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"

Field Summary

Fields

Modifier and Type	Field and Description
private byte[]	id
private String	identifier
private static org.slf4j.Logger	LOG
private String	quorumServers
private RetryCounterFactory	retryCounterFactory
private int	sessionTimeout
private org.apache.zookeeper.Watcher	watcher
private org.apache.zookeeper.ZooKeeper	zk

Constructor Summary

Constructors

Constructor and Description
RecoverableZooKeeper(String quorumServers, int sessionTimeout, org.apache.zookeeper.Watcher watcher, int maxRetries, int retryIntervalMillis, int maxSleepTime)
RecoverableZooKeeper(String quorumServers, int sessionTimeout, org.apache.zookeeper.Watcher watcher, int maxRetries, int retryIntervalMillis, int maxSleepTime, String identifier)

Method Summary

Modifier and Type	Method and Description
protected org.apache.zookeeper.ZooKeeper	checkZk() Try to create a ZooKeeper connection.
void	close()
String	create(String path, byte[] data, List<org.apache.zookeeper.data.ACL> acl, org.apache.zookeeper.CreateMode createMode) NONSEQUENTIAL create is idempotent operation.
private String	createNonSequential(String path, byte[] data, List<org.apache.zookeeper.data.ACL> acl, org.apache.zookeeper.CreateMode createMode)
private String	createSequential(String path, byte[] data, List<org.apache.zookeeper.data.ACL> acl, org.apache.zookeeper.CreateMode createMode)
void	delete(String path, int version) delete is an idempotent operation.
org.apache.zookeeper.data.Stat	exists(String path, boolean watch) exists is an idempotent operation.
org.apache.zookeeper.data.Stat	exists(String path, org.apache.zookeeper.Watcher watcher) exists is an idempotent operation.
private static List<String>	filterByPrefix(List<String> nodes, String... prefixes) Filters the given node list by the given prefixes.
private String	findPreviousSequentialNode(String path)
List<org.apache.zookeeper.data.ACL>	getAcl(String path, org.apache.zookeeper.data.Stat stat) getAcl is an idempotent operation.
List<String>	getChildren(String path, boolean watch) getChildren is an idempotent operation.
List<String>	getChildren(String path, org.apache.zookeeper.Watcher watcher) getChildren is an idempotent operation.
byte[]	getData(String path, boolean watch, org.apache.zookeeper.data.Stat stat) getData is an idempotent operation.
byte[]	getData(String path, org.apache.zookeeper.Watcher watcher, org.apache.zookeeper.data.Stat stat) getData is an idempotent operation.
String	getIdentifier()
long	getSessionId()
byte[]	getSessionPasswd()
org.apache.zookeeper.ZooKeeper.States	getState()
org.apache.zookeeper.ZooKeeper	getZooKeeper()
List<org.apache.zookeeper.OpResult>	multi(Iterable<org.apache.zookeeper.Op> ops) Run multiple operations in a transactional manner.
private Iterable<org.apache.zookeeper.Op>	prepareZKMulti(Iterable<org.apache.zookeeper.Op> ops) Convert Iterable of Op we got into the ZooKeeper.Op instances to actually pass to multi (need to do this in order to appendMetaData).
void	reconnectAfterExpiration()
private void	retryOrThrow(RetryCounter retryCounter, org.apache.zookeeper.KeeperException e, String opName)
org.apache.zookeeper.data.Stat	setAcl(String path, List<org.apache.zookeeper.data.ACL> acls, int version) setAcl is an idempotent operation.
org.apache.zookeeper.data.Stat	setData(String path, byte[] data, int version) setData is NOT an idempotent operation.
void	sync(String path, org.apache.zookeeper.AsyncCallback.VoidCallback cb, Object ctx)

Methods inherited from class java.lang.Object

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

Field Detail

LOG

private static final org.slf4j.Logger LOG

zk

private org.apache.zookeeper.ZooKeeper zk

retryCounterFactory

private final RetryCounterFactory retryCounterFactory

identifier

private final String identifier

id

private final byte[] id

watcher

private final org.apache.zookeeper.Watcher watcher

sessionTimeout

private final int sessionTimeout

quorumServers

private final String quorumServers

Constructor Detail

RecoverableZooKeeper

public RecoverableZooKeeper(String quorumServers,
                            int sessionTimeout,
                            org.apache.zookeeper.Watcher watcher,
                            int maxRetries,
                            int retryIntervalMillis,
                            int maxSleepTime)
                     throws IOException

Throws:

IOException

RecoverableZooKeeper

public RecoverableZooKeeper(String quorumServers,
                            int sessionTimeout,
                            org.apache.zookeeper.Watcher watcher,
                            int maxRetries,
                            int retryIntervalMillis,
                            int maxSleepTime,
                            String identifier)
                     throws IOException

Throws:

IOException

Method Detail

checkZk

protected org.apache.zookeeper.ZooKeeper checkZk()
                                          throws org.apache.zookeeper.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:

org.apache.zookeeper.KeeperException - if a ZooKeeper operation fails

reconnectAfterExpiration

public void reconnectAfterExpiration()
                              throws IOException,
                                     org.apache.zookeeper.KeeperException,
                                     InterruptedException

Throws:

IOException

org.apache.zookeeper.KeeperException

InterruptedException

delete

public void delete(String path,
                   int version)
            throws InterruptedException,
                   org.apache.zookeeper.KeeperException

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

Throws:

InterruptedException

org.apache.zookeeper.KeeperException

exists

public org.apache.zookeeper.data.Stat exists(String path,
                                             org.apache.zookeeper.Watcher watcher)
                                      throws org.apache.zookeeper.KeeperException,
                                             InterruptedException

exists is an idempotent operation. Retry before throwing exception

Returns:

A Stat instance

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

exists

public org.apache.zookeeper.data.Stat exists(String path,
                                             boolean watch)
                                      throws org.apache.zookeeper.KeeperException,
                                             InterruptedException

exists is an idempotent operation. Retry before throwing exception

Returns:

A Stat instance

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

retryOrThrow

private void retryOrThrow(RetryCounter retryCounter,
                          org.apache.zookeeper.KeeperException e,
                          String opName)
                   throws org.apache.zookeeper.KeeperException

Throws:

org.apache.zookeeper.KeeperException

getChildren

public List<String> getChildren(String path,
                                org.apache.zookeeper.Watcher watcher)
                         throws org.apache.zookeeper.KeeperException,
                                InterruptedException

getChildren is an idempotent operation. Retry before throwing exception

Returns:

List of children znodes

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

getChildren

public List<String> getChildren(String path,
                                boolean watch)
                         throws org.apache.zookeeper.KeeperException,
                                InterruptedException

getChildren is an idempotent operation. Retry before throwing exception

Returns:

List of children znodes

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

getData

public byte[] getData(String path,
                      org.apache.zookeeper.Watcher watcher,
                      org.apache.zookeeper.data.Stat stat)
               throws org.apache.zookeeper.KeeperException,
                      InterruptedException

getData is an idempotent operation. Retry before throwing exception

Returns:

Data

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

getData

public byte[] getData(String path,
                      boolean watch,
                      org.apache.zookeeper.data.Stat stat)
               throws org.apache.zookeeper.KeeperException,
                      InterruptedException

getData is an idempotent operation. Retry before throwing exception

Returns:

Data

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

setData

public org.apache.zookeeper.data.Stat setData(String path,
                                              byte[] data,
                                              int version)
                                       throws org.apache.zookeeper.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:

org.apache.zookeeper.KeeperException

InterruptedException

getAcl

public List<org.apache.zookeeper.data.ACL> getAcl(String path,
                                                  org.apache.zookeeper.data.Stat stat)
                                           throws org.apache.zookeeper.KeeperException,
                                                  InterruptedException

getAcl is an idempotent operation. Retry before throwing exception

Returns:

list of ACLs

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

setAcl

public org.apache.zookeeper.data.Stat setAcl(String path,
                                             List<org.apache.zookeeper.data.ACL> acls,
                                             int version)
                                      throws org.apache.zookeeper.KeeperException,
                                             InterruptedException

setAcl is an idempotent operation. Retry before throwing exception

Returns:

list of ACLs

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

create

public String create(String path,
                     byte[] data,
                     List<org.apache.zookeeper.data.ACL> acl,
                     org.apache.zookeeper.CreateMode createMode)
              throws org.apache.zookeeper.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:

org.apache.zookeeper.KeeperException

InterruptedException

createNonSequential

private String createNonSequential(String path,
                                   byte[] data,
                                   List<org.apache.zookeeper.data.ACL> acl,
                                   org.apache.zookeeper.CreateMode createMode)
                            throws org.apache.zookeeper.KeeperException,
                                   InterruptedException

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

createSequential

private String createSequential(String path,
                                byte[] data,
                                List<org.apache.zookeeper.data.ACL> acl,
                                org.apache.zookeeper.CreateMode createMode)
                         throws org.apache.zookeeper.KeeperException,
                                InterruptedException

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

prepareZKMulti

private Iterable<org.apache.zookeeper.Op> prepareZKMulti(Iterable<org.apache.zookeeper.Op> ops)
                                                  throws UnsupportedOperationException

Convert Iterable of Op we got into the ZooKeeper.Op instances to actually pass to multi (need to do this in order to appendMetaData).

Throws:

UnsupportedOperationException

multi

public List<org.apache.zookeeper.OpResult> multi(Iterable<org.apache.zookeeper.Op> ops)
                                          throws org.apache.zookeeper.KeeperException,
                                                 InterruptedException

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

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

findPreviousSequentialNode

private String findPreviousSequentialNode(String path)
                                   throws org.apache.zookeeper.KeeperException,
                                          InterruptedException

Throws:

org.apache.zookeeper.KeeperException

InterruptedException

getSessionId

public long getSessionId()

close

public void close()
           throws InterruptedException

Throws:

InterruptedException

getState

public org.apache.zookeeper.ZooKeeper.States getState()

getZooKeeper

public org.apache.zookeeper.ZooKeeper getZooKeeper()

getSessionPasswd

public byte[] getSessionPasswd()

sync

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

Throws:

org.apache.zookeeper.KeeperException

filterByPrefix

private static List<String> filterByPrefix(List<String> nodes,
                                           String... prefixes)

Filters the given node list by the given prefixes. This method is all-inclusive--if any element in the node list starts with any of the given prefixes, then it is included in the result.

Parameters:

nodes - the nodes to filter

prefixes - the prefixes to include in the result

Returns:

list of every element that starts with one of the prefixes

getIdentifier

public String getIdentifier()