zookeeper集群模式（三）zookeeper数据库ZKDataBase的加载
- QuorumPeer之重写继承自Thread之后的start()方法
@Override
public synchronized void start() {
if (!getView().containsKey(myid)) {
throw new RuntimeException("My id " + myid + " not in the peer list");
}
loadDataBase();
startServerCnxnFactory();
try {
adminServer.start();
} catch (AdminServerException e) {
LOG.warn("Problem starting AdminServer", e);
System.out.println(e);
}
startLeaderElection();
startJvmPauseMonitor();
super.start();
}
它做了以下几件事：
1.判断投票验证器中是否包含当前服务器serverId，不存在直接终止启动
2.加载ZKDatabase，就是加载快照文件以及事务日志文件
3.启动selector线程、accept线程、WorkerService以及连接超时验证线程
4.启动AdminServer
5.为开启Leader选举做好准备工作
6.启动检测JVM运行情况线程
7.启动QuorumPeer本身的线程，即循环进行检测是否LOOKING状态来判断是否需要启动Leader选举流程
ZKDataBase的数据恢复流程：loadDataBase()
private void loadDataBase() {
try {
zkDb.loadDataBase();
// load the epochs
long lastProcessedZxid = zkDb.getDataTree().lastProcessedZxid;
long epochOfZxid = ZxidUtils.getEpochFromZxid(lastProcessedZxid);
try {
currentEpoch = readLongFromFile(CURRENT_EPOCH_FILENAME);
} catch(FileNotFoundException e) {
// pick a reasonable epoch number
// this should only happen once when moving to a
// new code version
currentEpoch = epochOfZxid;
LOG.info(CURRENT_EPOCH_FILENAME
+ " not found! Creating with a reasonable default of {}. This should only happen when you are upgrading your installation",
currentEpoch);
writeLongToFile(CURRENT_EPOCH_FILENAME, currentEpoch);
}
if (epochOfZxid > currentEpoch) {
throw new IOException("The current epoch, " + ZxidUtils.zxidToString(currentEpoch) + ", is older than the last zxid, " + lastProcessedZxid);
}
try {
acceptedEpoch = readLongFromFile(ACCEPTED_EPOCH_FILENAME);
} catch(FileNotFoundException e) {
// pick a reasonable epoch number
// this should only happen once when moving to a
// new code version
acceptedEpoch = epochOfZxid;
LOG.info(ACCEPTED_EPOCH_FILENAME
+ " not found! Creating with a reasonable default of {}. This should only happen when you are upgrading your installation",
acceptedEpoch);
writeLongToFile(ACCEPTED_EPOCH_FILENAME, acceptedEpoch);
}
if (acceptedEpoch < currentEpoch) {
throw new IOException("The accepted epoch, " + ZxidUtils.zxidToString(acceptedEpoch) + " is less than the current epoch, " + ZxidUtils.zxidToString(currentEpoch));
}
} catch(IOException ie) {
LOG.error("Unable to load database on disk", ie);
throw new RuntimeException("Unable to run quorum server ", ie);
}
}
这个方法主要做了以下几件事：
1.加载数据库
2.获取currentEpoch、acceptedEpoch，并判断其是否合法
- ZKDatabase之loadDataBase()
public long loadDataBase() throws IOException {
long startTime = Time.currentElapsedTime();
long zxid = snapLog.restore(dataTree, sessionsWithTimeouts, commitProposalPlaybackListener);
initialized = true;
long loadTime = Time.currentElapsedTime() - startTime;
ServerMetrics.getMetrics().DB_INIT_TIME.add(loadTime);
LOG.info("Snapshot loaded in " + loadTime + " ms");
return zxid;
}
这个做了一下数据库恢复的时间统计，具体的恢复逻辑在FileTxnSnapLog的restore(DataTree dt, Map
- restore(DataTree dt, Map
public long restore(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
long snapLoadingStartTime = Time.currentElapsedTime();
long deserializeResult = snapLog.deserialize(dt, sessions);
ServerMetrics.getMetrics().STARTUP_SNAP_LOAD_TIME.add(
Time.currentElapsedTime() - snapLoadingStartTime);
FileTxnLog txnLog = new FileTxnLog(dataDir);
boolean trustEmptyDB;
File initFile = new File(dataDir.getParent(), "initialize");
if (Files.deleteIfExists(initFile.toPath())) {
LOG.info("Initialize file found, an empty database will not block voting participation");
trustEmptyDB = true;
} else {
trustEmptyDB = autoCreateDB;
}
if (-1L == deserializeResult) {
/* this means that we couldn't find any snapshot, so we need to
* initialize an empty database (reported in ZOOKEEPER-2325) */
if (txnLog.getLastLoggedZxid() != -1) {
throw new IOException(
"No snapshot found, but there are log entries. " +
"Something is broken!");
}
if (trustEmptyDB) {
/* TODO: (br33d) we should either put a ConcurrentHashMap on restore()
* or use Map on save() */
save(dt, (ConcurrentHashMap<Long, Integer>)sessions, false);
/* return a zxid of 0, since we know the database is empty */
return 0L;
} else {
/* return a zxid of -1, since we are possibly missing data */
LOG.warn("Unexpected empty data tree, setting zxid to -1");
dt.lastProcessedZxid = -1L;
return -1L;
}
}
return fastForwardFromEdits(dt, sessions, listener);
}
这个方法做了以下几件事：
1.将快照文件的数据刷到DataTree以及会话信息刷到sessions
2.耗时信息统计
3.判断是否存在快照文件以及是否需要初始化一个空的数据库
4.通过事务日志恢复最新的数据
从快照文件中恢复数据的实现：snapLog.deserialize(dt, sessions)
public long deserialize(DataTree dt, Map<Long, Integer> sessions)
throws IOException {
// we run through 100 snapshots (not all of them)
// if we cannot get it running within 100 snapshots
// we should give up
List<File> snapList = findNValidSnapshots(100);
if (snapList.size() == 0) {
return -1L;
}
File snap = null;
boolean foundValid = false;
for (int i = 0, snapListSize = snapList.size(); i < snapListSize; i++) {
snap = snapList.get(i);
LOG.info("Reading snapshot " + snap);
try (CheckedInputStream snapIS = SnapStream.getInputStream(snap)) {
InputArchive ia = BinaryInputArchive.getArchive(snapIS);
deserialize(dt, sessions, ia);
SnapStream.checkSealIntegrity(snapIS, ia);
foundValid = true;
break;
} catch (IOException e) {
LOG.warn("problem reading snap file " + snap, e);
}
}
if (!foundValid) {
throw new IOException("Not able to find valid snapshots in " + snapDir);
}
dt.lastProcessedZxid = Util.getZxidFromName(snap.getName(), SNAPSHOT_FILE_PREFIX);
lastSnapshotInfo = new SnapshotInfo(dt.lastProcessedZxid, snap.lastModified() / 1000);
return dt.lastProcessedZxid;
}
这个方法有以下几个步骤：
1.寻找最多不超过100个的合法快照文件
2.如果存在快照文件的话，依次遍历并尝试解析
3.如果解析成功，缓存这次的解析结果并返回解析出来的最后处理的事务id
接下来看看解析的过程
public void deserialize(DataTree dt, Map<Long, Integer> sessions,
InputArchive ia) throws IOException {
FileHeader header = new FileHeader();
header.deserialize(ia, "fileheader");
if (header.getMagic() != SNAP_MAGIC) {
throw new IOException("mismatching magic headers "
+ header.getMagic() +
" != " + FileSnap.SNAP_MAGIC);
}
SerializeUtils.deserializeSnapshot(dt,ia,sessions);
}
- SerializeUtils.deserializeSnapshot(dt,ia,sessions)的实现
public static void deserializeSnapshot(DataTree dt,InputArchive ia,
Map<Long, Integer> sessions) throws IOException {
int count = ia.readInt("count");
while (count > 0) {
long id = ia.readLong("id");
int to = ia.readInt("timeout");
sessions.put(id, to);
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG, ZooTrace.SESSION_TRACE_MASK,
"loadData --- session in archive: " + id
+ " with timeout: " + to);
}
count--;
}
dt.deserialize(ia, "tree");
}
- DataTree类中deserialize(ia, “tree”)的实现
public void deserialize(InputArchive ia, String tag) throws IOException {
aclCache.deserialize(ia);
nodes.clear();
pTrie.clear();
nodeDataSize.set(0);
String path = ia.readString("path");
while (!"/".equals(path)) {
DataNode node = new DataNode();
ia.readRecord(node, "node");
nodes.put(path, node);
synchronized (node) {
aclCache.addUsage(node.acl);
}
int lastSlash = path.lastIndexOf('/');
if (lastSlash == -1) {
root = node;
} else {
String parentPath = path.substring(0, lastSlash);
DataNode parent = nodes.get(parentPath);
if (parent == null) {
throw new IOException("Invalid Datatree, unable to find " +
"parent " + parentPath + " of path " + path);
}
parent.addChild(path.substring(lastSlash + 1));
long eowner = node.stat.getEphemeralOwner();
EphemeralType ephemeralType = EphemeralType.get(eowner);
if (ephemeralType == EphemeralType.CONTAINER) {
containers.add(path);
} else if (ephemeralType == EphemeralType.TTL) {
ttls.add(path);
} else if (eowner != 0) {
HashSet<String> list = ephemerals.get(eowner);
if (list == null) {
list = new HashSet<String>();
ephemerals.put(eowner, list);
}
list.add(path);
}
}
path = ia.readString("path");
}
nodes.put("/", root);
nodeDataSize.set(approximateDataSize());
// we are done with deserializing the
// the datatree
// update the quotas - create path trie
// and also update the stat nodes
setupQuota();
aclCache.purgeUnused();
}
现在解释一下上面几段源码代表的含义：
1.反序列化fileheader并判断魔数
2.在流中读出会话id以及超时时间，并放入sessions map中
3.通过流反序列化出DataTree
4.设置路径trie并设置配额节点的统计信息，以及清除无用的ACL信息
从事务日志中恢复数据的实现：fastForwardFromEdits(dt, sessions, listener)
public long fastForwardFromEdits(DataTree dt, Map<Long, Integer> sessions,
PlayBackListener listener) throws IOException {
TxnIterator itr = txnLog.read(dt.lastProcessedZxid+1);
long highestZxid = dt.lastProcessedZxid;
TxnHeader hdr;
int txnLoaded = 0;
long startTime = Time.currentElapsedTime();
try {
while (true) {
// iterator points to
// the first valid txn when initialized
hdr = itr.getHeader();
if (hdr == null) {
//empty logs
return dt.lastProcessedZxid;
}
if (hdr.getZxid() < highestZxid && highestZxid != 0) {
LOG.error("{}(highestZxid) > {}(next log) for type {}",
highestZxid, hdr.getZxid(), hdr.getType());
} else {
highestZxid = hdr.getZxid();
}
try {
processTransaction(hdr,dt,sessions, itr.getTxn());
txnLoaded++;
} catch(KeeperException.NoNodeException e) {
throw new IOException("Failed to process transaction type: " +
hdr.getType() + " error: " + e.getMessage(), e);
}
listener.onTxnLoaded(hdr, itr.getTxn());
if (!itr.next())
break;
}
} finally {
if (itr != null) {
itr.close();
}
}
long loadTime = Time.currentElapsedTime() - startTime;
LOG.info("{} txns loaded in {} ms", txnLoaded, loadTime);
ServerMetrics.getMetrics().STARTUP_TXNS_LOADED.add(txnLoaded);
ServerMetrics.getMetrics().STARTUP_TXNS_LOAD_TIME.add(loadTime);
return highestZxid;
}
这个方法做了以下几件事：
1.获取之前反序列化出的DataTree的lastProcessedZxid，从事务日志中获取最后一个小于lastProcessedZxid的日志文件和大于lastProcessedZxid的所有日志文件，并且转换成TxnIterator
2.建立循环，判断事务头TxnHeader是否存在以及对比zxid，如果比lastProcessedZxid，那么将它赋值给highestZxid
3.处理事务体，恢复DataTree以及sessions map
4.触发回调，将恢复的事务数据转换成提案Proposal并存入已提交的队列中，等待稍后的数据同步流程将其同步到Follow服务器以及Observer服务器
5.统计恢复的事务数量以及耗时，并返回highestZxid以作为此次数据库恢复之后的最大zxid
- 处理事务体的实现：processTransaction(hdr,dt,sessions, itr.getTxn())
public void processTransaction(TxnHeader hdr,DataTree dt,
Map<Long, Integer> sessions, Record txn)
throws KeeperException.NoNodeException {
ProcessTxnResult rc;
switch (hdr.getType()) {
case OpCode.createSession:
sessions.put(hdr.getClientId(),
((CreateSessionTxn) txn).getTimeOut());
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG,ZooTrace.SESSION_TRACE_MASK,
"playLog --- create session in log: 0x"
+ Long.toHexString(hdr.getClientId())
+ " with timeout: "
+ ((CreateSessionTxn) txn).getTimeOut());
}
// give dataTree a chance to sync its lastProcessedZxid
rc = dt.processTxn(hdr, txn);
break;
case OpCode.closeSession:
sessions.remove(hdr.getClientId());
if (LOG.isTraceEnabled()) {
ZooTrace.logTraceMessage(LOG,ZooTrace.SESSION_TRACE_MASK,
"playLog --- close session in log: 0x"
+ Long.toHexString(hdr.getClientId()));
}
rc = dt.processTxn(hdr, txn);
break;
default:
rc = dt.processTxn(hdr, txn);
}
/**
* Snapshots are lazily created. So when a snapshot is in progress,
* there is a chance for later transactions to make into the
* snapshot. Then when the snapshot is restored, NONODE/NODEEXISTS
* errors could occur. It should be safe to ignore these.
*/
if (rc.err != Code.OK.intValue()) {
LOG.debug(
"Ignoring processTxn failure hdr: {}, error: {}, path: {}",
hdr.getType(), rc.err, rc.path);
}
}
主要步骤如下：
1.判断事务头，如果事务类型是createSession或者closeSession那么相应的在sessions map中添加或者移除数据
2.恢复数据至DataTree
- DataTree中恢复数据的实现：processTxn(TxnHeader header, Record txn)
public ProcessTxnResult processTxn(TxnHeader header, Record txn) {
return this.processTxn(header, txn, false);
}
public ProcessTxnResult processTxn(TxnHeader header, Record txn, boolean isSubTxn)
{
ProcessTxnResult rc = new ProcessTxnResult();
try {
rc.clientId = header.getClientId();
rc.cxid = header.getCxid();
rc.zxid = header.getZxid();
rc.type = header.getType();
rc.err = 0;
rc.multiResult = null;
switch (header.getType()) {
case OpCode.create:
CreateTxn createTxn = (CreateTxn) txn;
rc.path = createTxn.getPath();
createNode(
createTxn.getPath(),
createTxn.getData(),
createTxn.getAcl(),
createTxn.getEphemeral() ? header.getClientId() : 0,
createTxn.getParentCVersion(),
header.getZxid(), header.getTime(), null);
break;
case OpCode.create2:
CreateTxn create2Txn = (CreateTxn) txn;
rc.path = create2Txn.getPath();
Stat stat = new Stat();
createNode(
create2Txn.getPath(),
create2Txn.getData(),
create2Txn.getAcl(),
create2Txn.getEphemeral() ? header.getClientId() : 0,
create2Txn.getParentCVersion(),
header.getZxid(), header.getTime(), stat);
rc.stat = stat;
break;
case OpCode.createTTL:
CreateTTLTxn createTtlTxn = (CreateTTLTxn) txn;
rc.path = createTtlTxn.getPath();
stat = new Stat();
createNode(
createTtlTxn.getPath(),
createTtlTxn.getData(),
createTtlTxn.getAcl(),
EphemeralType.TTL.toEphemeralOwner(createTtlTxn.getTtl()),
createTtlTxn.getParentCVersion(),
header.getZxid(), header.getTime(), stat);
rc.stat = stat;
break;
case OpCode.createContainer:
CreateContainerTxn createContainerTxn = (CreateContainerTxn) txn;
rc.path = createContainerTxn.getPath();
stat = new Stat();
createNode(
createContainerTxn.getPath(),
createContainerTxn.getData(),
createContainerTxn.getAcl(),
EphemeralType.CONTAINER_EPHEMERAL_OWNER,
createContainerTxn.getParentCVersion(),
header.getZxid(), header.getTime(), stat);
rc.stat = stat;
break;
case OpCode.delete:
case OpCode.deleteContainer:
DeleteTxn deleteTxn = (DeleteTxn) txn;
rc.path = deleteTxn.getPath();
deleteNode(deleteTxn.getPath(), header.getZxid());
break;
case OpCode.reconfig:
case OpCode.setData:
SetDataTxn setDataTxn = (SetDataTxn) txn;
rc.path = setDataTxn.getPath();
rc.stat = setData(setDataTxn.getPath(), setDataTxn
.getData(), setDataTxn.getVersion(), header
.getZxid(), header.getTime());
break;
case OpCode.setACL:
SetACLTxn setACLTxn = (SetACLTxn) txn;
rc.path = setACLTxn.getPath();
rc.stat = setACL(setACLTxn.getPath(), setACLTxn.getAcl(),
setACLTxn.getVersion());
break;
case OpCode.closeSession:
killSession(header.getClientId(), header.getZxid());
break;
case OpCode.error:
ErrorTxn errTxn = (ErrorTxn) txn;
rc.err = errTxn.getErr();
break;
case OpCode.check:
CheckVersionTxn checkTxn = (CheckVersionTxn) txn;
rc.path = checkTxn.getPath();
break;
case OpCode.multi:
MultiTxn multiTxn = (MultiTxn) txn ;
List<Txn> txns = multiTxn.getTxns();
rc.multiResult = new ArrayList<ProcessTxnResult>();
boolean failed = false;
for (Txn subtxn : txns) {
if (subtxn.getType() == OpCode.error) {
failed = true;
break;
}
}
boolean post_failed = false;
for (Txn subtxn : txns) {
ByteBuffer bb = ByteBuffer.wrap(subtxn.getData());
Record record = null;
switch (subtxn.getType()) {
case OpCode.create:
record = new CreateTxn();
break;
case OpCode.createTTL:
record = new CreateTTLTxn();
break;
case OpCode.createContainer:
record = new CreateContainerTxn();
break;
case OpCode.delete:
case OpCode.deleteContainer:
record = new DeleteTxn();
break;
case OpCode.setData:
record = new SetDataTxn();
break;
case OpCode.error:
record = new ErrorTxn();
post_failed = true;
break;
case OpCode.check:
record = new CheckVersionTxn();
break;
default:
throw new IOException("Invalid type of op: " + subtxn.getType());
}
assert(record != null);
ByteBufferInputStream.byteBuffer2Record(bb, record);
if (failed && subtxn.getType() != OpCode.error){
int ec = post_failed ? Code.RUNTIMEINCONSISTENCY.intValue()
: Code.OK.intValue();
subtxn.setType(OpCode.error);
record = new ErrorTxn(ec);
}
if (failed) {
assert(subtxn.getType() == OpCode.error) ;
}
TxnHeader subHdr = new TxnHeader(header.getClientId(), header.getCxid(),
header.getZxid(), header.getTime(),
subtxn.getType());
ProcessTxnResult subRc = processTxn(subHdr, record, true);
rc.multiResult.add(subRc);
if (subRc.err != 0 && rc.err == 0) {
rc.err = subRc.err ;
}
}
break;
}
} catch (KeeperException e) {
if (LOG.isDebugEnabled()) {
LOG.debug("Failed: " + header + ":" + txn, e);
}
rc.err = e.code().intValue();
} catch (IOException e) {
if (LOG.isDebugEnabled()) {
LOG.debug("Failed: " + header + ":" + txn, e);
}
}
/*
* Things we can only update after the whole txn is applied to data
* tree.
*
* If we update the lastProcessedZxid with the first sub txn in multi
* and there is a snapshot in progress, it's possible that the zxid
* associated with the snapshot only include partial of the multi op.
*
* When loading snapshot, it will only load the txns after the zxid
* associated with snapshot file, which could cause data inconsistency
* due to missing sub txns.
*
* To avoid this, we only update the lastProcessedZxid when the whole
* multi-op txn is applied to DataTree.
*/
if (!isSubTxn) {
/*
* A snapshot might be in progress while we are modifying the data
* tree. If we set lastProcessedZxid prior to making corresponding
* change to the tree, then the zxid associated with the snapshot
* file will be ahead of its contents. Thus, while restoring from
* the snapshot, the restore method will not apply the transaction
* for zxid associated with the snapshot file, since the restore
* method assumes that transaction to be present in the snapshot.
*
* To avoid this, we first apply the transaction and then modify
* lastProcessedZxid. During restore, we correctly handle the
* case where the snapshot contains data ahead of the zxid associated
* with the file.
*/
if (rc.zxid > lastProcessedZxid) {
lastProcessedZxid = rc.zxid;
}
}
/*
* Snapshots are taken lazily. It can happen that the child
* znodes of a parent are created after the parent
* is serialized. Therefore, while replaying logs during restore, a
* create might fail because the node was already
* created.
*
* After seeing this failure, we should increment
* the cversion of the parent znode since the parent was serialized
* before its children.
*
* Note, such failures on DT should be seen only during
* restore.
*/
if (header.getType() == OpCode.create &&
rc.err == Code.NODEEXISTS.intValue()) {
LOG.debug("Adjusting parent cversion for Txn: " + header.getType() +
" path:" + rc.path + " err: " + rc.err);
int lastSlash = rc.path.lastIndexOf('/');
String parentName = rc.path.substring(0, lastSlash);
CreateTxn cTxn = (CreateTxn)txn;
try {
setCversionPzxid(parentName, cTxn.getParentCVersion(),
header.getZxid());
} catch (KeeperException.NoNodeException e) {
LOG.error("Failed to set parent cversion for: " +
parentName, e);
rc.err = e.code().intValue();
}
} else if (rc.err != Code.OK.intValue()) {
LOG.debug("Ignoring processTxn failure hdr: " + header.getType() +
" : error: " + rc.err);
}
return rc;
}
主要步骤如下：
1.组装事务结果ProcessTxnResult
2.根据事务操作类型对DataTree的node节点进行相应的操作
3.判断是否是子事务，如果不是，对比这次事务的zxid跟lastProcessedZxid以确定是否需要更新lastProcessedZxid
4.如果操作类型是create但是出现NODEEXISTS错误时，需要增加父znode的cversion