saintstack commented on a change in pull request #2584:
URL: https://github.com/apache/hbase/pull/2584#discussion_r517036330
##########
File path:
hbase-client/src/main/java/org/apache/hadoop/hbase/client/AsyncNonMetaRegionLocator.java
##########
@@ -433,9 +474,24 @@ private void locateInMeta(TableName tableName,
LocateRequest req) {
Scan scan = new Scan().withStartRow(metaStartKey).withStopRow(metaStopKey,
true)
.addFamily(HConstants.CATALOG_FAMILY).setReversed(true).setCaching(locatePrefetchLimit)
.setReadType(ReadType.PREAD);
- if (useMetaReplicas) {
- scan.setConsistency(Consistency.TIMELINE);
+
+ switch (this.metaReplicaMode) {
+ case LoadBalance:
+ int metaReplicaId = this.metaReplicaSelector.select(tableName,
req.row, req.locateType);
+ if (metaReplicaId != RegionInfo.DEFAULT_REPLICA_ID) {
+ // If the selector gives a non-primary meta replica region, then go
with it.
+ // Otherwise, just go to primary in non-hedgedRead mode.
+ scan.setConsistency(Consistency.TIMELINE);
+ scan.setReplicaId(metaReplicaId);
+ }
+ break;
+ case HedgedRead:
+ scan.setConsistency(Consistency.TIMELINE);
+ break;
+ default:
+ // do nothing
Review comment:
Did you file one @huaxiangsun ?
##########
File path:
hbase-client/src/main/java/org/apache/hadoop/hbase/client/CatalogReplicaMode.java
##########
@@ -0,0 +1,64 @@
+/**
+ * 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.hbase.client;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+/**
+ * <p>There are two modes with catalog replica support. </p>
+ *
+ * <ol>
+ * <li>HEDGED_READ - Client sends requests to the primary region first,
within a
+ * configured amount of time, if there is no response coming
back,
+ * client sends requests to all replica regions and takes the
first
+ * response. </li>
+ *
+ * <li>LOAD_BALANCE - Client sends requests to replica regions in a
round-robin mode,
+ * if results from replica regions are stale, next time,
client sends requests for
+ * these stale locations to the primary region. In this mode,
scan
+ * requests are load balanced across all replica regions.</li>
+ * </ol>
+ */
[email protected]
+enum CatalogReplicaMode {
+ NONE {
+ @Override
+ public String toString() {
+ return "None";
+ }
+ },
+ HEDGED_READ {
+ @Override
+ public String toString() {
+ return "HedgedRead";
+ }
+ },
+ LOAD_BALANCE {
+ @Override
+ public String toString() {
+ return "LoadBalance";
+ }
+ };
+
+ public static CatalogReplicaMode fromString(final String value) {
+ for(CatalogReplicaMode mode : values()) {
+ if (mode.toString().equalsIgnoreCase(value)) {
Review comment:
Good that you ignore case.
##########
File path:
hbase-client/src/main/java/org/apache/hadoop/hbase/client/CatalogReplicaLoadBalanceSimpleSelector.java
##########
@@ -0,0 +1,302 @@
+/**
+ * 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.hbase.client;
+
+import static org.apache.hadoop.hbase.client.ConnectionUtils.isEmptyStopRow;
+import static org.apache.hadoop.hbase.util.Bytes.BYTES_COMPARATOR;
+import static org.apache.hadoop.hbase.util.ConcurrentMapUtils.computeIfAbsent;
+import java.util.Iterator;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.ConcurrentNavigableMap;
+import java.util.concurrent.ConcurrentSkipListMap;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.function.IntSupplier;
+import org.apache.commons.lang3.builder.ToStringBuilder;
+import org.apache.hadoop.hbase.HRegionLocation;
+import org.apache.hadoop.hbase.ScheduledChore;
+import org.apache.hadoop.hbase.Stoppable;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.hadoop.hbase.util.Bytes;
+import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * <p>CatalogReplicaLoadBalanceReplicaSimpleSelector implements a simple
catalog replica load balancing
+ * algorithm. It maintains a stale location cache for each table. Whenever
client looks up location,
+ * it first check if the row is the stale location cache. If yes, the location
from
+ * catalog replica is stale, it will go to the primary region to look up
update-to-date location;
+ * otherwise, it will randomly pick up a replica region for lookup. When
clients receive
+ * RegionNotServedException from region servers, it will add these region
locations to the stale
+ * location cache. The stale cache will be cleaned up periodically by a
chore.</p>
+ *
+ * It follows a simple algorithm to choose a replica to go:
+ *
+ * <ol>
+ * <li>If there is no stale location entry for rows it looks up, it will
randomly
+ * pick a replica region to do lookup. </li>
+ * <li>If the location from the replica region is stale, client gets
RegionNotServedException
+ * from region server, in this case, it will create
StaleLocationCacheEntry in
+ * CatalogReplicaLoadBalanceReplicaSimpleSelector.</li>
+ * <li>When client tries to do location lookup, it checks StaleLocationCache
first for rows it
+ * tries to lookup, if entry exists, it will go with primary meta region
to do lookup;
+ * otherwise, it will follow step 1.</li>
+ * <li>A chore will periodically run to clean up cache entries in the
StaleLocationCache.</li>
+ * </ol>
+ */
+class CatalogReplicaLoadBalanceSimpleSelector implements
+ CatalogReplicaLoadBalanceSelector, Stoppable {
+ private static final Logger LOG =
+ LoggerFactory.getLogger(CatalogReplicaLoadBalanceSimpleSelector.class);
+ private final long STALE_CACHE_TIMEOUT_IN_MILLISECONDS = 3000; // 3 seconds
+ private final int STALE_CACHE_CLEAN_CHORE_INTERVAL_IN_MILLISECONDS = 1500;
// 1.5 seconds
+ private final int REFRESH_REPLICA_COUNT_CHORE_INTERVAL_IN_MILLISECONDS =
60000; // 1 minute
+
+ /**
+ * StaleLocationCacheEntry is the entry when a stale location is reported by
an client.
+ */
+ private static final class StaleLocationCacheEntry {
+ // replica id where the stale location comes from.
+ private final int fromReplicaId;
+
+ // timestamp in milliseconds
+ private final long timestamp;
+
+ private final byte[] endKey;
+
+ StaleLocationCacheEntry(final int metaReplicaId, final byte[] endKey) {
+ this.fromReplicaId = metaReplicaId;
+ this.endKey = endKey;
+ timestamp = EnvironmentEdgeManager.currentTime();
+ }
+
+ public byte[] getEndKey() {
+ return this.endKey;
+ }
+
+ public int getFromReplicaId() {
+ return this.fromReplicaId;
+ }
+ public long getTimestamp() {
+ return this.timestamp;
+ }
+
+ @Override
+ public String toString() {
+ return new ToStringBuilder(this)
+ .append("endKey", endKey)
+ .append("fromReplicaId", fromReplicaId)
+ .append("timestamp", timestamp)
+ .toString();
+ }
+ }
+
+ private final ConcurrentMap<TableName, ConcurrentNavigableMap<byte[],
StaleLocationCacheEntry>>
+ staleCache = new ConcurrentHashMap<>();
+ private volatile int numOfReplicas;
+ private final AsyncConnectionImpl conn;
+ private final TableName tableName;
+ private final IntSupplier getNumOfReplicas;
+ private volatile boolean isStopped = false;
+
+ CatalogReplicaLoadBalanceSimpleSelector(TableName tableName,
AsyncConnectionImpl conn,
+ IntSupplier getNumOfReplicas) {
+ this.conn = conn;
+ this.tableName = tableName;
+ this.getNumOfReplicas = getNumOfReplicas;
+
+ // This numOfReplicas is going to be lazy initialized.
+ this.numOfReplicas = -1;
+ // Start chores
+ this.conn.getChoreService().scheduleChore(getCacheCleanupChore(this));
+
this.conn.getChoreService().scheduleChore(getRefreshReplicaCountChore(this));
+ }
+
+ /**
+ * When a client runs into RegionNotServingException, it will call this
method to
+ * update Selector's internal state.
+ * @param loc the location which causes exception.
+ * @param fromReplicaId the replica id where the stale location comes from.
+ */
+ public void onError(HRegionLocation loc, int fromReplicaId) {
+ ConcurrentNavigableMap<byte[], StaleLocationCacheEntry> tableCache =
+ computeIfAbsent(staleCache, loc.getRegion().getTable(),
+ () -> new ConcurrentSkipListMap<>(BYTES_COMPARATOR));
+ byte[] startKey = loc.getRegion().getStartKey();
+ tableCache.putIfAbsent(startKey,
+ new StaleLocationCacheEntry(fromReplicaId, loc.getRegion().getEndKey()));
+ LOG.debug("Add entry to stale cache for table {} with startKey {}, {}",
+ loc.getRegion().getTable(), startKey, loc.getRegion().getEndKey());
+ }
+
+ /**
+ * Select an random replica id. In case there is no replica region
configured, return
+ * the primary replica id.
+ * @return Replica id
+ */
+ private int getRandomReplicaId() {
+ int cachedNumOfReplicas = this.numOfReplicas;
+ if (cachedNumOfReplicas < 0) {
+ cachedNumOfReplicas = refreshCatalogReplicaCount();
+ this.numOfReplicas = cachedNumOfReplicas;
+ }
+ // In case of no replica configured, return the primary region id.
+ if (cachedNumOfReplicas <= 1) {
+ return RegionInfo.DEFAULT_REPLICA_ID;
+ }
+ return 1 + ThreadLocalRandom.current().nextInt(cachedNumOfReplicas - 1);
+ }
+
+ /**
+ * When it looks up a location, it will call this method to find a replica
region to go.
+ * For a normal case, > 99% of region locations from catalog/meta replica
will be up to date.
+ * In extreme cases such as region server crashes, it will depends on how
fast replication
+ * catches up.
+ *
+ * @param tablename table name it looks up
+ * @param row key it looks up.
+ * @param locateType locateType, Only BEFORE and CURRENT will be passed in.
+ * @return catalog replica id
+ */
+ public int select(final TableName tablename, final byte[] row,
+ final RegionLocateType locateType) {
+ ConcurrentNavigableMap<byte[], StaleLocationCacheEntry> tableCache =
staleCache.get(tablename);
+
+ // If there is no entry in StaleCache, select a random replica id.
+ if (tableCache == null) {
+ return getRandomReplicaId();
+ }
+
+ Map.Entry<byte[], StaleLocationCacheEntry> entry;
+ boolean isEmptyStopRow = isEmptyStopRow(row);
+ // Only BEFORE and CURRENT are passed in.
+ if (locateType == RegionLocateType.BEFORE) {
+ entry = isEmptyStopRow ? tableCache.lastEntry() :
tableCache.lowerEntry(row);
+ } else {
+ entry = tableCache.floorEntry(row);
+ }
+
+ // It is not in the stale cache, return a random replica id.
+ if (entry == null) {
+ return getRandomReplicaId();
+ }
+
+ // The entry here is a possible match for the location. Check if the entry
times out first as
+ // long comparing is faster than comparing byte arrays(in most cases). It
could remove
+ // stale entries faster. If the possible match entry does not time out, it
will check if
+ // the entry is a match for the row passed in and select the replica id
accordingly.
+ if ((EnvironmentEdgeManager.currentTime() -
entry.getValue().getTimestamp()) >=
+ STALE_CACHE_TIMEOUT_IN_MILLISECONDS) {
+ LOG.debug("Entry for table {} with startKey {}, {} times out",
tablename, entry.getKey(),
+ entry);
+ tableCache.remove(entry.getKey());
+ return getRandomReplicaId();
+ }
+
+ byte[] endKey = entry.getValue().getEndKey();
+
+ // The following logic is borrowed from AsyncNonMetaRegionLocator.
+ if (isEmptyStopRow(endKey)) {
+ LOG.debug("Lookup {} goes to primary region", row);
+ return RegionInfo.DEFAULT_REPLICA_ID;
+ }
+
+ if (locateType == RegionLocateType.BEFORE) {
+ if (!isEmptyStopRow && Bytes.compareTo(endKey, row) >= 0) {
+ LOG.debug("Lookup {} goes to primary meta", row);
+ return RegionInfo.DEFAULT_REPLICA_ID;
+ }
+ } else {
+ if (Bytes.compareTo(row, endKey) < 0) {
+ LOG.debug("Lookup {} goes to primary meta", row);
+ return RegionInfo.DEFAULT_REPLICA_ID;
+ }
+ }
+
+ // Not in stale cache, return a random replica id.
+ return getRandomReplicaId();
+ }
+
+ @Override
+ public void stop(String why) {
Review comment:
So, implements Stoppable rather than do what the likes of AuthUtil does
where it does createDummyStoppable and then has an internal do-nothing
Stoppable? Makes sense.
Perhaps add comment that it is a do-nothing stop required by ScheduledChore
impls. s/isStopped/stopped/
##########
File path:
hbase-client/src/main/java/org/apache/hadoop/hbase/client/CatalogReplicaLoadBalanceSelector.java
##########
@@ -0,0 +1,47 @@
+/**
+ * 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.hbase.client;
+
+import org.apache.hadoop.hbase.HRegionLocation;
+import org.apache.hadoop.hbase.TableName;
+import org.apache.yetus.audience.InterfaceAudience;
+
+/**
+ * A Catalog replica selector decides which catalog replica to go for read
requests when it is
+ * configured as CatalogReplicaMode.LoadBalance.
+ */
[email protected]
+interface CatalogReplicaLoadBalanceSelector {
+
+ /**
+ * This method is called when input location is stale, i.e, when clients run
into
+ * org.apache.hadoop.hbase.NotServingRegionException.
+ * @param loc stale location
+ */
+ void onError(HRegionLocation loc);
+
+ /**
+ * Select a catalog replica region where client go to loop up the input row
key.
+ *
+ * @param tablename table name
+ * @param row key to look up
+ * @param locateType locate type
+ * @return replica id
+ */
+ int select(TableName tablename, byte[] row, RegionLocateType locateType);
+}
Review comment:
Good
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