/**
* 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.cassandra.service;
import java.io.*;
import java.net.InetAddress;
import java.security.MessageDigest;
import java.util.*;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;
import com.google.common.base.Objects;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.apache.cassandra.concurrent.Stage;
import org.apache.cassandra.concurrent.StageManager;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.ColumnFamilyStore;
import org.apache.cassandra.db.CompactionManager;
import org.apache.cassandra.db.DecoratedKey;
import org.apache.cassandra.db.Table;
import org.apache.cassandra.dht.Range;
import org.apache.cassandra.dht.Token;
import org.apache.cassandra.gms.FailureDetector;
import org.apache.cassandra.io.AbstractCompactedRow;
import org.apache.cassandra.io.ICompactSerializer;
import org.apache.cassandra.io.sstable.SSTableReader;
import org.apache.cassandra.net.CompactEndpointSerializationHelper;
import org.apache.cassandra.net.IVerbHandler;
import org.apache.cassandra.net.Message;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.streaming.StreamIn;
import org.apache.cassandra.streaming.StreamOut;
import org.apache.cassandra.streaming.StreamOutSession;
import org.apache.cassandra.utils.*;
/**
* AntiEntropyService encapsulates "validating" (hashing) individual column families,
* exchanging MerkleTrees with remote nodes via a TreeRequest/Response conversation,
* and then triggering repairs for disagreeing ranges.
*
* Every Tree conversation has an 'initiator', where valid trees are sent after generation
* and where the local and remote tree will rendezvous in rendezvous(cf, endpoint, tree).
* Once the trees rendezvous, a Differencer is executed and the service can trigger repairs
* for disagreeing ranges.
*
* Tree comparison and repair triggering occur in the single threaded Stage.ANTIENTROPY.
*
* The steps taken to enact a repair are as follows:
* 1. A major compaction is triggered via nodeprobe:
* * Nodeprobe sends TreeRequest messages to all neighbors of the target node: when a node
* receives a TreeRequest, it will perform a readonly compaction to immediately validate
* the column family.
* 2. The compaction process validates the column family by:
* * Calling Validator.prepare(), which samples the column family to determine key distribution,
* * Calling Validator.add() in order for every row in the column family,
* * Calling Validator.complete() to indicate that all rows have been added.
* * Calling complete() indicates that a valid MerkleTree has been created for the column family.
* * The valid tree is returned to the requesting node via a TreeResponse.
* 3. When a node receives a TreeResponse, it passes the tree to rendezvous(), which checks for trees to
* rendezvous with / compare to:
* * If the tree is local, it is cached, and compared to any trees that were received from neighbors.
* * If the tree is remote, it is immediately compared to a local tree if one is cached. Otherwise,
* the remote tree is stored until a local tree can be generated.
* * A Differencer object is enqueued for each comparison.
* 4. Differencers are executed in Stage.ANTIENTROPY, to compare the two trees, and perform repair via the
* streaming api.
*/
public class AntiEntropyService
{
private static final Logger logger = LoggerFactory.getLogger(AntiEntropyService.class);
// singleton enforcement
public static final AntiEntropyService instance = new AntiEntropyService();
// timeout for outstanding requests (48 hours)
public final static long REQUEST_TIMEOUT = 48*60*60*1000;
/**
* Map of outstanding sessions to requests. Once both trees reach the rendezvous, the local node
* will queue a Differencer to compare them.
*
* This map is only accessed from Stage.ANTIENTROPY, so it is not synchronized.
*/
private final ExpiringMap<String, Map<TreeRequest, TreePair>> requests;
/**
* A map of repair session ids to a Queue of TreeRequests that have been performed since the session was started.
*/
private final ConcurrentMap<String, RepairSession.Callback> sessions;
/**
* Protected constructor. Use AntiEntropyService.instance.
*/
protected AntiEntropyService()
{
requests = new ExpiringMap<String, Map<TreeRequest, TreePair>>(REQUEST_TIMEOUT);
sessions = new ConcurrentHashMap<String, RepairSession.Callback>();
}
/**
* Requests repairs for the given table and column families, and blocks until all repairs have been completed.
* TODO: Should add retries: if nodes go offline before they respond to the requests, this could block forever.
*/
public RepairSession getRepairSession(String tablename, String... cfnames)
{
return new RepairSession(tablename, cfnames);
}
/**
* Called by Differencer when a full repair round trip has been completed between the given CF and endpoints.
*/
void completedRequest(TreeRequest request)
{
// indicate to the waiting session that this request completed
sessions.get(request.sessionid).completed(request);
}
/**
* Returns the map of waiting rendezvous endpoints to trees for the given session.
* Should only be called within Stage.ANTIENTROPY.
*/
private Map<TreeRequest, TreePair> rendezvousPairs(String sessionid)
{
Map<TreeRequest, TreePair> ctrees = requests.get(sessionid);
if (ctrees == null)
{
ctrees = new HashMap<TreeRequest, TreePair>();
requests.put(sessionid, ctrees);
}
return ctrees;
}
/**
* Return all of the neighbors with whom we share data.
*/
static Set<InetAddress> getNeighbors(String table)
{
StorageService ss = StorageService.instance;
Set<InetAddress> neighbors = new HashSet<InetAddress>();
Map<Range, List<InetAddress>> replicaSets = ss.getRangeToAddressMap(table);
for (Range range : ss.getLocalRanges(table))
{
// for every range stored locally (replica or original) collect neighbors storing copies
neighbors.addAll(replicaSets.get(range));
}
neighbors.remove(FBUtilities.getLocalAddress());
return neighbors;
}
/**
* Register a tree for the given request to be compared to the appropriate trees in Stage.ANTIENTROPY when they become available.
*/
private void rendezvous(TreeRequest request, MerkleTree tree)
{
InetAddress LOCAL = FBUtilities.getLocalAddress();
// the rendezvous pairs for this session
Map<TreeRequest, TreePair> ctrees = rendezvousPairs(request.sessionid);
List<Differencer> differencers = new ArrayList<Differencer>();
if (LOCAL.equals(request.endpoint))
{
// we're registering a local tree: rendezvous with remote requests for the session
for (InetAddress neighbor : getNeighbors(request.cf.left))
{
TreeRequest remotereq = new TreeRequest(request.sessionid, neighbor, request.cf);
TreePair waiting = ctrees.remove(remotereq);
if (waiting != null && waiting.right != null)
{
// the neighbor beat us to the rendezvous: queue differencing
// FIXME: Differencer should take a TreeRequest
differencers.add(new Differencer(remotereq, tree, waiting.right));
continue;
}
// else, the local tree is first to the rendezvous: store and wait
ctrees.put(remotereq, new TreePair(tree, null));
logger.debug("Stored local tree for " + request + " to wait for " + remotereq);
}
}
else
{
// we're registering a remote tree: rendezvous with the local tree
TreePair waiting = ctrees.remove(request);
if (waiting != null && waiting.left != null)
{
// the local tree beat us to the rendezvous: queue differencing
differencers.add(new Differencer(request, waiting.left, tree));
}
else
{
// else, the remote tree is first to the rendezvous: store and wait
ctrees.put(request, new TreePair(null, tree));
logger.debug("Stored remote tree for " + request + " to wait for local tree.");
}
}
for (Differencer differencer : differencers)
{
logger.info("Queueing comparison " + differencer);
StageManager.getStage(Stage.ANTI_ENTROPY).execute(differencer);
}
}
/**
* Requests a tree from the given node, and returns the request that was sent.
*/
TreeRequest request(String sessionid, InetAddress remote, String ksname, String cfname)
{
TreeRequest request = new TreeRequest(sessionid, remote, new CFPair(ksname, cfname));
MessagingService.instance().sendOneWay(TreeRequestVerbHandler.makeVerb(request), remote);
return request;
}
/**
* Responds to the node that requested the given valid tree.
* @param validator A locally generated validator
* @param local localhost (parameterized for testing)
*/
void respond(Validator validator, InetAddress local)
{
MessagingService ms = MessagingService.instance();
try
{
Message message = TreeResponseVerbHandler.makeVerb(local, validator);
logger.info("Sending AEService tree for " + validator.request);
ms.sendOneWay(message, validator.request.endpoint);
}
catch (Exception e)
{
logger.error("Could not send valid tree for request " + validator.request, e);
}
}
/**
* A Strategy to handle building and validating a merkle tree for a column family.
*
* Lifecycle:
* 1. prepare() - Initialize tree with samples.
* 2. add() - 0 or more times, to add hashes to the tree.
* 3. complete() - Enqueues any operations that were blocked waiting for a valid tree.
*/
public static class Validator implements Runnable
{
public final TreeRequest request;
public final MerkleTree tree;
// the minimum token sorts first, but falls into the last range
private transient List<MerkleTree.RowHash> minrows;
// null when all rows with the min token have been consumed
private transient Token mintoken;
private transient long validated;
private transient MerkleTree.TreeRange range;
private transient MerkleTree.TreeRangeIterator ranges;
private transient DecoratedKey lastKey;
public final static MerkleTree.RowHash EMPTY_ROW = new MerkleTree.RowHash(null, new byte[0]);
Validator(TreeRequest request)
{
this(request,
// TODO: memory usage (maxsize) should either be tunable per
// CF, globally, or as shared for all CFs in a cluster
new MerkleTree(DatabaseDescriptor.getPartitioner(), MerkleTree.RECOMMENDED_DEPTH, (int)Math.pow(2, 15)));
}
Validator(TreeRequest request, MerkleTree tree)
{
this.request = request;
this.tree = tree;
minrows = new ArrayList<MerkleTree.RowHash>();
mintoken = null;
validated = 0;
range = null;
ranges = null;
}
public void prepare(ColumnFamilyStore cfs)
{
List<DecoratedKey> keys = new ArrayList<DecoratedKey>();
for (DecoratedKey sample : cfs.allKeySamples())
keys.add(sample);
if (keys.isEmpty())
{
// use an even tree distribution
tree.init();
}
else
{
int numkeys = keys.size();
Random random = new Random();
// sample the column family using random keys from the index
while (true)
{
DecoratedKey dk = keys.get(random.nextInt(numkeys));
if (!tree.split(dk.token))
break;
}
}
logger.debug("Prepared AEService tree of size " + tree.size() + " for " + request);
mintoken = tree.partitioner().getMinimumToken();
ranges = tree.invalids(new Range(mintoken, mintoken));
}
/**
* Called (in order) for every row present in the CF.
* Hashes the row, and adds it to the tree being built.
*
* There are four possible cases:
* 1. Token is greater than range.right (we haven't generated a range for it yet),
* 2. Token is less than/equal to range.left (the range was valid),
* 3. Token is contained in the range (the range is in progress),
* 4. No more invalid ranges exist.
*
* TODO: Because we only validate completely empty trees at the moment, we
* do not bother dealing with case 2 and case 4 should result in an error.
*
* Additionally, there is a special case for the minimum token, because
* although it sorts first, it is contained in the last possible range.
*
* @param row The row.
*/
public void add(AbstractCompactedRow row)
{
assert lastKey == null || lastKey.compareTo(row.key) < 0
: "row " + row.key + " received out of order wrt " + lastKey;
lastKey = row.key;
if (mintoken != null)
{
assert ranges != null : "Validator was not prepared()";
// check for the minimum token special case
if (row.key.token.compareTo(mintoken) == 0)
{
// and store it to be appended when we complete
minrows.add(rowHash(row));
return;
}
mintoken = null;
}
if (range == null)
range = ranges.next();
// generate new ranges as long as case 1 is true
while (!range.contains(row.key.token))
{
// add the empty hash, and move to the next range
range.addHash(EMPTY_ROW);
range = ranges.next();
}
// case 3 must be true: mix in the hashed row
range.addHash(rowHash(row));
}
private MerkleTree.RowHash rowHash(AbstractCompactedRow row)
{
validated++;
// MerkleTree uses XOR internally, so we want lots of output bits here
MessageDigest digest = FBUtilities.newMessageDigest("SHA-256");
row.update(digest);
return new MerkleTree.RowHash(row.key.token, digest.digest());
}
/**
* Registers the newly created tree for rendezvous in Stage.ANTIENTROPY.
*/
public void complete()
{
assert ranges != null : "Validator was not prepared()";
if (range != null)
range.addHash(EMPTY_ROW);
while (ranges.hasNext())
{
range = ranges.next();
range.addHash(EMPTY_ROW);
}
// add rows with the minimum token to the final range
if (!minrows.isEmpty())
for (MerkleTree.RowHash minrow : minrows)
range.addHash(minrow);
StageManager.getStage(Stage.ANTI_ENTROPY).execute(this);
logger.debug("Validated " + validated + " rows into AEService tree for " + request);
}
/**
* Called after the validation lifecycle to respond with the now valid tree. Runs in Stage.ANTIENTROPY.
*
* @return A meaningless object.
*/
public void run()
{
// respond to the request that triggered this validation
AntiEntropyService.instance.respond(this, FBUtilities.getLocalAddress());
}
}
/**
* Runs on the node that initiated a request to compare two trees, and launch repairs for disagreeing ranges.
*/
public static class Differencer implements Runnable
{
public final TreeRequest request;
public final MerkleTree ltree;
public final MerkleTree rtree;
public final List<Range> differences;
public Differencer(TreeRequest request, MerkleTree ltree, MerkleTree rtree)
{
this.request = request;
this.ltree = ltree;
this.rtree = rtree;
differences = new ArrayList<Range>();
}
/**
* Compares our trees, and triggers repairs for any ranges that mismatch.
*/
public void run()
{
InetAddress local = FBUtilities.getLocalAddress();
StorageService ss = StorageService.instance;
// restore partitioners (in case we were serialized)
if (ltree.partitioner() == null)
ltree.partitioner(StorageService.getPartitioner());
if (rtree.partitioner() == null)
rtree.partitioner(StorageService.getPartitioner());
// determine the ranges where responsibility overlaps
Set<Range> interesting = new HashSet(ss.getRangesForEndpoint(request.cf.left, local));
interesting.retainAll(ss.getRangesForEndpoint(request.cf.left, request.endpoint));
// compare trees, and collect interesting differences
for (MerkleTree.TreeRange diff : MerkleTree.difference(ltree, rtree))
for (Range localrange: interesting)
differences.addAll(diff.intersectionWith(localrange));
// choose a repair method based on the significance of the difference
String format = "Endpoints " + local + " and " + request.endpoint + " %s for " + request.cf;
if (differences.isEmpty())
{
logger.info(String.format(format, "are consistent"));
AntiEntropyService.instance.completedRequest(request);
return;
}
// non-0 difference: perform streaming repair
logger.info(String.format(format, "have " + differences.size() + " range(s) out of sync"));
try
{
performStreamingRepair();
}
catch(IOException e)
{
throw new RuntimeException(e);
}
}
/**
* Starts sending/receiving our list of differences to/from the remote endpoint: creates a callback
* that will be called out of band once the streams complete.
*/
void performStreamingRepair() throws IOException
{
logger.info("Performing streaming repair of " + differences.size() + " ranges for " + request);
ColumnFamilyStore cfstore = Table.open(request.cf.left).getColumnFamilyStore(request.cf.right);
try
{
List<Range> ranges = new ArrayList<Range>(differences);
Collection<SSTableReader> sstables = cfstore.getSSTables();
Callback callback = new Callback();
// send ranges to the remote node
StreamOutSession outsession = StreamOutSession.create(request.cf.left, request.endpoint, callback);
StreamOut.transferSSTables(outsession, sstables, ranges);
// request ranges from the remote node
StreamIn.requestRanges(request.endpoint, request.cf.left, ranges, callback);
}
catch(Exception e)
{
throw new IOException("Streaming repair failed.", e);
}
}
public String toString()
{
return "#<Differencer " + request + ">";
}
/**
* When a repair is necessary, this callback is created to wait for the inbound
* and outbound streams to complete.
*/
class Callback extends WrappedRunnable
{
// we expect one callback for the receive, and one for the send
private final AtomicInteger outstanding = new AtomicInteger(2);
protected void runMayThrow() throws Exception
{
if (outstanding.decrementAndGet() > 0)
// waiting on more calls
return;
// all calls finished successfully
logger.info("Finished streaming repair for " + request);
AntiEntropyService.instance.completedRequest(request);
}
}
}
/**
* Handler for requests from remote nodes to generate a valid tree.
* The payload is a CFPair representing the columnfamily to validate.
*/
public static class TreeRequestVerbHandler implements IVerbHandler, ICompactSerializer<TreeRequest>
{
public static final TreeRequestVerbHandler SERIALIZER = new TreeRequestVerbHandler();
static Message makeVerb(TreeRequest request)
{
try
{
ByteArrayOutputStream bos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(bos);
SERIALIZER.serialize(request, dos);
return new Message(FBUtilities.getLocalAddress(), StorageService.Verb.TREE_REQUEST, bos.toByteArray());
}
catch(IOException e)
{
throw new RuntimeException(e);
}
}
public void serialize(TreeRequest request, DataOutputStream dos) throws IOException
{
dos.writeUTF(request.sessionid);
CompactEndpointSerializationHelper.serialize(request.endpoint, dos);
dos.writeUTF(request.cf.left);
dos.writeUTF(request.cf.right);
}
public TreeRequest deserialize(DataInputStream dis) throws IOException
{
return new TreeRequest(dis.readUTF(),
CompactEndpointSerializationHelper.deserialize(dis),
new CFPair(dis.readUTF(), dis.readUTF()));
}
/**
* Trigger a validation compaction which will return the tree upon completion.
*/
public void doVerb(Message message, String id)
{
byte[] bytes = message.getMessageBody();
DataInputStream buffer = new DataInputStream(new ByteArrayInputStream(bytes));
try
{
TreeRequest remotereq = this.deserialize(buffer);
TreeRequest request = new TreeRequest(remotereq.sessionid, message.getFrom(), remotereq.cf);
// trigger readonly-compaction
ColumnFamilyStore store = Table.open(request.cf.left).getColumnFamilyStore(request.cf.right);
Validator validator = new Validator(request);
logger.debug("Queueing validation compaction for " + request);
CompactionManager.instance.submitValidation(store, validator);
}
catch (IOException e)
{
throw new IOError(e);
}
}
}
/**
* Handler for responses from remote nodes which contain a valid tree.
* The payload is a completed Validator object from the remote endpoint.
*/
public static class TreeResponseVerbHandler implements IVerbHandler, ICompactSerializer<Validator>
{
public static final TreeResponseVerbHandler SERIALIZER = new TreeResponseVerbHandler();
static Message makeVerb(InetAddress local, Validator validator)
{
try
{
ByteArrayOutputStream bos = new ByteArrayOutputStream();
DataOutputStream dos = new DataOutputStream(bos);
SERIALIZER.serialize(validator, dos);
return new Message(local, StorageService.Verb.TREE_RESPONSE, bos.toByteArray());
}
catch(IOException e)
{
throw new RuntimeException(e);
}
}
public void serialize(Validator v, DataOutputStream dos) throws IOException
{
TreeRequestVerbHandler.SERIALIZER.serialize(v.request, dos);
ObjectOutputStream oos = new ObjectOutputStream(dos);
oos.writeObject(v.tree);
oos.flush();
}
public Validator deserialize(DataInputStream dis) throws IOException
{
final TreeRequest request = TreeRequestVerbHandler.SERIALIZER.deserialize(dis);
ObjectInputStream ois = new ObjectInputStream(dis);
try
{
return new Validator(request, (MerkleTree)ois.readObject());
}
catch(Exception e)
{
throw new RuntimeException(e);
}
}
public void doVerb(Message message, String id)
{
byte[] bytes = message.getMessageBody();
DataInputStream buffer = new DataInputStream(new ByteArrayInputStream(bytes));
try
{
// deserialize the remote tree, and register it
Validator response = this.deserialize(buffer);
TreeRequest request = new TreeRequest(response.request.sessionid, message.getFrom(), response.request.cf);
AntiEntropyService.instance.rendezvous(request, response.tree);
}
catch (IOException e)
{
throw new IOError(e);
}
}
}
/**
* A tuple of table and cf.
*/
static class CFPair extends Pair<String,String>
{
public CFPair(String table, String cf)
{
super(table, cf);
assert table != null && cf != null;
}
}
/**
* A tuple of a local and remote tree.
*/
static class TreePair extends Pair<MerkleTree,MerkleTree>
{
public TreePair(MerkleTree local, MerkleTree remote)
{
super(local, remote);
}
}
/**
* A triple of table, cf and address that represents a location we have an outstanding TreeRequest for.
*/
public static class TreeRequest
{
public final String sessionid;
public final InetAddress endpoint;
public final CFPair cf;
public TreeRequest(String sessionid, InetAddress endpoint, CFPair cf)
{
this.sessionid = sessionid;
this.endpoint = endpoint;
this.cf = cf;
}
@Override
public final int hashCode()
{
return Objects.hashCode(sessionid, endpoint, cf);
}
@Override
public final boolean equals(Object o)
{
if(!(o instanceof TreeRequest))
return false;
TreeRequest that = (TreeRequest)o;
// handles nulls properly
return Objects.equal(sessionid, that.sessionid) && Objects.equal(endpoint, that.endpoint) && Objects.equal(cf, that.cf);
}
@Override
public String toString()
{
return "#<TreeRequest " + sessionid + ", " + endpoint + ", " + cf + ">";
}
}
/**
* Triggers repairs with all neighbors for the given table and cfs. Typical lifecycle is: start() then join().
* Executed in client threads.
*/
class RepairSession extends Thread
{
private final String tablename;
private final String[] cfnames;
private final SimpleCondition requestsMade;
private final ConcurrentHashMap<TreeRequest,Object> requests;
public RepairSession(String tablename, String... cfnames)
{
super("manual-repair-" + UUID.randomUUID());
this.tablename = tablename;
this.cfnames = cfnames;
this.requestsMade = new SimpleCondition();
this.requests = new ConcurrentHashMap<TreeRequest,Object>();
}
/**
* Waits until all requests for the session have been sent out: to wait for the session to end, call join().
*/
public void blockUntilRunning() throws InterruptedException
{
requestsMade.await();
}
@Override
public void run()
{
Set<InetAddress> endpoints = AntiEntropyService.getNeighbors(tablename);
if (endpoints.isEmpty())
{
logger.info("No neighbors to repair with: " + getName() + " completed.");
return;
}
// Checking all nodes are live
for (InetAddress endpoint : endpoints)
{
if (!FailureDetector.instance.isAlive(endpoint))
{
logger.info("Could not proceed on repair because a neighbor (" + endpoint + ") is dead: " + getName() + " failed.");
return;
}
}
// begin a repair session
Callback callback = new Callback();
AntiEntropyService.this.sessions.put(getName(), callback);
try
{
// request that all relevant endpoints generate trees
for (String cfname : cfnames)
{
// send requests to remote nodes and record them
for (InetAddress endpoint : endpoints)
requests.put(AntiEntropyService.this.request(getName(), endpoint, tablename, cfname), this);
// send but don't record an outstanding request to the local node
AntiEntropyService.this.request(getName(), FBUtilities.getLocalAddress(), tablename, cfname);
}
logger.info("Waiting for repair requests: " + requests.keySet());
requestsMade.signalAll();
// block whatever thread started this session until all requests have been returned:
// if this thread dies, the session will still complete in the background
callback.completed.await();
}
catch (InterruptedException e)
{
throw new RuntimeException("Interrupted while waiting for repair: repair will continue in the background.");
}
}
/**
* Receives notifications of completed requests, and sets a condition when all requests
* triggered by this session have completed.
*/
class Callback
{
public final SimpleCondition completed = new SimpleCondition();
public void completed(TreeRequest request)
{
// don't mark any requests completed until all requests have been made
try
{
blockUntilRunning();
}
catch (InterruptedException e)
{
throw new AssertionError(e);
}
requests.remove(request);
logger.info("{} completed successfully: {} outstanding.", request, requests.size());
if (!requests.isEmpty())
return;
// all requests completed
logger.info("Repair session " + getName() + " completed successfully.");
AntiEntropyService.this.sessions.remove(getName());
completed.signalAll();
}
}
}
}