leventov commented on a change in pull request #9172: Fix huge number of watches in zk URL: https://github.com/apache/druid/pull/9172#discussion_r365805635
########## File path: server/src/main/java/org/apache/druid/curator/announcement/NodeAnnouncer.java ########## @@ -0,0 +1,350 @@ +/* + * 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.druid.curator.announcement; + +import com.google.common.annotations.VisibleForTesting; +import org.apache.curator.framework.CuratorFramework; +import org.apache.curator.framework.api.transaction.CuratorOp; +import org.apache.curator.framework.recipes.cache.ChildData; +import org.apache.curator.framework.recipes.cache.NodeCache; +import org.apache.druid.java.util.common.IAE; +import org.apache.druid.java.util.common.ISE; +import org.apache.druid.java.util.common.guava.CloseQuietly; +import org.apache.druid.java.util.common.io.Closer; +import org.apache.druid.java.util.common.lifecycle.LifecycleStart; +import org.apache.druid.java.util.common.lifecycle.LifecycleStop; +import org.apache.druid.java.util.common.logger.Logger; +import org.apache.druid.server.ZKPathsUtils; +import org.apache.zookeeper.CreateMode; +import org.apache.zookeeper.KeeperException; + +import javax.annotation.concurrent.GuardedBy; +import java.util.ArrayList; +import java.util.Arrays; +import java.util.List; +import java.util.Set; +import java.util.concurrent.ConcurrentHashMap; +import java.util.concurrent.ConcurrentMap; +import java.util.concurrent.CopyOnWriteArrayList; + +/** + * NodeAnnouncer announces single node on Zookeeper and only watches this node, + * while {@link Announcer} watches all child paths, not only this node + */ +public class NodeAnnouncer +{ + private static final Logger log = new Logger(NodeAnnouncer.class); + + private final CuratorFramework curator; + + /** + * In case a path is added to this collection in {@link #announce} before zk is connected, + * should remember the path and do announce in {@link #start} later. + */ + private final List<Announceable> toAnnounce = new ArrayList<>(); + /** + * In case a path is added to this collection in {@link #update} before zk is connected, + * should remember the path and do update in {@link #start} later. + */ + @GuardedBy("toAnnounce") + private final List<Announceable> toUpdate = new ArrayList<>(); + private final ConcurrentMap<String, NodeCache> listeners = new ConcurrentHashMap<>(); + private final ConcurrentMap<String, byte[]> announcedPaths = new ConcurrentHashMap<>(); + /** + * Only the one created the parent path can drop the parent path, so should remember these created parents. + */ + private final List<String> pathsCreatedInThisAnnouncer = new CopyOnWriteArrayList<>(); + + private boolean started = false; + + public NodeAnnouncer(CuratorFramework curator) + { + this.curator = curator; + } + + @VisibleForTesting + Set<String> getAddedPaths() + { + return announcedPaths.keySet(); + } + + @LifecycleStart + @SuppressWarnings("DuplicatedCode") + public void start() + { + log.info("Starting announcer"); + synchronized (toAnnounce) { + if (started) { + return; + } + + started = true; + + for (Announceable announceable : toAnnounce) { + announce(announceable.path, announceable.bytes, announceable.removeParentsIfCreated); + } + toAnnounce.clear(); + + for (Announceable announceable : toUpdate) { + update(announceable.path, announceable.bytes); + } + toUpdate.clear(); + } + } + + @LifecycleStop + public void stop() + { + log.info("Stopping announcer"); + synchronized (toAnnounce) { + if (!started) { + return; + } + + started = false; + + Closer closer = Closer.create(); + for (NodeCache cache : listeners.values()) { + closer.register(cache); + } + CloseQuietly.close(closer); + + for (String announcementPath : announcedPaths.keySet()) { + unannounce(announcementPath); + } + + if (!pathsCreatedInThisAnnouncer.isEmpty()) { + final List<CuratorOp> deleteOps = new ArrayList<>(pathsCreatedInThisAnnouncer.size()); + for (String parent : pathsCreatedInThisAnnouncer) { + try { + deleteOps.add(curator.transactionOp().delete().forPath(parent)); + } + catch (Exception e) { + log.error(e, "Unable to delete parent[%s].", parent); + } + } + try { + curator.transaction().forOperations(deleteOps); + } + catch (Exception e) { + log.error(e, "Unable to commit transaction."); + } + } + } + } + + /** + * Like announce(path, bytes, true). + */ + public void announce(String path, byte[] bytes) + { + announce(path, bytes, true); + } + + /** + * Announces the provided bytes at the given path. Announcement means that it will create an ephemeral node + * and monitor it to make sure that it always exists until it is unannounced or this object is closed. + * + * @param path The path to announce at + * @param bytes The payload to announce + * @param removeParentIfCreated remove parent of "path" if we had created that parent + */ + public void announce(String path, byte[] bytes, boolean removeParentIfCreated) + { + synchronized (toAnnounce) { + if (!started) { + toAnnounce.add(new Announceable(path, bytes, removeParentIfCreated)); + return; + } + } + + final String parentPath = ZKPathsUtils.getParentPath(path); + boolean buildParentPath = false; + + byte[] value = announcedPaths.get(path); + + if (value == null) { + try { + if (curator.checkExists().forPath(parentPath) == null) { + buildParentPath = true; + } + } + catch (Exception e) { + log.debug(e, "Problem checking if the parent existed, ignoring."); + } + + // Synchronize to make sure that I only create a listener once. + synchronized (toAnnounce) { + if (!listeners.containsKey(path)) { + final NodeCache cache = new NodeCache(curator, path, true); + cache.getListenable().addListener( + () -> { + ChildData currentData = cache.getCurrentData(); + if (currentData == null) { + final byte[] value1 = announcedPaths.get(path); + if (value1 != null) { + log.info("Node[%s] dropped, reinstating.", path); + createAnnouncement(path, value1); + } + } + } + ); + + if (started) { + if (buildParentPath) { + createPath(parentPath, removeParentIfCreated); + } + startCache(cache); + listeners.put(path, cache); + } + } + } + } + + boolean created = false; + synchronized (toAnnounce) { + if (started) { + byte[] oldBytes = announcedPaths.putIfAbsent(path, bytes); + + if (oldBytes == null) { + created = true; + } else if (!Arrays.equals(oldBytes, bytes)) { + throw new IAE("Cannot reannounce different values under the same path"); + } + } + } + + if (created) { + try { + createAnnouncement(path, bytes); + } + catch (Exception e) { + throw new RuntimeException(e); + } + } + } + + public void update(final String path, final byte[] bytes) + { + synchronized (toAnnounce) { + if (!started) { + // removeParentsIfCreated is not relevant for updates; use dummy value "false". + toUpdate.add(new Announceable(path, bytes, false)); + return; + } + } + + byte[] oldBytes = announcedPaths.get(path); + + if (oldBytes == null) { + throw new ISE("Cannot update a path[%s] that hasn't been announced!", path); + } + + synchronized (toAnnounce) { + try { + if (!Arrays.equals(oldBytes, bytes)) { + announcedPaths.put(path, bytes); + updateAnnouncement(path, bytes); + } + } + catch (Exception e) { + throw new RuntimeException(e); + } + } + } + + private void createAnnouncement(final String path, byte[] value) throws Exception + { + curator.create().compressed().withMode(CreateMode.EPHEMERAL).inBackground().forPath(path, value); + } + + private void updateAnnouncement(final String path, final byte[] value) throws Exception + { + curator.setData().compressed().inBackground().forPath(path, value); + } + + /** + * Unannounces an announcement created at path. Note that if all announcements get removed, the Announcer + * will continue to have ZK watches on paths because clearing them out is a source of ugly race conditions. + * <p/> + * If you need to completely clear all the state of what is being watched and announced, stop() the Announcer. + * + * @param path the path to unannounce + */ + public void unannounce(String path) + { + log.info("unannouncing [%s]", path); + final byte[] value = announcedPaths.remove(path); + + if (value == null) { + log.error("Path[%s] not announced, cannot unannounce.", path); + return; + } + + try { + curator.transaction().forOperations(curator.transactionOp().delete().forPath(path)); + } + catch (KeeperException.NoNodeException e) { + log.info("node[%s] didn't exist anyway...", path); + } + catch (Exception e) { + throw new RuntimeException(e); + } + } + + private void startCache(NodeCache cache) + { + try { + cache.start(); + } + catch (Exception e) { + CloseQuietly.close(cache); + throw new RuntimeException(e); + } + } + + private void createPath(String parentPath, boolean removeParentsIfCreated) + { + try { + curator.create().creatingParentsIfNeeded().forPath(parentPath); + if (removeParentsIfCreated) { + pathsCreatedInThisAnnouncer.add(parentPath); + } + log.debug("Created parentPath[%s], %s remove on stop() called.", parentPath, removeParentsIfCreated ? "will" : "will not"); + } + catch (Exception e) { + log.error(e, "Problem creating parentPath[%s], someone else created it first?", parentPath); Review comment: This doesn't look super reasonable to me just to swallow the error here. I think it can break the logic of `announce()` (even if it cannot, it's quite hard to see, why exactly, therefore at least some explanations should be added) or lead to some kind of grey failure. @himanshug @nishantmonu51 WDYT? ---------------------------------------------------------------- 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. For queries about this service, please contact Infrastructure at: [email protected] With regards, Apache Git Services --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
