rdelval commented on a change in pull request #37: Staggered (Variable batch) Updates URL: https://github.com/apache/aurora/pull/37#discussion_r221124930
########## File path: src/main/java/org/apache/aurora/scheduler/updater/strategy/VariableBatchStrategy.java ########## @@ -0,0 +1,152 @@ +/** + * Licensed 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.aurora.scheduler.updater.strategy; + +import java.util.List; +import java.util.Objects; +import java.util.Optional; +import java.util.Set; +import java.util.stream.Collectors; + +import com.google.common.base.Preconditions; +import com.google.common.collect.ImmutableList; +import com.google.common.collect.ImmutableSet; +import com.google.common.collect.Ordering; + +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * A strategy that limits the number of instances selected by the subclass using variable steps. + * + * @param <T> Instance type. + */ +public class VariableBatchStrategy<T extends Comparable<T>> implements UpdateStrategy<T> { + private final Ordering<T> ordering; + protected final ImmutableList<Integer> maxActiveGroups; + private final boolean rollingForward; + private Optional<Integer> totalModInstanceCount; + + private static final Logger LOG = LoggerFactory.getLogger(VariableBatchStrategy.class); + + /** + * Creates a variable active-limited strategy that applies an upper bound to all results. + * + * @param maxActiveGroups List of Maximum group sizes. Each group size represents a step. + * {@link #getNextGroup(Set, Set)}. + */ + public VariableBatchStrategy(Ordering<T> ordering, + List<Integer> maxActiveGroups, + boolean rollingForward) { + + this.ordering = Objects.requireNonNull(ordering); + this.rollingForward = rollingForward; + + maxActiveGroups.forEach(x -> Preconditions.checkArgument(x > 0)); + + this.maxActiveGroups = ImmutableList.copyOf(maxActiveGroups); + this.totalModInstanceCount = Optional.empty(); + } + + // Determine how far we're into the update based upon how many instances are waiting + // to be modified. + private int determineCurGroupSize(int remaining) { + + // Calculate which groupIndex we are in by finding out how many instances we have left to update + int modified = totalModInstanceCount.get() - remaining; + + int lastGroupSize = maxActiveGroups.get(maxActiveGroups.size() - 1); + + LOG.debug("Variable Batch Update progress: {} instances have been modified, " + + "{} instances remain unmodified, and {} overall instances to be modified.", + modified, + remaining, + totalModInstanceCount.get()); + + if (rollingForward) { + + int sum = 0; + for (Integer groupSize : maxActiveGroups) { + sum += groupSize; + + if (sum > modified) { + return groupSize; + } + } + // Return last step when number of instances > sum of all groups + return lastGroupSize; + } else { + + // To perform the update in reverse, we use the number of remaining tasks left to update + // instead of using the number of already modified instances. In a rollback, the remaining + // count represents the number of instances that were already modified while rolling forward + // and need to be reverted. + int curGroupSize = remaining; + + for (Integer groupSize : maxActiveGroups) { + // This handles an in between step. i.e.: updated instances = 4, update groups = [2,3] + // which results in update groups 2 and 2 rolling forward at the time of failure. + if (curGroupSize <= groupSize) { + return curGroupSize; + } + + curGroupSize -= groupSize; + } + + // Handle the case where number of instances update were + // greater than the sum of all update groups + // Calculate the size of the last update group size performed while rolling forward. + curGroupSize = curGroupSize % lastGroupSize; + if (curGroupSize == 0) { + return lastGroupSize; + } else { + return curGroupSize; + } + } + } + + @Override + public final Set<T> getNextGroup(Set<T> idle, Set<T> active) { + + // Get the size for the idle set on the first run only. This is representative of the number Review comment: This was one of my biggest concerns as well. From actually running the code I found the `totalModInstanceCount` always remains the same value. Our update mechanism is a bit tough to grok but if I'm understanding it correctly, it seems like every time you encounter an update, the whole process is played out from beginning to end. This, combined with the fact that when you try apply an update to an already updated instance results in a noop, makes for a nice catch all process where we can avoid worrying about corner cases (how do we recover our state without writing it to the storage). Same applies to a recovery. So in the end you always end up with that first idle group being the total amount of instances you will modify by the end of the update. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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