review Comment: We will need this method at least for logging when this is used in [this part](https://github.com/apache/ozone/blob/b574709dd6df95e9aec250769da73969f8706b49/hadoop-hdds/container-service/src/main/java/org/apache/hadoop/ozone/container/common/volume/StorageVolume.java#L714) of the volume checks. It would probably look something like this: ```java if (ioTestSlidingWindow.isExceeded()) { LOG.error("Failed IO test for volume {}: In the last {} greater than {} failures were encountered.", this, ioTestSlidingWindow.getExpiryDuration(), ioTestSlidingWindow.getWindowSize()); } else if (LOG.isDebugEnabled()) { LOG.debug("IO test results for volume {}: In the last {} {}/{} tolerated failures were encountered.", this, ioTestSlidingWindow.getExpiryDuration(), ioTestSlidingWindow.getNumEventsInWindow(), ioTestSlidingWindow.getWindowSize()); } ``` For this use case I think it makes sense to keep the 1 exceeding entry as an internal implementation detail for `isExceeded` and leave the return value of this method capped at the window size. If we want to add a test to look inside the window and make sure it is not silently leaking events beyond `windowSize + 1` we can have both a regular public one capped at the window size and an `@VisibleForTesting` method that returns the actual size. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: issues-unsubscr...@ozone.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org --------------------------------------------------------------------- To unsubscribe, e-mail: issues-unsubscr...@ozone.apache.org For additional commands, e-mail: issues-h...@ozone.apache.org
