ivandika3 commented on code in PR #11418: URL: https://github.com/apache/ozone/pull/11418#discussion_r4202423972
########## hadoop-ozone/common/src/main/java/org/apache/hadoop/ozone/om/ha/FollowerReadFailoverProxyProviderBase.java: ########## @@ -0,0 +1,167 @@ +/* + * 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.hadoop.ozone.om.ha; + +import org.apache.hadoop.ozone.OmUtils; +import org.apache.hadoop.ozone.om.helpers.ReadConsistency; +import org.apache.hadoop.ozone.om.protocolPB.OzoneManagerProtocolPB; +import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.OMRequest; +import org.apache.hadoop.ozone.protocol.proto.OzoneManagerProtocolProtos.ReadConsistencyHint; +import org.apache.ratis.util.Preconditions; +import org.slf4j.Logger; +import org.slf4j.LoggerFactory; + +/** + * Base class for the OM follower read failover proxy providers. + * <p> + * It keeps the follower read configuration and selects the OM node to send follower reads to. + * Leader-based failover is delegated to the underlying {@link OMFailoverProxyProviderBase}. + */ +public abstract class FollowerReadFailoverProxyProviderBase { + private static final Logger LOG = LoggerFactory.getLogger(FollowerReadFailoverProxyProviderBase.class); + + /** Whether follower reads are supported by the OM service. */ + private volatile boolean omServiceSupportsFollowerRead; + + /** Whether eligible reads without an explicit consistency hint use followers. */ + private final boolean defaultFollowerReadEnabled; + + /** The read consistency hint used when follower read is enabled. */ + private final ReadConsistencyHint followerReadConsistency; + /** The read consistency hint used when follower read is disabled or when follower read fails. */ + private final ReadConsistencyHint leaderReadConsistency; + + /** + * The index of the OM node used for follower read, in the order of the leader proxy's OM nodes. + * Should only be accessed in synchronized methods. + */ + private int currentIndex = 0; + + protected FollowerReadFailoverProxyProviderBase(ReadConsistency followerReadConsistencyType, + ReadConsistency leaderReadConsistencyType, boolean defaultFollowerReadEnabled) { + Preconditions.assertTrue(followerReadConsistencyType.allowFollowerRead(), + "Invalid follower read consistency " + followerReadConsistencyType); + Preconditions.assertTrue(!leaderReadConsistencyType.allowFollowerRead(), + "Invalid leader read consistency " + leaderReadConsistencyType); + // At the start, we don't know whether OM service supports follower read. Therefore, if the client + // is configured to use follower read, we should assume that OM service supports follower read and + // only sets this to false if there is an evidence otherwise (i.e. OM throws OMNotLeaderException). + this.omServiceSupportsFollowerRead = true; + this.defaultFollowerReadEnabled = defaultFollowerReadEnabled; + this.followerReadConsistency = followerReadConsistencyType.getHint(); + this.leaderReadConsistency = leaderReadConsistencyType.getHint(); + } + + /** @return the inner proxy provider used for leader-based failover. */ + protected abstract OMFailoverProxyProviderBase<OzoneManagerProtocolPB> getLeaderProxy(); + + public boolean isOmServiceSupportsFollowerRead() { + return omServiceSupportsFollowerRead; + } + + /** + * Stop sending reads to OM followers, since an OM follower does not support follower read + * (i.e. it throws OMNotLeaderException). + */ + protected void disableFollowerRead() { + omServiceSupportsFollowerRead = false; + } + + /** + * Determines whether an eligible read request may be sent to an OM follower. + * + * <p>An explicit consistency hint takes precedence over the configured + * default follower-read behavior.</p> + */ + protected boolean shouldUseFollowerRead(OMRequest request) { + if (!omServiceSupportsFollowerRead || !OmUtils.shouldSendToFollower(request)) { + return false; + } + if (request.hasReadConsistencyHint()) { + return getReadConsistency(request).allowFollowerRead(); + } + return defaultFollowerReadEnabled; + } + + /** + * Add the default follower or leader read consistency hint to the request + * if the request does not have a consistency hint. + */ + protected OMRequest addReadConsistencyHint(OMRequest request, boolean followerRead) { + if (request.hasReadConsistencyHint()) { + return request; + } + final ReadConsistencyHint hint = followerRead ? followerReadConsistency : leaderReadConsistency; + return request.toBuilder().setReadConsistencyHint(hint).build(); + } + + protected static ReadConsistency getReadConsistency(OMRequest request) { + return request.hasReadConsistencyHint() + ? ReadConsistency.fromProto(request.getReadConsistencyHint().getReadConsistency()) + : ReadConsistency.DEFAULT; + } + + protected int getOMNodeCount() { + return getLeaderProxy().getOMProxyMap().size(); + } + + protected synchronized String getCurrentFollowerReadNodeId() { + return getLeaderProxy().getOMProxyMap().getNodeId(currentIndex); + } + + /** + * Move to the next OM node for follower read. If the current node is no longer + * the given node, the call is ignored; this is to handle concurrent calls + * (to avoid changing the node multiple times). + * + * @param nodeId the expected current node. + */ + protected synchronized void changeFollowerReadNodeId(String nodeId) { + if (nodeId.equals(getCurrentFollowerReadNodeId())) { + currentIndex = (currentIndex + 1) % getOMNodeCount(); + LOG.debug("Changed follower read OM node from {} to {}", nodeId, getCurrentFollowerReadNodeId()); + } + } + + /** + * Select the OM node to send a follower read with the given consistency to. + * A {@link ReadConsistency#LOCAL_LEASE} read skips the leader known by the leader proxy. + * + * @return the selected node, or null if no node other than the known leader is available. + */ + protected synchronized String selectFollowerReadNodeId(ReadConsistency readConsistency) { + String nodeId = getCurrentFollowerReadNodeId(); + if (readConsistency != ReadConsistency.LOCAL_LEASE) { + return nodeId; + } + + final String leaderNodeId = getLeaderProxy().getCurrentProxyOMNodeId(); + for (int i = 0; i < getOMNodeCount(); i++) { + if (!nodeId.equals(leaderNodeId)) { + return nodeId; + } + changeFollowerReadNodeId(nodeId); + nodeId = getCurrentFollowerReadNodeId(); + } + return null; + } Review Comment: In the previous logic, we don't necessarily need to send to a follower (for perf reason since currently things linearizable read latency is significantly higher than leader read), but in this logic we always prioritize follower first? I suggest we address behavior change in another ticket (and probably gate it in a configuration with name similar to follower affinity in `OmMetadataGenerator`). -- 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. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
