org.apache.hadoop.hbase.zookeeper

Class RecoverableZooKeeper

java.lang.Object

org.apache.hadoop.hbase.zookeeper.RecoverableZooKeeper

@InterfaceAudience.Private
public class RecoverableZooKeeper
extends Object

A zookeeper that can handle 'recoverable' errors. To handle recoverable errors, developers need to realize that there are two classes of requests: idempotent and non-idempotent requests. Read requests and unconditional sets and deletes are examples of idempotent requests, they can be reissued with the same results. (Although, the delete may throw a NoNodeException on reissue its effect on the ZooKeeper state is the same.) Non-idempotent requests need special handling, application and library writers need to keep in mind that they may need to encode information in the data or name of znodes to detect retries. A simple example is a create that uses a sequence flag. If a process issues a create("/x-", ..., SEQUENCE) and gets a connection loss exception, that process will reissue another create("/x-", ..., SEQUENCE) and get back x-111. When the process does a getChildren("/"), it sees x-1,x-30,x-109,x-110,x-111, now it could be that x-109 was the result of the previous create, so the process actually owns both x-109 and x-111. An easy way around this is to use "x-process id-" when doing the create. If the process is using an id of 352, before reissuing the create it will do a getChildren("/") and see "x-222-1", "x-542-30", "x-352-109", x-333-110". The process will know that the original create succeeded an the znode it created is "x-352-109".

See Also:

"http://wiki.apache.org/hadoop/ZooKeeper/ErrorHandling"

Constructor Summary

Constructors

Constructor and Description
RecoverableZooKeeper(String quorumServers, int sessionTimeout, Watcher watcher, int maxRetries, int retryIntervalMillis)
RecoverableZooKeeper(String quorumServers, int sessionTimeout, Watcher watcher, int maxRetries, int retryIntervalMillis, String identifier)

Method Summary

Modifier and Type	Method and Description
protected ZooKeeper	checkZk() Try to create a Zookeeper connection.
void	close()
String	create(String path, byte[] data, List<ACL> acl, CreateMode createMode) NONSEQUENTIAL create is idempotent operation.
void	delete(String path, int version) delete is an idempotent operation.
Stat	exists(String path, boolean watch) exists is an idempotent operation.
Stat	exists(String path, Watcher watcher) exists is an idempotent operation.
List<ACL>	getAcl(String path, Stat stat) getAcl is an idempotent operation.
List<String>	getChildren(String path, Watcher watcher) getChildren is an idempotent operation.
byte[]	getData(String path, boolean watch, Stat stat) getData is an idemnpotent operation.
byte[]	getData(String path, Watcher watcher, Stat stat) getData is an idempotent operation.
String	getIdentifier()
long	getSessionId()
byte[]	getSessionPasswd()
States	getState()
ZooKeeper	getZooKeeper()
List<OpResult>	multi(Iterable<Op> ops) Run multiple operations in a transactional manner.
void	reconnectAfterExpiration()
byte[]	removeMetaData(byte[] data)
Stat	setAcl(String path, List<ACL> acls, int version) setAcl is an idempotent operation.
Stat	setData(String path, byte[] data, int version) setData is NOT an idempotent operation.
void	sync(String path, AsyncCallback.VoidCallback cb, Object ctx)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

RecoverableZooKeeper

public RecoverableZooKeeper(String quorumServers,
                            int sessionTimeout,
                            Watcher watcher,
                            int maxRetries,
                            int retryIntervalMillis)
                     throws IOException

Throws:

IOException

RecoverableZooKeeper

public RecoverableZooKeeper(String quorumServers,
                            int sessionTimeout,
                            Watcher watcher,
                            int maxRetries,
                            int retryIntervalMillis,
                            String identifier)
                     throws IOException

Throws:

IOException

Method Detail

checkZk

protected ZooKeeper checkZk()
                     throws KeeperException

Try to create a Zookeeper connection. Turns any exception encountered into a KeeperException.OperationTimeoutException so it can retried.

Returns:

The created Zookeeper connection object

Throws:

KeeperException

reconnectAfterExpiration

public void reconnectAfterExpiration()
                              throws IOException,
                                     KeeperException,
                                     InterruptedException

Throws:

IOException

KeeperException

InterruptedException

delete

public void delete(String path,
                   int version)
            throws InterruptedException,
                   KeeperException

delete is an idempotent operation. Retry before throwing exception. This function will not throw NoNodeException if the path does not exist.

Throws:

InterruptedException

KeeperException

exists

public Stat exists(String path,
                   Watcher watcher)
            throws KeeperException,
                   InterruptedException

exists is an idempotent operation. Retry before throwing exception

Returns:

A Stat instance

Throws:

KeeperException

InterruptedException

exists

public Stat exists(String path,
                   boolean watch)
            throws KeeperException,
                   InterruptedException

exists is an idempotent operation. Retry before throwing exception

Returns:

A Stat instance

Throws:

KeeperException

InterruptedException

getChildren

public List<String> getChildren(String path,
                                Watcher watcher)
                         throws KeeperException,
                                InterruptedException

getChildren is an idempotent operation. Retry before throwing exception

Returns:

List of children znodes

Throws:

KeeperException

InterruptedException

getData

public byte[] getData(String path,
                      Watcher watcher,
                      Stat stat)
               throws KeeperException,
                      InterruptedException

getData is an idempotent operation. Retry before throwing exception

Returns:

Data

Throws:

KeeperException

InterruptedException

getData

public byte[] getData(String path,
                      boolean watch,
                      Stat stat)
               throws KeeperException,
                      InterruptedException

getData is an idemnpotent operation. Retry before throwing exception

Returns:

Data

Throws:

KeeperException

InterruptedException

setData

public Stat setData(String path,
                    byte[] data,
                    int version)
             throws KeeperException,
                    InterruptedException

setData is NOT an idempotent operation. Retry may cause BadVersion Exception Adding an identifier field into the data to check whether badversion is caused by the result of previous correctly setData

Returns:

Stat instance

Throws:

KeeperException

InterruptedException

getAcl

public List<ACL> getAcl(String path,
                        Stat stat)
                 throws KeeperException,
                        InterruptedException

getAcl is an idempotent operation. Retry before throwing exception

Returns:

list of ACLs

Throws:

KeeperException

InterruptedException

setAcl

public Stat setAcl(String path,
                   List<ACL> acls,
                   int version)
            throws KeeperException,
                   InterruptedException

setAcl is an idempotent operation. Retry before throwing exception

Returns:

list of ACLs

Throws:

KeeperException

InterruptedException

create

public String create(String path,
                     byte[] data,
                     List<ACL> acl,
                     CreateMode createMode)
              throws KeeperException,
                     InterruptedException

NONSEQUENTIAL create is idempotent operation. Retry before throwing exceptions. But this function will not throw the NodeExist exception back to the application.

But SEQUENTIAL is NOT idempotent operation. It is necessary to add identifier to the path to verify, whether the previous one is successful or not.

Returns:

Path

Throws:

KeeperException

InterruptedException

multi

public List<OpResult> multi(Iterable<Op> ops)
                     throws KeeperException,
                            InterruptedException

Run multiple operations in a transactional manner. Retry before throwing exception

Throws:

KeeperException

InterruptedException

removeMetaData

public byte[] removeMetaData(byte[] data)

getSessionId

public long getSessionId()

close

public void close()
           throws InterruptedException

Throws:

InterruptedException

getState

public States getState()

getZooKeeper

public ZooKeeper getZooKeeper()

getSessionPasswd

public byte[] getSessionPasswd()

sync

public void sync(String path,
                 AsyncCallback.VoidCallback cb,
                 Object ctx)
          throws KeeperException

Throws:

KeeperException

getIdentifier

public String getIdentifier()