kowshik commented on a change in pull request #10218: URL: https://github.com/apache/kafka/pull/10218#discussion_r610293058
########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogLeaderEpochState.java ########## @@ -0,0 +1,172 @@ +/* + * 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.server.log.remote.metadata.storage; + +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentId; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadata; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.Iterator; +import java.util.Map; +import java.util.NavigableMap; +import java.util.Set; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentSkipListMap; + +/** + * This class represents the in-memory state of segments associated with a leader epoch. This includes the mapping of offset to + * segment ids and unreferenced segments which are not mapped to any offset but they exist in remote storage. + * <p> + * This is used by {@link RemoteLogMetadataCache} to track the segments for each leader epoch. + */ +class RemoteLogLeaderEpochState { + + // It contains offset to segment ids mapping with the segment state as COPY_SEGMENT_FINISHED. + private final NavigableMap<Long, RemoteLogSegmentId> offsetToId = new ConcurrentSkipListMap<>(); + + /** + * It represents unreferenced segments for this leader epoch. It contains the segments still in COPY_SEGMENT_STARTED + * and DELETE_SEGMENT_STARTED state or these have been replaced by callers with other segments having the same + * start offset for the leader epoch. These will be returned by {@link RemoteLogMetadataCache#listAllRemoteLogSegments()} + * and {@link RemoteLogMetadataCache#listRemoteLogSegments(int leaderEpoch)} so that callers can clean them up if + * they still exist. These will be cleaned from the cache once they reach DELETE_SEGMENT_FINISHED state. + */ + private final Set<RemoteLogSegmentId> unreferencedSegmentIds = ConcurrentHashMap.newKeySet(); + + // It represents the highest log offset of the segments that were updated with updateHighestLogOffset. + private volatile Long highestLogOffset; + + /** + * Returns all the segments associated with this leader epoch sorted by start offset in ascending order. + * + * @param idToSegmentMetadata mapping of id to segment metadata. This will be used to get RemoteLogSegmentMetadata + * for an id to be used for sorting. + */ + Iterator<RemoteLogSegmentMetadata> listAllRemoteLogSegments(Map<RemoteLogSegmentId, RemoteLogSegmentMetadata> idToSegmentMetadata) { + // Return all the segments including unreferenced metadata. + int size = offsetToId.size() + unreferencedSegmentIds.size(); + if (size == 0) { + return Collections.emptyIterator(); + } + + ArrayList<RemoteLogSegmentMetadata> metadataList = new ArrayList<>(size); + for (RemoteLogSegmentId id : offsetToId.values()) { + metadataList.add(idToSegmentMetadata.get(id)); Review comment: Hmm here we assume that `id` should be present in the provided `idToSegmentMetadata`. Due to programming error, or other reasons, the caller may not be able to ensure this. Would it be safer if we instead threw whenever `id` is absent in `idToSegmentMetadata` to catch that case? ########## File path: clients/src/test/java/org/apache/kafka/test/TestUtils.java ########## @@ -535,4 +536,46 @@ public static void setFieldValue(Object obj, String fieldName, Object value) thr field.setAccessible(true); field.set(obj, value); } + + /** + * Returns true if both iterators have same elements in the same order. + * + * @param iterator1 first iterator. + * @param iterator2 second iterator. + * @param <T> type of element in the iterators. + */ + public static <T> boolean sameElementsWithOrder(Iterator<T> iterator1, Review comment: Here is a slightly simpler version: ``` while (iterator1.hasNext() && iterator2.hasNext()) { if (!Objects.equals(iterator1.next(), iterator2.next())) { return false; } } return !iterator1.hasNext() && !iterator2.hasNext(); ``` ########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogMetadataCache.java ########## @@ -0,0 +1,309 @@ +/* + * 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.server.log.remote.metadata.storage; + +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentId; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadata; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadataUpdate; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentState; +import org.apache.kafka.server.log.remote.storage.RemoteResourceNotFoundException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.Collections; +import java.util.Iterator; +import java.util.Map; +import java.util.NavigableMap; +import java.util.Objects; +import java.util.Optional; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentMap; + +/** + * This class provides an in-memory cache of remote log segment metadata. This maintains the lineage of segments + * with respect to leader epochs. + * <p> + * Remote log segment can go through the state transitions as mentioned in {@link RemoteLogSegmentState}. + * <p> + * This class will have all the segments which did not reach terminal state viz DELETE_SEGMENT_FINISHED. That means,any + * segment reaching the terminal state will get cleared from this instance. + * This class provides different methods to fetch segment metadata like {@link #remoteLogSegmentMetadata(int, long)}, + * {@link #highestOffsetForEpoch(int)}, {@link #listRemoteLogSegments(int)}, {@link #listAllRemoteLogSegments()}. Those + * methods have different semantics to fetch the segment based on its state. + * <p> + * <ul> + * <li> + * {@link RemoteLogSegmentState#COPY_SEGMENT_STARTED}: + * <br> + * Segment in this state indicates it is not yet copied successfully. So, these segments will not be + * accessible for reads but these are considered for cleanups when a partition is deleted. + * </li> + * <li> + * {@link RemoteLogSegmentState#COPY_SEGMENT_FINISHED}: + * <br> + * Segment in this state indicates it is successfully copied and it is available for reads. So, these segments + * will be accessible for reads. But this should be available for any cleanup activity like deleting segments by the + * caller of this class. + * </li> + * <li> + * {@link RemoteLogSegmentState#DELETE_SEGMENT_STARTED}: + * Segment in this state indicates it is getting deleted. That means, it is not available for reads. But it should be + * available for any cleanup activity like deleting segments by the caller of this class. + * </li> + * <li> + * {@link RemoteLogSegmentState#DELETE_SEGMENT_FINISHED}: + * Segment in this state indicate it is already deleted. That means, it is not available for any activity including + * reads or cleanup activity. This cache will clear entries containing this state. + * </li> + * </ul> + * + * <p> + * The below table summarizes whether the segment with the respective state are available for the given methods. + * <pre> + * +---------------------------------+----------------------+------------------------+-------------------------+-------------------------+ + * | Method / SegmentState | COPY_SEGMENT_STARTED | COPY_SEGMENT_FINISHED | DELETE_SEGMENT_STARTED | DELETE_SEGMENT_STARTED | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | remoteLogSegmentMetadata | No | Yes | No | No | + * | (int leaderEpoch, long offset) | | | | | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | listRemoteLogSegments | Yes | Yes | Yes | No | + * | (int leaderEpoch) | | | | | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | listAllRemoteLogSegments() | Yes | Yes | Yes | No | + * | | | | | | + * +---------------------------------+----------------------+------------------------+-------------------------+-------------------------+ + * </pre> + * </p> + * <p></p> + */ +public class RemoteLogMetadataCache { + + private static final Logger log = LoggerFactory.getLogger(RemoteLogMetadataCache.class); + + // It contains all the segment-id to metadata mappings which did not reach the terminal state viz DELETE_SEGMENT_FINISHED. + private final ConcurrentMap<RemoteLogSegmentId, RemoteLogSegmentMetadata> idToSegmentMetadata + = new ConcurrentHashMap<>(); + + // It contains leader epoch to the respective entry containing the state. + private final ConcurrentMap<Integer, RemoteLogLeaderEpochState> leaderEpochEntries = new ConcurrentHashMap<>(); + + /** + * Returns {@link RemoteLogSegmentMetadata} if it exists for the given leader-epoch containing the offset and with + * {@link RemoteLogSegmentState#COPY_SEGMENT_FINISHED} state, else returns {@link Optional#empty()}. + * + * @param leaderEpoch leader epoch for the given offset + * @param offset offset + * @return the requested remote log segment metadata if it exists. + */ + public Optional<RemoteLogSegmentMetadata> remoteLogSegmentMetadata(int leaderEpoch, long offset) { + RemoteLogLeaderEpochState remoteLogLeaderEpochState = leaderEpochEntries.get(leaderEpoch); + + if (remoteLogLeaderEpochState == null) { + return Optional.empty(); + } + + // Look for floor entry as the given offset may exist in this entry. + RemoteLogSegmentId remoteLogSegmentId = remoteLogLeaderEpochState.floorEntry(offset); + if (remoteLogSegmentId == null) { + // If the offset is lower than the minimum offset available in metadata then return empty. + return Optional.empty(); + } + + RemoteLogSegmentMetadata metadata = idToSegmentMetadata.get(remoteLogSegmentId); + // Check whether the given offset with leaderEpoch exists in this segment. + // Check for epoch's offset boundaries with in this segment. + // 1. Get the next epoch's start offset -1 if exists + // 2. If no next epoch exists, then segment end offset can be considered as epoch's relative end offset. + Map.Entry<Integer, Long> nextEntry = metadata.segmentLeaderEpochs().higherEntry(leaderEpoch); + long epochEndOffset = (nextEntry != null) ? nextEntry.getValue() - 1 : metadata.endOffset(); + + // Return empty when target offset > epoch's end offset. + return offset > epochEndOffset ? Optional.empty() : Optional.of(metadata); + } + + public void updateRemoteLogSegmentMetadata(RemoteLogSegmentMetadataUpdate metadataUpdate) + throws RemoteResourceNotFoundException { + log.debug("Updating remote log segment metadata: [{}]", metadataUpdate); + Objects.requireNonNull(metadataUpdate, "metadataUpdate can not be null"); + + RemoteLogSegmentState targetState = metadataUpdate.state(); + RemoteLogSegmentId remoteLogSegmentId = metadataUpdate.remoteLogSegmentId(); + RemoteLogSegmentMetadata existingMetadata = idToSegmentMetadata.get(remoteLogSegmentId); + if (existingMetadata == null) { + throw new RemoteResourceNotFoundException("No remote log segment metadata found for :" + + remoteLogSegmentId); + } + + // Check the state transition. + checkStateTransition(existingMetadata.state(), targetState); + + switch (targetState) { + case COPY_SEGMENT_STARTED: + // Callers should use addCopyInProgressSegment to add RemoteLogSegmentMetadata with state as + // RemoteLogSegmentState.COPY_SEGMENT_STARTED. + throw new IllegalArgumentException("metadataUpdate: " + metadataUpdate + " with state " + RemoteLogSegmentState.COPY_SEGMENT_STARTED + + " can not be updated"); + case COPY_SEGMENT_FINISHED: + handleSegmentWithCopySegmentFinishedState(metadataUpdate, existingMetadata); + break; + case DELETE_SEGMENT_STARTED: + handleSegmentWithDeleteSegmentStartedState(metadataUpdate, existingMetadata); + break; + case DELETE_SEGMENT_FINISHED: + handleSegmentWithDeleteSegmentFinishedState(metadataUpdate, existingMetadata); + break; + default: + throw new IllegalArgumentException("Metadata with the state" + targetState + " is not supported"); + } + } + + private void handleSegmentWithCopySegmentFinishedState(RemoteLogSegmentMetadataUpdate metadataUpdate, + RemoteLogSegmentMetadata existingMetadata) { + log.debug("Adding remote log segment metadata to leader epoch mappings with update: [{}]", metadataUpdate); + + doHandleSegmentStateTransitionForLeaderEpochs(existingMetadata, + RemoteLogLeaderEpochState::handleSegmentWithCopySegmentFinishedState); + + // Put the entry with the updated metadata. + idToSegmentMetadata.put(existingMetadata.remoteLogSegmentId(), + existingMetadata.createWithUpdates(metadataUpdate)); + } + + private void handleSegmentWithDeleteSegmentStartedState(RemoteLogSegmentMetadataUpdate metadataUpdate, + RemoteLogSegmentMetadata existingMetadata) { + log.debug("Cleaning up the state for : [{}]", metadataUpdate); + + doHandleSegmentStateTransitionForLeaderEpochs(existingMetadata, + RemoteLogLeaderEpochState::handleSegmentWithDeleteSegmentStartedState); + + // Put the entry with the updated metadata. + idToSegmentMetadata.put(existingMetadata.remoteLogSegmentId(), + existingMetadata.createWithUpdates(metadataUpdate)); + } + + private void handleSegmentWithDeleteSegmentFinishedState(RemoteLogSegmentMetadataUpdate metadataUpdate, + RemoteLogSegmentMetadata existingMetadata) { + log.debug("Removing the entry as it reached the terminal state: [{}]", metadataUpdate); + + doHandleSegmentStateTransitionForLeaderEpochs(existingMetadata, + RemoteLogLeaderEpochState::handleSegmentWithDeleteSegmentFinishedState); + + // Remove the segment's id to metadata mapping because this segment is considered as deleted and it cleared all + // the state of this segment in the cache. + idToSegmentMetadata.remove(existingMetadata.remoteLogSegmentId()); + } + + private void doHandleSegmentStateTransitionForLeaderEpochs(RemoteLogSegmentMetadata existingMetadata, + RemoteLogLeaderEpochState.Action action) { + RemoteLogSegmentId remoteLogSegmentId = existingMetadata.remoteLogSegmentId(); + Map<Integer, Long> leaderEpochToOffset = existingMetadata.segmentLeaderEpochs(); + + // Go through all the leader epochs and apply the given action. + for (Map.Entry<Integer, Long> entry : leaderEpochToOffset.entrySet()) { + Integer leaderEpoch = entry.getKey(); + Long startOffset = entry.getValue(); + RemoteLogLeaderEpochState remoteLogLeaderEpochState = leaderEpochEntries.get(leaderEpoch); + + if (remoteLogLeaderEpochState == null) { + throw new IllegalStateException("RemoteLogLeaderEpochState does not exist for the leader epoch: " + + leaderEpoch); + } else { + long leaderEpochEndOffset = highestOffsetForEpoch(leaderEpoch, existingMetadata); + action.accept(remoteLogLeaderEpochState, startOffset, remoteLogSegmentId, leaderEpochEndOffset); + } + } + } + + private long highestOffsetForEpoch(Integer leaderEpoch, RemoteLogSegmentMetadata segmentMetadata) { + // Compute the highest offset for the leader epoch with in the segment + NavigableMap<Integer, Long> epochToOffset = segmentMetadata.segmentLeaderEpochs(); + Map.Entry<Integer, Long> nextEntry = epochToOffset.higherEntry(leaderEpoch); + + return nextEntry != null ? nextEntry.getValue() - 1 : segmentMetadata.endOffset(); + } + + /** + * Returns all the segments stored in this cache. + * + * @return + */ + public Iterator<RemoteLogSegmentMetadata> listAllRemoteLogSegments() { + // Return all the segments including unreferenced metadata. + return Collections.unmodifiableCollection(idToSegmentMetadata.values()).iterator(); + } + + /** + * Returns all the segments mapped to the leader epoch that exist in this cache sorted by {@link RemoteLogSegmentMetadata#startOffset()}. + * + * @param leaderEpoch leader epoch. + */ + public Iterator<RemoteLogSegmentMetadata> listRemoteLogSegments(int leaderEpoch) { + RemoteLogLeaderEpochState remoteLogLeaderEpochState = leaderEpochEntries.get(leaderEpoch); + if (remoteLogLeaderEpochState == null) { + return Collections.emptyIterator(); + } + + return remoteLogLeaderEpochState.listAllRemoteLogSegments(idToSegmentMetadata); + } + + /** + * Returns the highest offset of a segment for the given leader epoch if exists, else it returns empty. The segments + * that have reached the {@link RemoteLogSegmentState#COPY_SEGMENT_FINISHED} or later states are considered here. + * + * @param leaderEpoch leader epoch + */ + public Optional<Long> highestOffsetForEpoch(int leaderEpoch) { + RemoteLogLeaderEpochState entry = leaderEpochEntries.get(leaderEpoch); + return entry != null ? Optional.ofNullable(entry.highestLogOffset()) : Optional.empty(); + } + + /** + * This method tracks the given remote segment as not yet available for reads. It does not add the segment + * leader epoch offset mapping until this segment reaches COPY_SEGMENT_FINISHED state. + * + * @param remoteLogSegmentMetadata RemoteLogSegmentMetadata instance + */ + public void addCopyInProgressSegment(RemoteLogSegmentMetadata remoteLogSegmentMetadata) { Review comment: Is this method expected to be idempotent? ########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogLeaderEpochState.java ########## @@ -0,0 +1,172 @@ +/* + * 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.server.log.remote.metadata.storage; + +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentId; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadata; + +import java.util.ArrayList; +import java.util.Collections; +import java.util.Comparator; +import java.util.Iterator; +import java.util.Map; +import java.util.NavigableMap; +import java.util.Set; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentSkipListMap; + +/** + * This class represents the in-memory state of segments associated with a leader epoch. This includes the mapping of offset to + * segment ids and unreferenced segments which are not mapped to any offset but they exist in remote storage. + * <p> + * This is used by {@link RemoteLogMetadataCache} to track the segments for each leader epoch. + */ +class RemoteLogLeaderEpochState { + + // It contains offset to segment ids mapping with the segment state as COPY_SEGMENT_FINISHED. + private final NavigableMap<Long, RemoteLogSegmentId> offsetToId = new ConcurrentSkipListMap<>(); + + /** + * It represents unreferenced segments for this leader epoch. It contains the segments still in COPY_SEGMENT_STARTED + * and DELETE_SEGMENT_STARTED state or these have been replaced by callers with other segments having the same + * start offset for the leader epoch. These will be returned by {@link RemoteLogMetadataCache#listAllRemoteLogSegments()} + * and {@link RemoteLogMetadataCache#listRemoteLogSegments(int leaderEpoch)} so that callers can clean them up if + * they still exist. These will be cleaned from the cache once they reach DELETE_SEGMENT_FINISHED state. + */ + private final Set<RemoteLogSegmentId> unreferencedSegmentIds = ConcurrentHashMap.newKeySet(); + + // It represents the highest log offset of the segments that were updated with updateHighestLogOffset. + private volatile Long highestLogOffset; + + /** + * Returns all the segments associated with this leader epoch sorted by start offset in ascending order. + * + * @param idToSegmentMetadata mapping of id to segment metadata. This will be used to get RemoteLogSegmentMetadata + * for an id to be used for sorting. + */ + Iterator<RemoteLogSegmentMetadata> listAllRemoteLogSegments(Map<RemoteLogSegmentId, RemoteLogSegmentMetadata> idToSegmentMetadata) { + // Return all the segments including unreferenced metadata. + int size = offsetToId.size() + unreferencedSegmentIds.size(); + if (size == 0) { + return Collections.emptyIterator(); + } + + ArrayList<RemoteLogSegmentMetadata> metadataList = new ArrayList<>(size); + for (RemoteLogSegmentId id : offsetToId.values()) { + metadataList.add(idToSegmentMetadata.get(id)); + } + + if (!unreferencedSegmentIds.isEmpty()) { + for (RemoteLogSegmentId id : unreferencedSegmentIds) { + metadataList.add(idToSegmentMetadata.get(id)); + } + + // sort only when unreferenced entries exist as they are already sorted in offsetToId. + metadataList.sort(Comparator.comparingLong(RemoteLogSegmentMetadata::startOffset)); + } + + return metadataList.iterator(); + } + + void handleSegmentWithCopySegmentStartedState(RemoteLogSegmentId remoteLogSegmentId) { + // Add this to unreferenced set of segments for the respective leader epoch. + unreferencedSegmentIds.add(remoteLogSegmentId); Review comment: The add call won't replace an existing element with the same `remoteLogSegmentId`. Is that expected? For example, what happens if `addCopyInProgressSegment` is called twice but this line doesn't replace the existing entry? ########## File path: storage/src/main/java/org/apache/kafka/server/log/remote/metadata/storage/RemoteLogMetadataCache.java ########## @@ -0,0 +1,309 @@ +/* + * 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.server.log.remote.metadata.storage; + +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentId; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadata; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentMetadataUpdate; +import org.apache.kafka.server.log.remote.storage.RemoteLogSegmentState; +import org.apache.kafka.server.log.remote.storage.RemoteResourceNotFoundException; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +import java.util.Collections; +import java.util.Iterator; +import java.util.Map; +import java.util.NavigableMap; +import java.util.Objects; +import java.util.Optional; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentMap; + +/** + * This class provides an in-memory cache of remote log segment metadata. This maintains the lineage of segments + * with respect to leader epochs. + * <p> + * Remote log segment can go through the state transitions as mentioned in {@link RemoteLogSegmentState}. + * <p> + * This class will have all the segments which did not reach terminal state viz DELETE_SEGMENT_FINISHED. That means,any + * segment reaching the terminal state will get cleared from this instance. + * This class provides different methods to fetch segment metadata like {@link #remoteLogSegmentMetadata(int, long)}, + * {@link #highestOffsetForEpoch(int)}, {@link #listRemoteLogSegments(int)}, {@link #listAllRemoteLogSegments()}. Those + * methods have different semantics to fetch the segment based on its state. + * <p> + * <ul> + * <li> + * {@link RemoteLogSegmentState#COPY_SEGMENT_STARTED}: + * <br> + * Segment in this state indicates it is not yet copied successfully. So, these segments will not be + * accessible for reads but these are considered for cleanups when a partition is deleted. + * </li> + * <li> + * {@link RemoteLogSegmentState#COPY_SEGMENT_FINISHED}: + * <br> + * Segment in this state indicates it is successfully copied and it is available for reads. So, these segments + * will be accessible for reads. But this should be available for any cleanup activity like deleting segments by the + * caller of this class. + * </li> + * <li> + * {@link RemoteLogSegmentState#DELETE_SEGMENT_STARTED}: + * Segment in this state indicates it is getting deleted. That means, it is not available for reads. But it should be + * available for any cleanup activity like deleting segments by the caller of this class. + * </li> + * <li> + * {@link RemoteLogSegmentState#DELETE_SEGMENT_FINISHED}: + * Segment in this state indicate it is already deleted. That means, it is not available for any activity including + * reads or cleanup activity. This cache will clear entries containing this state. + * </li> + * </ul> + * + * <p> + * The below table summarizes whether the segment with the respective state are available for the given methods. + * <pre> + * +---------------------------------+----------------------+------------------------+-------------------------+-------------------------+ + * | Method / SegmentState | COPY_SEGMENT_STARTED | COPY_SEGMENT_FINISHED | DELETE_SEGMENT_STARTED | DELETE_SEGMENT_STARTED | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | remoteLogSegmentMetadata | No | Yes | No | No | + * | (int leaderEpoch, long offset) | | | | | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | listRemoteLogSegments | Yes | Yes | Yes | No | + * | (int leaderEpoch) | | | | | + * |---------------------------------+----------------------+------------------------+-------------------------+-------------------------| + * | listAllRemoteLogSegments() | Yes | Yes | Yes | No | + * | | | | | | + * +---------------------------------+----------------------+------------------------+-------------------------+-------------------------+ + * </pre> + * </p> + * <p></p> + */ +public class RemoteLogMetadataCache { + + private static final Logger log = LoggerFactory.getLogger(RemoteLogMetadataCache.class); + + // It contains all the segment-id to metadata mappings which did not reach the terminal state viz DELETE_SEGMENT_FINISHED. + private final ConcurrentMap<RemoteLogSegmentId, RemoteLogSegmentMetadata> idToSegmentMetadata + = new ConcurrentHashMap<>(); + + // It contains leader epoch to the respective entry containing the state. + private final ConcurrentMap<Integer, RemoteLogLeaderEpochState> leaderEpochEntries = new ConcurrentHashMap<>(); + + /** + * Returns {@link RemoteLogSegmentMetadata} if it exists for the given leader-epoch containing the offset and with + * {@link RemoteLogSegmentState#COPY_SEGMENT_FINISHED} state, else returns {@link Optional#empty()}. + * + * @param leaderEpoch leader epoch for the given offset + * @param offset offset + * @return the requested remote log segment metadata if it exists. + */ + public Optional<RemoteLogSegmentMetadata> remoteLogSegmentMetadata(int leaderEpoch, long offset) { + RemoteLogLeaderEpochState remoteLogLeaderEpochState = leaderEpochEntries.get(leaderEpoch); + + if (remoteLogLeaderEpochState == null) { + return Optional.empty(); + } + + // Look for floor entry as the given offset may exist in this entry. + RemoteLogSegmentId remoteLogSegmentId = remoteLogLeaderEpochState.floorEntry(offset); + if (remoteLogSegmentId == null) { + // If the offset is lower than the minimum offset available in metadata then return empty. + return Optional.empty(); + } + + RemoteLogSegmentMetadata metadata = idToSegmentMetadata.get(remoteLogSegmentId); + // Check whether the given offset with leaderEpoch exists in this segment. + // Check for epoch's offset boundaries with in this segment. + // 1. Get the next epoch's start offset -1 if exists + // 2. If no next epoch exists, then segment end offset can be considered as epoch's relative end offset. + Map.Entry<Integer, Long> nextEntry = metadata.segmentLeaderEpochs().higherEntry(leaderEpoch); + long epochEndOffset = (nextEntry != null) ? nextEntry.getValue() - 1 : metadata.endOffset(); + + // Return empty when target offset > epoch's end offset. + return offset > epochEndOffset ? Optional.empty() : Optional.of(metadata); + } + + public void updateRemoteLogSegmentMetadata(RemoteLogSegmentMetadataUpdate metadataUpdate) + throws RemoteResourceNotFoundException { + log.debug("Updating remote log segment metadata: [{}]", metadataUpdate); + Objects.requireNonNull(metadataUpdate, "metadataUpdate can not be null"); + + RemoteLogSegmentState targetState = metadataUpdate.state(); + RemoteLogSegmentId remoteLogSegmentId = metadataUpdate.remoteLogSegmentId(); + RemoteLogSegmentMetadata existingMetadata = idToSegmentMetadata.get(remoteLogSegmentId); + if (existingMetadata == null) { + throw new RemoteResourceNotFoundException("No remote log segment metadata found for :" + + remoteLogSegmentId); + } + + // Check the state transition. + checkStateTransition(existingMetadata.state(), targetState); + + switch (targetState) { + case COPY_SEGMENT_STARTED: + // Callers should use addCopyInProgressSegment to add RemoteLogSegmentMetadata with state as + // RemoteLogSegmentState.COPY_SEGMENT_STARTED. + throw new IllegalArgumentException("metadataUpdate: " + metadataUpdate + " with state " + RemoteLogSegmentState.COPY_SEGMENT_STARTED + + " can not be updated"); + case COPY_SEGMENT_FINISHED: + handleSegmentWithCopySegmentFinishedState(metadataUpdate, existingMetadata); + break; + case DELETE_SEGMENT_STARTED: + handleSegmentWithDeleteSegmentStartedState(metadataUpdate, existingMetadata); + break; + case DELETE_SEGMENT_FINISHED: + handleSegmentWithDeleteSegmentFinishedState(metadataUpdate, existingMetadata); + break; + default: + throw new IllegalArgumentException("Metadata with the state" + targetState + " is not supported"); Review comment: nit: add one whitespace at the end after "...state" -- This is an automated message from the Apache Git Service. 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