/**
* 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.util.CollectionUtils.computeIfAbsent;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.ConcurrentNavigableMap;
import java.util.concurrent.CopyOnWriteArraySet;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.HRegionInfo;
import org.apache.hadoop.hbase.HRegionLocation;
import org.apache.hadoop.hbase.RegionLocations;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.types.CopyOnWriteArrayMap;
import org.apache.hadoop.hbase.util.Bytes;
/**
* A cache implementation for region locations from meta.
*/
@InterfaceAudience.Private
public class MetaCache {
private static final Log LOG = LogFactory.getLog(MetaCache.class);
/**
* Map of table to table {@link HRegionLocation}s.
*/
private final ConcurrentMap<TableName, ConcurrentNavigableMap<byte[], RegionLocations>>
cachedRegionLocations = new CopyOnWriteArrayMap<>();
// The presence of a server in the map implies it's likely that there is an
// entry in cachedRegionLocations that map to this server; but the absence
// of a server in this map guarantees that there is no entry in cache that
// maps to the absent server.
// The access to this attribute must be protected by a lock on cachedRegionLocations
private final Set<ServerName> cachedServers = new CopyOnWriteArraySet<>();
private final MetricsConnection metrics;
public MetaCache(MetricsConnection metrics) {
this.metrics = metrics;
}
/**
* Search the cache for a location that fits our table and row key.
* Return null if no suitable region is located.
*
* @return Null or region location found in cache.
*/
public RegionLocations getCachedLocation(final TableName tableName, final byte [] row) {
ConcurrentNavigableMap<byte[], RegionLocations> tableLocations =
getTableLocations(tableName);
Entry<byte[], RegionLocations> e = tableLocations.floorEntry(row);
if (e == null) {
if (metrics != null) metrics.incrMetaCacheMiss();
return null;
}
RegionLocations possibleRegion = e.getValue();
// make sure that the end key is greater than the row we're looking
// for, otherwise the row actually belongs in the next region, not
// this one. the exception case is when the endkey is
// HConstants.EMPTY_END_ROW, signifying that the region we're
// checking is actually the last region in the table.
byte[] endKey = possibleRegion.getRegionLocation().getRegionInfo().getEndKey();
// Here we do direct Bytes.compareTo and not doing CellComparator/MetaCellComparator path.
// MetaCellComparator is for comparing against data in META table which need special handling.
// Not doing that is ok for this case because
// 1. We are getting the Region location for the given row in non META tables only. The compare
// checks the given row is within the end key of the found region. So META regions are not
// coming in here.
// 2. Even if META region comes in, its end key will be empty byte[] and so Bytes.equals(endKey,
// HConstants.EMPTY_END_ROW) check itself will pass.
if (Bytes.equals(endKey, HConstants.EMPTY_END_ROW) ||
Bytes.compareTo(endKey, 0, endKey.length, row, 0, row.length) > 0) {
if (metrics != null) metrics.incrMetaCacheHit();
return possibleRegion;
}
// Passed all the way through, so we got nothing - complete cache miss
if (metrics != null) metrics.incrMetaCacheMiss();
return null;
}
/**
* Put a newly discovered HRegionLocation into the cache.
* @param tableName The table name.
* @param source the source of the new location
* @param location the new location
*/
public void cacheLocation(final TableName tableName, final ServerName source,
final HRegionLocation location) {
assert source != null;
byte [] startKey = location.getRegionInfo().getStartKey();
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(tableName);
RegionLocations locations = new RegionLocations(new HRegionLocation[] {location}) ;
RegionLocations oldLocations = tableLocations.putIfAbsent(startKey, locations);
boolean isNewCacheEntry = (oldLocations == null);
if (isNewCacheEntry) {
if (LOG.isTraceEnabled()) {
LOG.trace("Cached location: " + location);
}
addToCachedServers(locations);
return;
}
// If the server in cache sends us a redirect, assume it's always valid.
HRegionLocation oldLocation = oldLocations.getRegionLocation(
location.getRegionInfo().getReplicaId());
boolean force = oldLocation != null && oldLocation.getServerName() != null
&& oldLocation.getServerName().equals(source);
// For redirect if the number is equal to previous
// record, the most common case is that first the region was closed with seqNum, and then
// opened with the same seqNum; hence we will ignore the redirect.
// There are so many corner cases with various combinations of opens and closes that
// an additional counter on top of seqNum would be necessary to handle them all.
RegionLocations updatedLocations = oldLocations.updateLocation(location, false, force);
if (oldLocations != updatedLocations) {
boolean replaced = tableLocations.replace(startKey, oldLocations, updatedLocations);
if (replaced && LOG.isTraceEnabled()) {
LOG.trace("Changed cached location to: " + location);
}
addToCachedServers(updatedLocations);
}
}
/**
* Put a newly discovered HRegionLocation into the cache.
* @param tableName The table name.
* @param locations the new locations
*/
public void cacheLocation(final TableName tableName, final RegionLocations locations) {
byte [] startKey = locations.getRegionLocation().getRegionInfo().getStartKey();
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(tableName);
RegionLocations oldLocation = tableLocations.putIfAbsent(startKey, locations);
boolean isNewCacheEntry = (oldLocation == null);
if (isNewCacheEntry) {
if (LOG.isTraceEnabled()) {
LOG.trace("Cached location: " + locations);
}
addToCachedServers(locations);
return;
}
// merge old and new locations and add it to the cache
// Meta record might be stale - some (probably the same) server has closed the region
// with later seqNum and told us about the new location.
RegionLocations mergedLocation = oldLocation.mergeLocations(locations);
boolean replaced = tableLocations.replace(startKey, oldLocation, mergedLocation);
if (replaced && LOG.isTraceEnabled()) {
LOG.trace("Merged cached locations: " + mergedLocation);
}
addToCachedServers(locations);
}
private void addToCachedServers(RegionLocations locations) {
for (HRegionLocation loc : locations.getRegionLocations()) {
if (loc != null) {
cachedServers.add(loc.getServerName());
}
}
}
/**
* @param tableName
* @return Map of cached locations for passed <code>tableName</code>
*/
private ConcurrentNavigableMap<byte[], RegionLocations> getTableLocations(
final TableName tableName) {
// find the map of cached locations for this table
return computeIfAbsent(cachedRegionLocations, tableName,
() -> new CopyOnWriteArrayMap<>(Bytes.BYTES_COMPARATOR));
}
/**
* Check the region cache to see whether a region is cached yet or not.
* @param tableName tableName
* @param row row
* @return Region cached or not.
*/
public boolean isRegionCached(TableName tableName, final byte[] row) {
RegionLocations location = getCachedLocation(tableName, row);
return location != null;
}
/**
* Return the number of cached region for a table. It will only be called
* from a unit test.
*/
public int getNumberOfCachedRegionLocations(final TableName tableName) {
Map<byte[], RegionLocations> tableLocs = this.cachedRegionLocations.get(tableName);
if (tableLocs == null) {
return 0;
}
int numRegions = 0;
for (RegionLocations tableLoc : tableLocs.values()) {
numRegions += tableLoc.numNonNullElements();
}
return numRegions;
}
/**
* Delete all cached entries.
*/
public void clearCache() {
this.cachedRegionLocations.clear();
this.cachedServers.clear();
}
/**
* Delete all cached entries of a server.
*/
public void clearCache(final ServerName serverName) {
if (!this.cachedServers.contains(serverName)) {
return;
}
boolean deletedSomething = false;
synchronized (this.cachedServers) {
// We block here, because if there is an error on a server, it's likely that multiple
// threads will get the error simultaneously. If there are hundreds of thousand of
// region location to check, it's better to do this only once. A better pattern would
// be to check if the server is dead when we get the region location.
if (!this.cachedServers.contains(serverName)) {
return;
}
for (ConcurrentMap<byte[], RegionLocations> tableLocations : cachedRegionLocations.values()){
for (Entry<byte[], RegionLocations> e : tableLocations.entrySet()) {
RegionLocations regionLocations = e.getValue();
if (regionLocations != null) {
RegionLocations updatedLocations = regionLocations.removeByServer(serverName);
if (updatedLocations != regionLocations) {
if (updatedLocations.isEmpty()) {
deletedSomething |= tableLocations.remove(e.getKey(), regionLocations);
} else {
deletedSomething |= tableLocations.replace(e.getKey(), regionLocations,
updatedLocations);
}
}
}
}
}
this.cachedServers.remove(serverName);
}
if (deletedSomething) {
if (metrics != null) {
metrics.incrMetaCacheNumClearServer();
}
if (LOG.isTraceEnabled()) {
LOG.trace("Removed all cached region locations that map to " + serverName);
}
}
}
/**
* Delete all cached entries of a table.
*/
public void clearCache(final TableName tableName) {
if (LOG.isTraceEnabled()) {
LOG.trace("Removed all cached region locations for table " + tableName);
}
this.cachedRegionLocations.remove(tableName);
}
/**
* Delete a cached location, no matter what it is. Called when we were told to not use cache.
* @param tableName tableName
* @param row
*/
public void clearCache(final TableName tableName, final byte [] row) {
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(tableName);
RegionLocations regionLocations = getCachedLocation(tableName, row);
if (regionLocations != null) {
byte[] startKey = regionLocations.getRegionLocation().getRegionInfo().getStartKey();
boolean removed = tableLocations.remove(startKey, regionLocations);
if (removed) {
if (metrics != null) {
metrics.incrMetaCacheNumClearRegion();
}
if (LOG.isTraceEnabled()) {
LOG.trace("Removed " + regionLocations + " from cache");
}
}
}
}
/**
* Delete a cached location for a table, row and server
*/
public void clearCache(final TableName tableName, final byte [] row, ServerName serverName) {
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(tableName);
RegionLocations regionLocations = getCachedLocation(tableName, row);
if (regionLocations != null) {
RegionLocations updatedLocations = regionLocations.removeByServer(serverName);
if (updatedLocations != regionLocations) {
byte[] startKey = regionLocations.getRegionLocation().getRegionInfo().getStartKey();
boolean removed = false;
if (updatedLocations.isEmpty()) {
removed = tableLocations.remove(startKey, regionLocations);
} else {
removed = tableLocations.replace(startKey, regionLocations, updatedLocations);
}
if (removed) {
if (metrics != null) {
metrics.incrMetaCacheNumClearRegion();
}
if (LOG.isTraceEnabled()) {
LOG.trace("Removed locations of table: " + tableName + " ,row: " + Bytes.toString(row)
+ " mapping to server: " + serverName + " from cache");
}
}
}
}
}
/**
* Deletes the cached location of the region if necessary, based on some error from source.
* @param hri The region in question.
*/
public void clearCache(HRegionInfo hri) {
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(hri.getTable());
RegionLocations regionLocations = tableLocations.get(hri.getStartKey());
if (regionLocations != null) {
HRegionLocation oldLocation = regionLocations.getRegionLocation(hri.getReplicaId());
if (oldLocation == null) return;
RegionLocations updatedLocations = regionLocations.remove(oldLocation);
boolean removed;
if (updatedLocations != regionLocations) {
if (updatedLocations.isEmpty()) {
removed = tableLocations.remove(hri.getStartKey(), regionLocations);
} else {
removed = tableLocations.replace(hri.getStartKey(), regionLocations, updatedLocations);
}
if (removed) {
if (metrics != null) {
metrics.incrMetaCacheNumClearRegion();
}
if (LOG.isTraceEnabled()) {
LOG.trace("Removed " + oldLocation + " from cache");
}
}
}
}
}
public void clearCache(final HRegionLocation location) {
if (location == null) {
return;
}
TableName tableName = location.getRegionInfo().getTable();
ConcurrentMap<byte[], RegionLocations> tableLocations = getTableLocations(tableName);
RegionLocations regionLocations = tableLocations.get(location.getRegionInfo().getStartKey());
if (regionLocations != null) {
RegionLocations updatedLocations = regionLocations.remove(location);
boolean removed;
if (updatedLocations != regionLocations) {
if (updatedLocations.isEmpty()) {
removed = tableLocations.remove(location.getRegionInfo().getStartKey(), regionLocations);
} else {
removed = tableLocations.replace(location.getRegionInfo().getStartKey(), regionLocations,
updatedLocations);
}
if (removed) {
if (metrics != null) {
metrics.incrMetaCacheNumClearRegion();
}
if (LOG.isTraceEnabled()) {
LOG.trace("Removed " + location + " from cache");
}
}
}
}
}
}