THIS IS A TEST INSTANCE. ALL YOUR CHANGES WILL BE LOST!!!!
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Consider an example of a table "Carshbase-table" has three columns C1, C2, C3. The picture below shows us the history of data written for a particular row (say with row key "foo").
- The user specifies nothing specific to read. In this mode, the latest snapshot of the table will be taken by default. This snapshot would be used to read the table.
Example:
User specification : Read table "Cars".
Output : (Z,Z,P).
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When a job (or user) requests the revision manager to take a latest snapshot, the list of currently running transactions is consulted. The lowest revision number minus 1 , among the list is used in the snapshot.
UML diagram
The following picture shows the class diagram for the zookeeper based revision manager. 
APIs
The APIs provided by the revision manager interface are:
| Code Block |
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/**
* Initialize the revision manager.
*/
public void initialize(Properties properties);
/**
* Opens the revision manager.
*
* @throws IOException
*/
public void open() throws IOException;
/**
* Closes the revision manager.
*
* @throws IOException
*/
public void close() throws IOException;
/**
* Start the write transaction.
*
* @param table The name of table involved in the transaction.
* @param families The column families of table in which data will be written by the transaction.
* @return An instance of Transaction
* @throws IOException
*/
public Transaction beginWriteTransaction(String table, List<String> families)
throws IOException;
/**
* Start the write transaction.
*
* @param table The name of table involved in the transaction.
* @param families The column families of table in which data will be written by the transaction.
* @param keepAlive The duration ( in milliseconds) after which the transaction will expire.
* @return An instance of Transaction
* @throws IOException
*/
public Transaction beginWriteTransaction(String table,
List<String> families, long keepAlive) throws IOException;
/**
* Commit the write transaction.
*
* @param transaction An instance of Transaction to be committed.
* @throws IOException
*/
public void commitWriteTransaction(Transaction transaction)
throws IOException;
/**
* Abort the write transaction.
*
* @param transaction An instance of Transaction to be aborted.
* @throws IOException
*/
public void abortWriteTransaction(Transaction transaction)
throws IOException;
/**
* Create the latest snapshot of the table.
*
* @param tableName The name of the table to create a snapshot.
* @return An instance of TableSnapshot.
* @throws IOException
*/
public TableSnapshot createSnapshot(String tableName) throws IOException;
/**
* Create the snapshot of the table using the revision number.
*
* @param tableName The name of the table to create a snapshot.
* @param revision The revision number to be used.
* @return An instance of TableSnapshot.
* @throws IOException
*/
public TableSnapshot createSnapshot(String tableName, long revision)
throws IOException;
/**
* Extends the expiration of a transaction by the time indicated by keep alive.
*
* @param transaction An instance of Transaction.
* @throws IOException
*/
public void keepAlive(Transaction transaction) throws IOException;
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