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/*
* 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.clients;
import org.apache.kafka.common.TopicPartition;
import org.apache.kafka.common.protocol.Errors;
import org.apache.kafka.common.requests.FetchMetadata;
import org.apache.kafka.common.requests.FetchRequest.PartitionData;
import org.apache.kafka.common.requests.FetchResponse;
import org.apache.kafka.common.utils.LogContext;
import org.apache.kafka.common.utils.Utils;
import org.apache.logging.log4j.Logger;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.LinkedHashMap;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import static org.apache.kafka.common.requests.FetchMetadata.INVALID_SESSION_ID;
/**
* FetchSessionHandler maintains the fetch session state for connecting to a broker.
*
* Using the protocol outlined by KIP-227, clients can create incremental fetch sessions.
* These sessions allow the client to fetch information about a set of partition over
* and over, without explicitly enumerating all the partitions in the request and the
* response.
*
* FetchSessionHandler tracks the partitions which are in the session. It also
* determines which partitions need to be included in each fetch request, and what
* the attached fetch session metadata should be for each request. The corresponding
* class on the receiving broker side is FetchManager.
*/
public class FetchSessionHandler {
private final Logger log;
private final int node;
/**
* The metadata for the next fetch request.
*/
private FetchMetadata nextMetadata = FetchMetadata.INITIAL;
public FetchSessionHandler(LogContext logContext, int node) {
this.log = logContext.logger(FetchSessionHandler.class);
this.node = node;
}
/**
* All of the partitions which exist in the fetch request session.
*/
private LinkedHashMap sessionPartitions =
new LinkedHashMap<>(0);
public static class FetchRequestData {
/**
* The partitions to send in the fetch request.
*/
private final Map toSend;
/**
* The partitions to send in the request's "forget" list.
*/
private final List toForget;
/**
* All of the partitions which exist in the fetch request session.
*/
private final Map sessionPartitions;
/**
* The metadata to use in this fetch request.
*/
private final FetchMetadata metadata;
FetchRequestData(Map toSend,
List toForget,
Map sessionPartitions,
FetchMetadata metadata) {
this.toSend = toSend;
this.toForget = toForget;
this.sessionPartitions = sessionPartitions;
this.metadata = metadata;
}
/**
* Get the set of partitions to send in this fetch request.
*/
public Map toSend() {
return toSend;
}
/**
* Get a list of partitions to forget in this fetch request.
*/
public List toForget() {
return toForget;
}
/**
* Get the full set of partitions involved in this fetch request.
*/
public Map sessionPartitions() {
return sessionPartitions;
}
public FetchMetadata metadata() {
return metadata;
}
@Override
public String toString() {
if (metadata.isFull()) {
StringBuilder bld = new StringBuilder("FullFetchRequest(");
String prefix = "";
for (TopicPartition partition : toSend.keySet()) {
bld.append(prefix);
bld.append(partition);
prefix = ", ";
}
bld.append(")");
return bld.toString();
} else {
StringBuilder bld = new StringBuilder("IncrementalFetchRequest(toSend=(");
String prefix = "";
for (TopicPartition partition : toSend.keySet()) {
bld.append(prefix);
bld.append(partition);
prefix = ", ";
}
bld.append("), toForget=(");
prefix = "";
for (TopicPartition partition : toForget) {
bld.append(prefix);
bld.append(partition);
prefix = ", ";
}
bld.append("), implied=(");
prefix = "";
for (TopicPartition partition : sessionPartitions.keySet()) {
if (!toSend.containsKey(partition)) {
bld.append(prefix);
bld.append(partition);
prefix = ", ";
}
}
bld.append("))");
return bld.toString();
}
}
}
public class Builder {
/**
* The next partitions which we want to fetch.
*
* It is important to maintain the insertion order of this list by using a LinkedHashMap rather
* than a regular Map.
*
* One reason is that when dealing with FULL fetch requests, if there is not enough response
* space to return data from all partitions, the server will only return data from partitions
* early in this list.
*
* Another reason is because we make use of the list ordering to optimize the preparation of
* incremental fetch requests (see below).
*/
private LinkedHashMap next = new LinkedHashMap<>();
/**
* Mark that we want data from this partition in the upcoming fetch.
*/
public void add(TopicPartition topicPartition, PartitionData data) {
next.put(topicPartition, data);
}
public FetchRequestData build() {
if (nextMetadata.isFull()) {
if (log.isDebugEnabled()) {
log.debug("Built full fetch {} for node {} with {}.",
nextMetadata, node, partitionsToLogString(next.keySet()));
}
sessionPartitions = next;
next = null;
Map toSend =
Collections.unmodifiableMap(new LinkedHashMap<>(sessionPartitions));
return new FetchRequestData(toSend, Collections.emptyList(), toSend, nextMetadata);
}
List added = new ArrayList<>();
List removed = new ArrayList<>();
List altered = new ArrayList<>();
for (Iterator> iter =
sessionPartitions.entrySet().iterator(); iter.hasNext(); ) {
Entry entry = iter.next();
TopicPartition topicPartition = entry.getKey();
PartitionData prevData = entry.getValue();
PartitionData nextData = next.get(topicPartition);
if (nextData != null) {
if (prevData.equals(nextData)) {
// Omit this partition from the FetchRequest, because it hasn't changed
// since the previous request.
next.remove(topicPartition);
} else {
// Move the altered partition to the end of 'next'
next.remove(topicPartition);
next.put(topicPartition, nextData);
entry.setValue(nextData);
altered.add(topicPartition);
}
} else {
// Remove this partition from the session.
iter.remove();
// Indicate that we no longer want to listen to this partition.
removed.add(topicPartition);
}
}
// Add any new partitions to the session.
for (Entry entry : next.entrySet()) {
TopicPartition topicPartition = entry.getKey();
PartitionData nextData = entry.getValue();
if (sessionPartitions.containsKey(topicPartition)) {
// In the previous loop, all the partitions which existed in both sessionPartitions
// and next were moved to the end of next, or removed from next. Therefore,
// once we hit one of them, we know there are no more unseen entries to look
// at in next.
break;
}
sessionPartitions.put(topicPartition, nextData);
added.add(topicPartition);
}
if (log.isDebugEnabled()) {
log.debug("Built incremental fetch {} for node {}. Added {}, altered {}, removed {} " +
"out of {}", nextMetadata, node, partitionsToLogString(added),
partitionsToLogString(altered), partitionsToLogString(removed),
partitionsToLogString(sessionPartitions.keySet()));
}
Map toSend =
Collections.unmodifiableMap(new LinkedHashMap<>(next));
Map curSessionPartitions =
Collections.unmodifiableMap(new LinkedHashMap<>(sessionPartitions));
next = null;
return new FetchRequestData(toSend, Collections.unmodifiableList(removed),
curSessionPartitions, nextMetadata);
}
}
public Builder newBuilder() {
return new Builder();
}
private String partitionsToLogString(Collection partitions) {
if (!log.isTraceEnabled()) {
return String.format("%d partition(s)", partitions.size());
}
return "(" + Utils.join(partitions, ", ") + ")";
}
/**
* Return some partitions which are expected to be in a particular set, but which are not.
*
* @param toFind The partitions to look for.
* @param toSearch The set of partitions to search.
* @return null if all partitions were found; some of the missing ones
* in string form, if not.
*/
static Set findMissing(Set toFind, Set toSearch) {
Set ret = new LinkedHashSet<>();
for (TopicPartition partition : toFind) {
if (!toSearch.contains(partition)) {
ret.add(partition);
}
}
return ret;
}
/**
* Verify that a full fetch response contains all the partitions in the fetch session.
*
* @param response The response.
* @return True if the full fetch response partitions are valid.
*/
private String verifyFullFetchResponsePartitions(FetchResponse response) {
StringBuilder bld = new StringBuilder();
Set omitted =
findMissing(response.responseData().keySet(), sessionPartitions.keySet());
Set extra =
findMissing(sessionPartitions.keySet(), response.responseData().keySet());
if (!omitted.isEmpty()) {
bld.append("omitted=(").append(Utils.join(omitted, ", ")).append(", ");
}
if (!extra.isEmpty()) {
bld.append("extra=(").append(Utils.join(extra, ", ")).append(", ");
}
if ((!omitted.isEmpty()) || (!extra.isEmpty())) {
bld.append("response=(").append(Utils.join(response.responseData().keySet(), ", "));
return bld.toString();
}
return null;
}
/**
* Verify that the partitions in an incremental fetch response are contained in the session.
*
* @param response The response.
* @return True if the incremental fetch response partitions are valid.
*/
private String verifyIncrementalFetchResponsePartitions(FetchResponse response) {
Set extra =
findMissing(response.responseData().keySet(), sessionPartitions.keySet());
if (!extra.isEmpty()) {
StringBuilder bld = new StringBuilder();
bld.append("extra=(").append(Utils.join(extra, ", ")).append("), ");
bld.append("response=(").append(
Utils.join(response.responseData().keySet(), ", ")).append("), ");
return bld.toString();
}
return null;
}
/**
* Create a string describing the partitions in a FetchResponse.
*
* @param response The FetchResponse.
* @return The string to log.
*/
private String responseDataToLogString(FetchResponse response) {
if (!log.isTraceEnabled()) {
int implied = sessionPartitions.size() - response.responseData().size();
if (implied > 0) {
return String.format(" with %d response partition(s), %d implied partition(s)",
response.responseData().size(), implied);
} else {
return String.format(" with %d response partition(s)",
response.responseData().size());
}
}
StringBuilder bld = new StringBuilder();
bld.append(" with response=(").
append(Utils.join(response.responseData().keySet(), ", ")).
append(")");
String prefix = ", implied=(";
String suffix = "";
for (TopicPartition partition : sessionPartitions.keySet()) {
if (!response.responseData().containsKey(partition)) {
bld.append(prefix);
bld.append(partition);
prefix = ", ";
suffix = ")";
}
}
bld.append(suffix);
return bld.toString();
}
/**
* Handle the fetch response.
*
* @param response The response.
* @return True if the response is well-formed; false if it can't be processed
* because of missing or unexpected partitions.
*/
public boolean handleResponse(FetchResponse response) {
if (response.error() != Errors.NONE) {
log.info("Node {} was unable to process the fetch request with {}: {}.",
node, nextMetadata, response.error());
if (response.error() == Errors.FETCH_SESSION_ID_NOT_FOUND) {
nextMetadata = FetchMetadata.INITIAL;
} else {
nextMetadata = nextMetadata.nextCloseExisting();
}
return false;
} else if (nextMetadata.isFull()) {
String problem = verifyFullFetchResponsePartitions(response);
if (problem != null) {
log.info("Node {} sent an invalid full fetch response with {}", node, problem);
nextMetadata = FetchMetadata.INITIAL;
return false;
} else if (response.sessionId() == INVALID_SESSION_ID) {
if (log.isDebugEnabled())
log.debug("Node {} sent a full fetch response{}", node, responseDataToLogString(response));
nextMetadata = FetchMetadata.INITIAL;
return true;
} else {
// The server created a new incremental fetch session.
if (log.isDebugEnabled())
log.debug("Node {} sent a full fetch response that created a new incremental " +
"fetch session {}{}", node, response.sessionId(), responseDataToLogString(response));
nextMetadata = FetchMetadata.newIncremental(response.sessionId());
return true;
}
} else {
String problem = verifyIncrementalFetchResponsePartitions(response);
if (problem != null) {
log.info("Node {} sent an invalid incremental fetch response with {}", node, problem);
nextMetadata = nextMetadata.nextCloseExisting();
return false;
} else if (response.sessionId() == INVALID_SESSION_ID) {
// The incremental fetch session was closed by the server.
if (log.isDebugEnabled())
log.debug("Node {} sent an incremental fetch response closing session {}{}",
node, nextMetadata.sessionId(), responseDataToLogString(response));
nextMetadata = FetchMetadata.INITIAL;
return true;
} else {
// The incremental fetch session was continued by the server.
if (log.isDebugEnabled())
log.debug("Node {} sent an incremental fetch response for session {}{}",
node, response.sessionId(), responseDataToLogString(response));
nextMetadata = nextMetadata.nextIncremental();
return true;
}
}
}
/**
* Handle an error sending the prepared request.
*
* When a network error occurs, we close any existing fetch session on our next request,
* and try to create a new session.
*
* @param t The exception.
*/
public void handleError(Throwable t) {
log.info("Error sending fetch request {} to node {}: {}.", nextMetadata, node, t);
nextMetadata = nextMetadata.nextCloseExisting();
}
}
