“租约” ，何为租约，一个租约管理着一个client的所有锁，对于每个client 都有一个相应的租约，但一个client 定期 check in 时租约的时间戳就会更新，当一个client 停止的时候并且允许租约到期，则对应的所有 锁都会释放。
大家来看看租约这个类：
class Lease implements Comparable<Lease> {
// 租约的持有者，就是客户端名称
private final String holder;
//最后一次检入时间
private long lastUpdate;
//持有的文件路径集
private final Collection<String> paths = new TreeSet<String>();
}
租约管理的超时限制：
- 软超时默认 60000ms=1min 当对一个文件进行创建或者append的时候会判断，配置 ：hdfs.regionserver.lease.period
- 硬超时默认时 60*60000ms=1h ,namenode 会监控硬链接是否超时，若超时会恢复租约
租约恢复算法
- Namenode检索租赁信息
- 对于租约中的每个文件f，使用f的最后一个块b
- 获取包含b的datanode
- 指定其中一个datanode 作为master并命名其为p
- p 从namenode 获取一个新生成的时间戳
- p 从每个datanode 获取块信息
- p 计算最小块的长度 length
- p 使用新生成的时间戳和最小块长度 更新具有有效的生成时间戳的datanode
- p 让namenode 更新信息
- namenode 更新块信息
- Namenode在删除所有文件后从租约中删除f并删除租约
下面的这个方法会在客户端create或者append的时候执行该方法：
private void recoverLeaseInternal(INodeFile fileInode,
String src, String holder, String clientMachine, boolean force)
throws IOException {
assert hasWriteLock();
if (fileInode != null && fileInode.isUnderConstruction()) {
INodeFileUnderConstruction pendingFile = (INodeFileUnderConstruction) fileInode;
/** 如果文件正在构建中，那么它必须在我们的租约中。找到合适的租赁记录。*/
Lease lease = leaseManager.getLease(holder);
//通过文件地址获取租约，若发现原创建该文件，会报异常
if (!force && lease != null) {
Lease leaseFile = leaseManager.getLeaseByPath(src);
if ((leaseFile != null && leaseFile.equals(lease))) {
throw new AlreadyBeingCreatedException(
"failed to create file " + src + " for " + holder +
" on client " + clientMachine +
" because current leaseholder is trying to recreate file.");
}
}
//
// 获取原始的持有者
lease = leaseManager.getLease(pendingFile.getClientName());
if (lease == null) {
throw new AlreadyBeingCreatedException(
"failed to create file " + src + " for " + holder +
" on client " + clientMachine +
" because pendingCreates is non-null but no leases found.");
}
if (force) {
//如果是强制的
// 直接关闭：不需要 等待软超时过期
// 只关闭当前的文件
LOG.info("recoverLease: " + lease + ", src=" + src +
" from client " + pendingFile.getClientName());
internalReleaseLease(lease, src, holder);
} else {
assert lease.getHolder().equals(pendingFile.getClientName()) :
"Current lease holder " + lease.getHolder() +
" does not match file creator " + pendingFile.getClientName();
//如果软超时已经超时 则尝试恢复租约
if (lease.expiredSoftLimit()) {
LOG.info("startFile: recover " + lease + ", src=" + src + " client "
+ pendingFile.getClientName());
boolean isClosed = internalReleaseLease(lease, src, null);
if(!isClosed)
throw new RecoveryInProgressException(
"Failed to close file " + src +
". Lease recovery is in progress. Try again later.");
} else {
final BlockInfo lastBlock = pendingFile.getLastBlock();
if (lastBlock != null
&& lastBlock.getBlockUCState() == BlockUCState.UNDER_RECOVERY) {
throw new RecoveryInProgressException("Recovery in progress, file ["
+ src + "], " + "lease owner [" + lease.getHolder() + "]");
} else {
throw new AlreadyBeingCreatedException("Failed to create file ["
+ src + "] for [" + holder + "] on client [" + clientMachine
+ "], because this file is already being created by ["
+ pendingFile.getClientName() + "] on ["
+ pendingFile.getClientMachine() + "]");
}
}
}
}
}
