somandal commented on code in PR #16857: URL: https://github.com/apache/pinot/pull/16857#discussion_r2412045564
########## pinot-controller/src/main/java/org/apache/pinot/controller/helix/core/minion/DistributedTaskLockManager.java: ########## @@ -0,0 +1,423 @@ +/** + * 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.pinot.controller.helix.core.minion; + +import com.google.common.annotations.VisibleForTesting; +import java.util.ArrayList; +import java.util.Comparator; +import java.util.List; +import java.util.UUID; +import java.util.regex.Matcher; +import java.util.regex.Pattern; +import javax.annotation.Nullable; +import org.apache.helix.AccessOption; +import org.apache.helix.store.zk.ZkHelixPropertyStore; +import org.apache.helix.zookeeper.datamodel.ZNRecord; +import org.apache.pinot.common.metadata.ZKMetadataProvider; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + + +/** + * Manages distributed locks for minion task generation using ZooKeeper ephemeral sequential nodes. + * Uses ephemeral nodes that automatically disappear when the controller session ends. + * This approach provides automatic cleanup and is suitable for long-running task generation. + * Locks are held until explicitly released or the controller session terminates. + * Locks are at the table level, to ensure that only one type of task can be generated per table at any given time. + * <p> + * ZK EPHEMERAL_SEQUENTIAL Locks (see <a href="https://zookeeper.apache.org/doc/current/recipes.html#sc_recipes_Locks";> + * ZooKeeper Lock Recipe.</a> for more details): + * <ul> + * <li>Every lock is created with a lock prefix. Lock prefix used: [controllerName]-lock-[UUID]. The UUID helps + * differentiate between requests originating from the same controller at the same time + * <li>When ZK creates the ZNode, it appends a sequence number at the end. E.g. + * [controllerName]-lock-[UUID]-00000001 + * <li>The sequence number is used to identify the lock winner in case more than one lock node is created at the + * same time. The smallest sequence number always wins + * <li>The locks are EPHEMERAL in nature, meaning that once the session with ZK is lost, the lock is automatically + * cleaned up. Scenarios when the ZK session can be lost: a) controller shutdown, b) controller crash, c) ZK session + * expiry (e.g. long GC pauses can cause this) + * <li>This implementation does not set up watches as described in the recipe as the task lock is released whenever + * we identify that the lock is already acquired. Do not expect lock ownership to automatically change for the + * time being. If such support is needed in the future, this can be enhanced to add a watch on the neighboring + * lock node + * </ul> + * <p> + * Example of how the locks will work: + * <p> + * Say we have two controllers, and one controller happens to run 2 threads at the same time, all of which need to take + * the distributed lock. Each thread will create a distributed lock node, and the "-Lock" ZNode getChildren will return: + * <ul> + * <li>controller2-lock-xyzwx-00000002 + * <li>controller1-lock-abcde-00000001 + * <li>controller1-lock-ab345-00000003 + * </ul> + * <p> + * In the above, the controller1 with UUID abcde will win the lock as it has the smallest sequence number. The other + * two threads will clean up their locks and return error that the distributed lock could not be acquired. Controller1 + * will proceed with performing its tasks, and when done will release the lock. + */ +public class DistributedTaskLockManager { + private static final Logger LOGGER = LoggerFactory.getLogger(DistributedTaskLockManager.class); + + // Lock paths are constructed using ZKMetadataProvider + private static final String LOCK_OWNER_KEY = "lockOwner"; + private static final String LOCK_UUID_KEY = "lockUuid"; + private static final String LOCK_TIMESTAMP_MILLIS_KEY = "lockTimestampMillis"; + + // Define a custom comparator to compare strings of format '<controllerName>-lock-<uuid>-<sequenceNumber>' and sort + // them by the sequence number at the end + private static final Comparator<String> TASK_LOCK_SEQUENCE_ID_COMPARATOR = (s1, s2) -> { + // Regex to find the trailing sequence of digits + Pattern p = Pattern.compile("\\d+$"); + + // Extract the number from the first string + Matcher m1 = p.matcher(s1); + long num1 = m1.find() ? Long.parseLong(m1.group()) : 0; + + // Extract the number from the second string + Matcher m2 = p.matcher(s2); + long num2 = m2.find() ? Long.parseLong(m2.group()) : 0; + + return Long.compare(num1, num2); + }; + + private final ZkHelixPropertyStore<ZNRecord> _propertyStore; + private final String _controllerInstanceId; + + public DistributedTaskLockManager(ZkHelixPropertyStore<ZNRecord> propertyStore, String controllerInstanceId) { + _propertyStore = propertyStore; + _controllerInstanceId = controllerInstanceId; + + // Ensure base paths exist + ensureBasePaths(); + } + + /** + * Attempts to acquire a distributed lock at the table level for task generation using session-based locking. + * The lock is held until explicitly released or the controller session ends. + * + * @param tableNameWithType the table name with type + * @return TaskLock object if successful, null if lock could not be acquired + */ + @Nullable + public TaskLock acquireLock(String tableNameWithType) { + String lockBasePath = getLockBasePath(tableNameWithType); + + LOGGER.info("Attempting to acquire task generation lock: {} by controller: {}", tableNameWithType, + _controllerInstanceId); + + try { + // Check if task generation is already in progress + if (isTaskGenerationInProgress(tableNameWithType, lockBasePath)) { + LOGGER.info("Task generation already in progress for: {} by this or another controller", tableNameWithType); + return null; + } + + // Try to acquire the lock using ephemeral sequential node + TaskLock lock = tryAcquireSessionBasedLock(lockBasePath, tableNameWithType); + if (lock != null) { + LOGGER.info("Successfully acquired task generation lock: {} by controller: {}", tableNameWithType, + _controllerInstanceId); + return lock; + } else { + LOGGER.warn("Could not acquire lock: {} - another controller holds it", tableNameWithType); + return null; + } + } catch (Exception e) { + LOGGER.error("Error while trying to acquire lock: {}", tableNameWithType, e); + return null; + } + } + + private String getLockBasePath(String tableNameForPath) { + return ZKMetadataProvider.constructPropertyStorePathForMinionTaskGenerationLock(tableNameForPath); + } + + private String getBasePath() { + return ZKMetadataProvider.getPropertyStorePathForMinionTaskMetadataPrefix(); + } + + /** + * Releases a lock assuming successful completion. + */ + public boolean releaseLock(TaskLock lock) { + return releaseLock(lock, true); + } + + /** + * Releases a previously acquired session-based lock and marks task generation as completed. + * + * @param lock the lock to release + * @param success whether task generation completed successfully + * @return true if successfully released, false otherwise + */ + public boolean releaseLock(TaskLock lock, boolean success) { + if (lock == null) { + return true; + } + + String lockKey = lock.getLockKey(); + + try { + // Remove the ephemeral lock node + if (lock.getLockNodePath() != null) { + try { + boolean status = _propertyStore.remove(lock.getLockNodePath(), AccessOption.EPHEMERAL); + LOGGER.info("Removed ephemeral lock node: {}, removal success: {}", lock.getLockNodePath(), status); + } catch (Exception e) { + // Lock node might have already been removed due to session timeout - this is OK + LOGGER.warn("Ephemeral lock node already removed or session expired: {}", lock.getLockNodePath(), e); + } + } + + LOGGER.info("Successfully released task generation lock: {} by controller: {} (success: {})", lockKey, + _controllerInstanceId, success); + return true; + } catch (Exception e) { + LOGGER.error("Error while releasing lock: {}", lockKey, e); + return false; + } + } + + /** + * Force release the lock without checking if any tasks are in progress + */ + public boolean forceReleaseLock(String tableNameWithType) { + LOGGER.info("Trying to force release the lock for table: {}", tableNameWithType); + String lockBasePath = getLockBasePath(tableNameWithType); + + boolean released = true; + if (_propertyStore.exists(lockBasePath, AccessOption.PERSISTENT)) { + List<String> lockNodes = _propertyStore.getChildNames(lockBasePath, AccessOption.PERSISTENT); + if (lockNodes != null && !lockNodes.isEmpty()) { + // There are active ephemeral lock nodes, check if any are still valid and delete them + for (String nodeName : lockNodes) { + String nodePath = lockBasePath + "/" + nodeName; + if (_propertyStore.exists(nodePath, AccessOption.EPHEMERAL)) { + LOGGER.info("Lock for table: {} found at path: {}, trying to remove", tableNameWithType, nodePath); + boolean result = _propertyStore.remove(nodePath, AccessOption.EPHEMERAL); + if (!result) { + LOGGER.warn("Could not force release lock: {}", nodePath); + released = false; + } + } + } + } else { + LOGGER.info("No locks to force release, no child lock ZNodes found for table: {} under base: {}", + tableNameWithType, lockBasePath); + } + } else { + LOGGER.info("No locks to force release, no base lock ZNode: {} found for table: {}", lockBasePath, + tableNameWithType); + } + return released; + } + + /** + * Checks if any task generation is currently in progress for the given table. + * + * @param tableNameWithType the table name with type + * @return true if task generation is in progress, false otherwise + */ + @VisibleForTesting + boolean isTaskGenerationInProgress(String tableNameWithType) { + String lockBasePath = getLockBasePath(tableNameWithType); + return isTaskGenerationInProgress(tableNameWithType, lockBasePath); + } + + /** + * Internal method to check if task generation is in progress for a lock key. + */ + private boolean isTaskGenerationInProgress(String tableNameWithType, String lockBasePath) { + try { + if (!_propertyStore.exists(lockBasePath, AccessOption.PERSISTENT)) { + return false; + } + + // Check if there are any active ephemeral lock nodes + List<String> lockNodes = _propertyStore.getChildNames(lockBasePath, AccessOption.PERSISTENT); + if (lockNodes != null && !lockNodes.isEmpty()) { + // There are active ephemeral lock nodes, check if any are still valid + for (String nodeName : lockNodes) { + String nodePath = lockBasePath + "/" + nodeName; + if (_propertyStore.exists(nodePath, AccessOption.EPHEMERAL)) { + // Ephemeral node exists, meaning session is still alive and task should be in progress + return true; + } + } + } + return false; + } catch (Exception e) { + LOGGER.error("Error checking task generation status for: {}", tableNameWithType, e); + return false; + } + } + + /** + * Attempts to acquire a lock using ephemeral sequential nodes. + * Uses the ZooKeeper recipe for distributed locking with automatic cleanup. + */ + @VisibleForTesting + TaskLock tryAcquireSessionBasedLock(String lockBasePath, String lockKey) { + try { + long currentTimeMs = System.currentTimeMillis(); + + // Ensure the base lock directory exists + if (!_propertyStore.exists(lockBasePath, AccessOption.PERSISTENT)) { + ZNRecord baseRecord = new ZNRecord(lockKey); + _propertyStore.create(lockBasePath, baseRecord, AccessOption.PERSISTENT); + } + + // Create ephemeral sequential node for this controller, add an UUID to ensure that the path is unique in case + // multiple controller threads run at the same time + UUID uuid = UUID.randomUUID(); + String lockNodePrefix = lockBasePath + "/" + _controllerInstanceId + "-" + uuid + "-lock-"; + ZNRecord lockRecord = new ZNRecord(_controllerInstanceId); + lockRecord.setSimpleField(LOCK_OWNER_KEY, _controllerInstanceId); + lockRecord.setSimpleField(LOCK_TIMESTAMP_MILLIS_KEY, String.valueOf(currentTimeMs)); + lockRecord.setSimpleField(LOCK_UUID_KEY, uuid.toString()); + + // ZK will assign the sequence when creating EPHEMERAL_SEQUENTIAL ZNodes + boolean created = _propertyStore.create(lockNodePrefix, lockRecord, AccessOption.EPHEMERAL_SEQUENTIAL); + + if (created) { + // Find our actual node path by listing children and finding the one we just created, the UUID makes the path + // unique, even if we have multiple requests from the same controller + List<String> children = _propertyStore.getChildNames(lockBasePath, AccessOption.PERSISTENT); + List<String> allLockNodePathsForController = new ArrayList<>(); + String lockNodePath = null; + if (children != null) { + // Find any node that starts with our controller ID and contains "-lock-" + for (String child : children) { + if (child.startsWith(_controllerInstanceId) && child.contains("-lock-")) { + if (child.startsWith(_controllerInstanceId + "-" + uuid)) { + // If the node also contains the UUID, it's the lock we created + lockNodePath = lockBasePath + "/" + child; + } + allLockNodePathsForController.add(lockBasePath + "/" + child); + } + } + } + + LOGGER.info("Found {} lockNodePaths for controller instance: {}, list: {}, first lockNodePath cached: {}", + allLockNodePathsForController.size(), _controllerInstanceId, allLockNodePathsForController, lockNodePath); + + if (lockNodePath != null && allLockNodePathsForController.size() == 1) { + // Check if we got the lowest sequence number (i.e., we're first in line) + List<String> allChildren = _propertyStore.getChildNames(lockBasePath, AccessOption.PERSISTENT); + if (allChildren != null && !allChildren.isEmpty()) { + allChildren.sort(TASK_LOCK_SEQUENCE_ID_COMPARATOR); // Sort by sequence number + String ourNode = lockNodePath.substring(lockNodePath.lastIndexOf('/') + 1); + if (ourNode.equals(allChildren.get(0))) { + // We have the lock! + LOGGER.info("Acquired lock with ephemeral node: {}", lockNodePath); + return new TaskLock(lockKey, _controllerInstanceId, currentTimeMs, lockNodePath); + } else { + // Someone else has the lock, clean up our node + boolean status = _propertyStore.remove(lockNodePath, AccessOption.EPHEMERAL); + LOGGER.info("Did not get lock, removing ephemeral node: {}, return status: {}", lockNodePath, status); + return null; + } + } else { + // No children found, something went wrong, clean up + boolean status = _propertyStore.remove(lockNodePath, AccessOption.EPHEMERAL); + LOGGER.warn("No children found under {}. Remove lockNodePath status: {} for node: {}. Something must have " + + "gone wrong", lockBasePath, status, lockNodePath); + return null; + } + } else { + // Could not find our node path, or found too many paths for the same controller, cleanup failed creation + LOGGER.warn("Either lockNodePath: {} wasn't found, or too many locks ({}) found for the same controller: {}," + + "list of locks: {}", lockNodePath, allLockNodePathsForController.size(), _controllerInstanceId, + allLockNodePathsForController); + + if (lockNodePath != null) { + boolean status = _propertyStore.remove(lockNodePath, AccessOption.EPHEMERAL); + LOGGER.warn("Remove lockNodePath status: {} for path: {}", status, lockNodePath); + } + return null; + } + } + return null; + } catch (Exception e) { + LOGGER.error("Error creating ephemeral lock under path: {}, lockKey: {}", lockBasePath, lockKey, e); + return null; + } + } + + private void ensureBasePaths() { + try { + // Ensure minion task metadata base path exists + String basePath = getBasePath(); + if (!_propertyStore.exists(basePath, AccessOption.PERSISTENT)) { + ZNRecord baseRecord = new ZNRecord("MINION_TASK_METADATA"); Review Comment: removed the base path creation, parent ZNodes are anyways created and I was able to test using quickstart that this ensureBasePaths is not needed -- This is an automated message from the Apache Git Service. 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