cmccabe commented on a change in pull request #9901: URL: https://github.com/apache/kafka/pull/9901#discussion_r568030679
########## File path: metadata/src/main/java/org/apache/kafka/timeline/SnapshotRegistry.java ########## @@ -0,0 +1,247 @@ +/* + * 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.kafka.timeline; + +import java.util.ArrayList; +import java.util.HashMap; +import java.util.Iterator; +import java.util.List; +import java.util.stream.Collectors; + +import org.apache.kafka.common.utils.LogContext; +import org.slf4j.Logger; + + +/** + * A registry containing snapshots of timeline data structures. + * We generally expect a small number of snapshots-- perhaps 1 or 2 at a time. + * Therefore, we use ArrayLists here rather than a data structure with higher overhead. + */ +public class SnapshotRegistry { + class SnapshotIterator implements Iterator<Snapshot> { + Snapshot cur; + Snapshot result = null; + + SnapshotIterator(Snapshot start) { + cur = start; + } + + @Override + public boolean hasNext() { + return cur != head; + } + + @Override + public Snapshot next() { + result = cur; + cur = cur.next(); + return result; + } + + @Override + public void remove() { + if (result == null) { + throw new IllegalStateException(); + } + deleteSnapshot(result); + result = null; + } + } + + class ReverseSnapshotIterator implements Iterator<Snapshot> { + Snapshot cur; + + ReverseSnapshotIterator() { + cur = head.prev(); + } + + @Override + public boolean hasNext() { + return cur != head; + } + + @Override + public Snapshot next() { + Snapshot result = cur; + cur = cur.prev(); + return result; + } + } + + private final Logger log; + + /** + * A map from snapshot epochs to snapshot data structures. + */ + private final HashMap<Long, Snapshot> snapshots = new HashMap<>(); + + /** + * The head of a list of snapshots, sorted by epoch. + */ + private final Snapshot head = new Snapshot(Long.MIN_VALUE); + + public SnapshotRegistry(LogContext logContext) { + this.log = logContext.logger(SnapshotRegistry.class); + } + + /** + * Returns a snapshot iterator that iterates from the snapshots with the + * lowest epoch to those with the highest. + */ + public Iterator<Snapshot> iterator() { + return new SnapshotIterator(head.next()); + } + + /** + * Returns a snapshot iterator that iterates from the snapshots with the + * lowest epoch to those with the highest, starting at the snapshot with the + * given epoch. + */ + public Iterator<Snapshot> iterator(long epoch) { + return iterator(getSnapshot(epoch)); + } + + /** + * Returns a snapshot iterator that iterates from the snapshots with the + * lowest epoch to those with the highest, starting at the given snapshot. + */ + public Iterator<Snapshot> iterator(Snapshot snapshot) { + return new SnapshotIterator(snapshot); + } + + /** + * Returns a reverse snapshot iterator that iterates from the snapshots with the + * highest epoch to those with the lowest. + */ + public Iterator<Snapshot> reverseIterator() { + return new ReverseSnapshotIterator(); + } + + /** + * Returns a sorted list of snapshot epochs. + */ + public List<Long> epochsList() { + List<Long> result = new ArrayList<>(); + for (Iterator<Snapshot> iterator = iterator(); iterator.hasNext(); ) { + result.add(iterator.next().epoch()); + } + return result; + } + + /** + * Gets the snapshot for a specific epoch. + */ + public Snapshot getSnapshot(long epoch) { + Snapshot snapshot = snapshots.get(epoch); + if (snapshot == null) { + throw new RuntimeException("No snapshot for epoch " + epoch + ". Snapshot " + + "epochs are: " + epochsList().stream().map(e -> e.toString()). + collect(Collectors.joining(", "))); + } + return snapshot; + } + + /** + * Creates a new snapshot at the given epoch. + * + * @param epoch The epoch to create the snapshot at. The current epoch + * will be advanced to one past this epoch. + */ + public Snapshot createSnapshot(long epoch) { + Snapshot last = head.prev(); + if (last.epoch() >= epoch) { + throw new RuntimeException("Can't create a new snapshot at epoch " + epoch + + " because there is already a snapshot with epoch " + last.epoch()); + } + Snapshot snapshot = new Snapshot(epoch); + last.appendNext(snapshot); + snapshots.put(epoch, snapshot); + log.debug("Creating snapshot {}", epoch); + Snapshot n = head.next(); + while (n != head) { + n = n.next(); + } + return snapshot; + } + + /** + * Reverts the state of all data structures to the state at the given epoch. + * + * @param targetEpoch The epoch of the snapshot to revert to. + */ + public void revertToSnapshot(long targetEpoch) { + Snapshot target = getSnapshot(targetEpoch); + Iterator<Snapshot> iterator = iterator(target); + iterator.next(); + while (iterator.hasNext()) { + Snapshot snapshot = iterator.next(); + log.debug("Deleting snapshot {} because we are reverting to {}", + snapshot.epoch(), targetEpoch); + iterator.remove(); + } + target.handleRevert(); + } + + /** + * Deletes the snapshot with the given epoch. + * + * @param targetEpoch The epoch of the snapshot to delete. + */ + public void deleteSnapshot(long targetEpoch) { + deleteSnapshot(getSnapshot(targetEpoch)); + } + + /** + * Deletes the given snapshot. + * + * @param snapshot The snapshot to delete. + */ + public void deleteSnapshot(Snapshot snapshot) { + Snapshot prev = snapshot.prev(); + if (prev != head) { + prev.mergeFrom(snapshot); Review comment: So the merging logic is needed when deleting a snapshot that isn't the oldest snapshot ---------------------------------------------------------------- This is an automated message from the Apache Git Service. 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