Package org.apache.hadoop.hdfs.server.federation.router.security.token

Class DistributedSQLCounter

java.lang.Object

org.apache.hadoop.hdfs.server.federation.router.security.token.DistributedSQLCounter

public class DistributedSQLCounter
extends Object

Distributed counter that relies on a SQL database to synchronize between multiple clients. This expects a table with a single int field to exist in the database. One record must exist on the table at all times, representing the last used value reserved by a client.

Constructor Summary

Constructors

Constructor	Description
DistributedSQLCounter(String field, String table, SQLConnectionFactory connectionFactory)

Method Summary

Modifier and Type	Method	Description
int	incrementCounterValue(int amount)	Increments the counter by the given amount and returns the previous counter value.
int	selectCounterValue()	Obtains the value of the counter.
void	updateCounterValue(int value)	Sets the counter to the given value.
void	updateCounterValue(int value, Connection connection)	Sets the counter to the given value.

Methods inherited from class java.lang.Object

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

Constructor Details

DistributedSQLCounter

public DistributedSQLCounter(String field,
 String table,
 SQLConnectionFactory connectionFactory)

Method Details

selectCounterValue

public int selectCounterValue()
                       throws SQLException

Obtains the value of the counter.

Returns:

counter value.

Throws:

SQLException - if querying the database fails.

updateCounterValue

public void updateCounterValue(int value)
                        throws SQLException

Sets the counter to the given value.

Parameters:

value - Value to assign to counter.

Throws:

SQLException - if querying the database fails.

updateCounterValue

public void updateCounterValue(int value,
 Connection connection)
                        throws SQLException

Sets the counter to the given value.

Parameters:

value - Value to assign to counter.

connection - Connection to database hosting the counter table.

Throws:

SQLException - if querying the database fails.

incrementCounterValue

public int incrementCounterValue(int amount)
                          throws SQLException

Increments the counter by the given amount and returns the previous counter value.

Parameters:

amount - Amount to increase the counter.

Returns:

Previous counter value.

Throws:

SQLException - if querying the database fails.