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/*
* SPDX-License-Identifier: Apache-2.0
*
* The OpenSearch Contributors require contributions made to
* this file be licensed under the Apache-2.0 license or a
* compatible open source license.
*/
/*
* Licensed to Elasticsearch under one or more contributor
* license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright
* ownership. Elasticsearch 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.
*/
/*
* Modifications Copyright OpenSearch Contributors. See
* GitHub history for details.
*/
package org.opensearch.gateway;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.message.ParameterizedMessage;
import org.opensearch.ExceptionsHelper;
import org.opensearch.OpenSearchTimeoutException;
import org.opensearch.action.FailedNodeException;
import org.opensearch.action.support.nodes.BaseNodeResponse;
import org.opensearch.action.support.nodes.BaseNodesResponse;
import org.opensearch.cluster.node.DiscoveryNode;
import org.opensearch.cluster.node.DiscoveryNodes;
import org.opensearch.cluster.routing.allocation.RoutingAllocation;
import org.opensearch.common.Nullable;
import org.opensearch.common.lease.Releasable;
import org.opensearch.core.action.ActionListener;
import org.opensearch.core.concurrency.OpenSearchRejectedExecutionException;
import org.opensearch.core.index.shard.ShardId;
import org.opensearch.transport.ReceiveTimeoutTransportException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.concurrent.atomic.AtomicLong;
import static java.util.Collections.emptySet;
import static java.util.Collections.unmodifiableSet;
/**
* Allows to asynchronously fetch shard related data from other nodes for allocation, without blocking
* the cluster update thread.
*
* The async fetch logic maintains a map of which nodes are being fetched from in an async manner,
* and once the results are back, it makes sure to schedule a reroute to make sure those results will
* be taken into account.
*
* @opensearch.internal
*/
public abstract class AsyncShardFetch implements Releasable {
/**
* An action that lists the relevant shard data that needs to be fetched.
*/
public interface Lister, NodeResponse extends BaseNodeResponse> {
void list(ShardId shardId, @Nullable String customDataPath, DiscoveryNode[] nodes, ActionListener listener);
}
protected final Logger logger;
protected final String type;
protected final ShardId shardId;
protected final String customDataPath;
private final Lister, T> action;
private final Map> cache = new HashMap<>();
private final Set nodesToIgnore = new HashSet<>();
private final AtomicLong round = new AtomicLong();
private boolean closed;
@SuppressWarnings("unchecked")
protected AsyncShardFetch(
Logger logger,
String type,
ShardId shardId,
String customDataPath,
Lister, T> action
) {
this.logger = logger;
this.type = type;
this.shardId = Objects.requireNonNull(shardId);
this.customDataPath = Objects.requireNonNull(customDataPath);
this.action = (Lister, T>) action;
}
@Override
public synchronized void close() {
this.closed = true;
}
/**
* Returns the number of async fetches that are currently ongoing.
*/
public synchronized int getNumberOfInFlightFetches() {
int count = 0;
for (NodeEntry nodeEntry : cache.values()) {
if (nodeEntry.isFetching()) {
count++;
}
}
return count;
}
/**
* Fetches the data for the relevant shard. If there any ongoing async fetches going on, or new ones have
* been initiated by this call, the result will have no data.
*
* The ignoreNodes are nodes that are supposed to be ignored for this round, since fetching is async, we need
* to keep them around and make sure we add them back when all the responses are fetched and returned.
*/
public synchronized FetchResult fetchData(DiscoveryNodes nodes, Set ignoreNodes) {
if (closed) {
throw new IllegalStateException(shardId + ": can't fetch data on closed async fetch");
}
nodesToIgnore.addAll(ignoreNodes);
fillShardCacheWithDataNodes(cache, nodes);
List> nodesToFetch = findNodesToFetch(cache);
if (nodesToFetch.isEmpty() == false) {
// mark all node as fetching and go ahead and async fetch them
// use a unique round id to detect stale responses in processAsyncFetch
final long fetchingRound = round.incrementAndGet();
for (NodeEntry nodeEntry : nodesToFetch) {
nodeEntry.markAsFetching(fetchingRound);
}
DiscoveryNode[] discoNodesToFetch = nodesToFetch.stream()
.map(NodeEntry::getNodeId)
.map(nodes::get)
.toArray(DiscoveryNode[]::new);
asyncFetch(discoNodesToFetch, fetchingRound);
}
// if we are still fetching, return null to indicate it
if (hasAnyNodeFetching(cache)) {
return new FetchResult<>(shardId, null, emptySet());
} else {
// nothing to fetch, yay, build the return value
Map fetchData = new HashMap<>();
Set failedNodes = new HashSet<>();
for (Iterator>> it = cache.entrySet().iterator(); it.hasNext();) {
Map.Entry> entry = it.next();
String nodeId = entry.getKey();
NodeEntry nodeEntry = entry.getValue();
DiscoveryNode node = nodes.get(nodeId);
if (node != null) {
if (nodeEntry.isFailed()) {
// if its failed, remove it from the list of nodes, so if this run doesn't work
// we try again next round to fetch it again
it.remove();
failedNodes.add(nodeEntry.getNodeId());
} else {
if (nodeEntry.getValue() != null) {
fetchData.put(node, nodeEntry.getValue());
}
}
}
}
Set allIgnoreNodes = unmodifiableSet(new HashSet<>(nodesToIgnore));
// clear the nodes to ignore, we had a successful run in fetching everything we can
// we need to try them if another full run is needed
nodesToIgnore.clear();
// if at least one node failed, make sure to have a protective reroute
// here, just case this round won't find anything, and we need to retry fetching data
if (failedNodes.isEmpty() == false || allIgnoreNodes.isEmpty() == false) {
reroute(shardId, "nodes failed [" + failedNodes.size() + "], ignored [" + allIgnoreNodes.size() + "]");
}
return new FetchResult<>(shardId, fetchData, allIgnoreNodes);
}
}
/**
* Called by the response handler of the async action to fetch data. Verifies that its still working
* on the same cache generation, otherwise the results are discarded. It then goes and fills the relevant data for
* the shard (response + failures), issuing a reroute at the end of it to make sure there will be another round
* of allocations taking this new data into account.
*/
protected synchronized void processAsyncFetch(List responses, List failures, long fetchingRound) {
if (closed) {
// we are closed, no need to process this async fetch at all
logger.trace("{} ignoring fetched [{}] results, already closed", shardId, type);
return;
}
logger.trace("{} processing fetched [{}] results", shardId, type);
if (responses != null) {
for (T response : responses) {
NodeEntry nodeEntry = cache.get(response.getNode().getId());
if (nodeEntry != null) {
if (nodeEntry.getFetchingRound() != fetchingRound) {
assert nodeEntry.getFetchingRound() > fetchingRound : "node entries only replaced by newer rounds";
logger.trace(
"{} received response for [{}] from node {} for an older fetching round (expected: {} but was: {})",
shardId,
nodeEntry.getNodeId(),
type,
nodeEntry.getFetchingRound(),
fetchingRound
);
} else if (nodeEntry.isFailed()) {
logger.trace(
"{} node {} has failed for [{}] (failure [{}])",
shardId,
nodeEntry.getNodeId(),
type,
nodeEntry.getFailure()
);
} else {
// if the entry is there, for the right fetching round and not marked as failed already, process it
logger.trace("{} marking {} as done for [{}], result is [{}]", shardId, nodeEntry.getNodeId(), type, response);
nodeEntry.doneFetching(response);
}
}
}
}
if (failures != null) {
for (FailedNodeException failure : failures) {
logger.trace("{} processing failure {} for [{}]", shardId, failure, type);
NodeEntry nodeEntry = cache.get(failure.nodeId());
if (nodeEntry != null) {
if (nodeEntry.getFetchingRound() != fetchingRound) {
assert nodeEntry.getFetchingRound() > fetchingRound : "node entries only replaced by newer rounds";
logger.trace(
"{} received failure for [{}] from node {} for an older fetching round (expected: {} but was: {})",
shardId,
nodeEntry.getNodeId(),
type,
nodeEntry.getFetchingRound(),
fetchingRound
);
} else if (nodeEntry.isFailed() == false) {
// if the entry is there, for the right fetching round and not marked as failed already, process it
Throwable unwrappedCause = ExceptionsHelper.unwrapCause(failure.getCause());
// if the request got rejected or timed out, we need to try it again next time...
if (unwrappedCause instanceof OpenSearchRejectedExecutionException
|| unwrappedCause instanceof ReceiveTimeoutTransportException
|| unwrappedCause instanceof OpenSearchTimeoutException) {
nodeEntry.restartFetching();
} else {
logger.warn(
() -> new ParameterizedMessage(
"{}: failed to list shard for {} on node [{}]",
shardId,
type,
failure.nodeId()
),
failure
);
nodeEntry.doneFetching(failure.getCause());
}
}
}
}
}
reroute(shardId, "post_response");
}
/**
* Implement this in order to scheduled another round that causes a call to fetch data.
*/
protected abstract void reroute(ShardId shardId, String reason);
/**
* Clear cache for node, ensuring next fetch will fetch a fresh copy.
*/
synchronized void clearCacheForNode(String nodeId) {
cache.remove(nodeId);
}
/**
* Fills the shard fetched data with new (data) nodes and a fresh NodeEntry, and removes from
* it nodes that are no longer part of the state.
*/
private void fillShardCacheWithDataNodes(Map> shardCache, DiscoveryNodes nodes) {
// verify that all current data nodes are there
for (final DiscoveryNode node : nodes.getDataNodes().values()) {
if (shardCache.containsKey(node.getId()) == false) {
shardCache.put(node.getId(), new NodeEntry(node.getId()));
}
}
// remove nodes that are not longer part of the data nodes set
shardCache.keySet().removeIf(nodeId -> !nodes.nodeExists(nodeId));
}
/**
* Finds all the nodes that need to be fetched. Those are nodes that have no
* data, and are not in fetch mode.
*/
private List> findNodesToFetch(Map> shardCache) {
List> nodesToFetch = new ArrayList<>();
for (NodeEntry nodeEntry : shardCache.values()) {
if (nodeEntry.hasData() == false && nodeEntry.isFetching() == false) {
nodesToFetch.add(nodeEntry);
}
}
return nodesToFetch;
}
/**
* Are there any nodes that are fetching data?
*/
private boolean hasAnyNodeFetching(Map> shardCache) {
for (NodeEntry nodeEntry : shardCache.values()) {
if (nodeEntry.isFetching()) {
return true;
}
}
return false;
}
/**
* Async fetches data for the provided shard with the set of nodes that need to be fetched from.
*/
// visible for testing
void asyncFetch(final DiscoveryNode[] nodes, long fetchingRound) {
logger.trace("{} fetching [{}] from {}", shardId, type, nodes);
action.list(shardId, customDataPath, nodes, new ActionListener>() {
@Override
public void onResponse(BaseNodesResponse response) {
processAsyncFetch(response.getNodes(), response.failures(), fetchingRound);
}
@Override
public void onFailure(Exception e) {
List failures = new ArrayList<>(nodes.length);
for (final DiscoveryNode node : nodes) {
failures.add(new FailedNodeException(node.getId(), "total failure in fetching", e));
}
processAsyncFetch(null, failures, fetchingRound);
}
});
}
/**
* The result of a fetch operation. Make sure to first check {@link #hasData()} before
* fetching the actual data.
*/
public static class FetchResult {
private final ShardId shardId;
private final Map data;
private final Set ignoreNodes;
public FetchResult(ShardId shardId, Map data, Set ignoreNodes) {
this.shardId = shardId;
this.data = data;
this.ignoreNodes = ignoreNodes;
}
/**
* Does the result actually contain data? If not, then there are on going fetch
* operations happening, and it should wait for it.
*/
public boolean hasData() {
return data != null;
}
/**
* Returns the actual data, note, make sure to check {@link #hasData()} first and
* only use this when there is an actual data.
*/
public Map getData() {
assert data != null : "getData should only be called if there is data to be fetched, please check hasData first";
return this.data;
}
/**
* Process any changes needed to the allocation based on this fetch result.
*/
public void processAllocation(RoutingAllocation allocation) {
for (String ignoreNode : ignoreNodes) {
allocation.addIgnoreShardForNode(shardId, ignoreNode);
}
}
}
/**
* A node entry, holding the state of the fetched data for a specific shard
* for a giving node.
*/
static class NodeEntry {
private final String nodeId;
private boolean fetching;
@Nullable
private T value;
private boolean valueSet;
private Throwable failure;
private long fetchingRound;
NodeEntry(String nodeId) {
this.nodeId = nodeId;
}
String getNodeId() {
return this.nodeId;
}
boolean isFetching() {
return fetching;
}
void markAsFetching(long fetchingRound) {
assert fetching == false : "double marking a node as fetching";
this.fetching = true;
this.fetchingRound = fetchingRound;
}
void doneFetching(T value) {
assert fetching : "setting value but not in fetching mode";
assert failure == null : "setting value when failure already set";
this.valueSet = true;
this.value = value;
this.fetching = false;
}
void doneFetching(Throwable failure) {
assert fetching : "setting value but not in fetching mode";
assert valueSet == false : "setting failure when already set value";
assert failure != null : "setting failure can't be null";
this.failure = failure;
this.fetching = false;
}
void restartFetching() {
assert fetching : "restarting fetching, but not in fetching mode";
assert valueSet == false : "value can't be set when restarting fetching";
assert failure == null : "failure can't be set when restarting fetching";
this.fetching = false;
}
boolean isFailed() {
return failure != null;
}
boolean hasData() {
return valueSet || failure != null;
}
Throwable getFailure() {
assert hasData() : "getting failure when data has not been fetched";
return failure;
}
@Nullable
T getValue() {
assert failure == null : "trying to fetch value, but its marked as failed, check isFailed";
assert valueSet : "value is not set, hasn't been fetched yet";
return value;
}
long getFetchingRound() {
return fetchingRound;
}
}
}