apache
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zookeeper
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<h1>BookKeeper Getting Started Guide</h1>
<div id="minitoc-area">
<ul class="minitoc">
<li>
<a href="#bk_GettingStarted">Programming with BookKeeper</a>
<ul class="minitoc">
<li>
<a href="#bk_instance"> Instantiating BookKeeper.</a>
</li>
<li>
<a href="#bk_createLedger"> Creating a ledger. </a>
</li>
<li>
<a href="#bk_writeLedger"> Adding entries to a ledger. </a>
</li>
<li>
<a href="#bk_closeLedger"> Closing a ledger. </a>
</li>
<li>
<a href="#bk_openLedger"> Opening a ledger. </a>
</li>
<li>
<a href="#bk_readLedger"> Reading from ledger </a>
</li>
</ul>
</li>
</ul>
</div>
  

  
  
<a name="N10009"></a><a name="bk_GettingStarted"></a>
<h2 class="h3">Programming with BookKeeper</h2>
<div class="section">
<ul>
      
<li>
        
<p>
<a href="#bk_instance"> Instantiating BookKeeper.</a>
</p>
      
</li>

      
<li>
        
<p>
<a href="#bk_createLedger"> Creating a ledger. </a>
</p>
      
</li>

      
<li>
        
<p>
<a href="#bk_writeLedger"> Adding entries to a ledger. </a>
</p>
      
</li>

      
<li>
        
<p>
<a href="#bk_closeLedger"> Closing a ledger. </a>
</p>
      
</li>
      
	  
<li>
        
<p>
<a href="#bk_openLedger"> Opening a ledger. </a>
</p>
      
</li>
      
      
<li>
        
<p>
<a href="#bk_readLedger"> Reading from ledger </a>
</p>
      
</li>
      
    
</ul>
<a name="N10042"></a><a name="bk_instance"></a>
<h3 class="h4"> Instantiating BookKeeper.</h3>
<p>
    The first step to use BookKeeper is to instantiate a BookKeeper object:
    </p>
<p>
    
<span class="codefrag computeroutput">
    org.apache.bookkeeper.BookKeeper
    </span>
    
</p>
<p>
    There is one BookKeeper constructor:
    </p>
<p>
    
<span class="codefrag computeroutput">
	public BookKeeper(String servers) 
    	throws KeeperException, IOException    
    </span>
   	
</p>
<p> 
    where <span class="codefrag computeroutput">servers</span> is a comma-separated list of ZooKeeper servers.
    </p>
<a name="N10064"></a><a name="bk_createLedger"></a>
<h3 class="h4"> Creating a ledger. </h3>
<p> Before writing entries to BookKeeper, it is necessary to create a ledger. 
    With the current BookKeeper API, it is possible to create a ledger both synchronously
    or asynchronously. The following methods belong
    to <span class="codefrag computeroutput">org.apache.bookkeeper.client.BookKeeper</span>.
    </p>
<p>
   	
<strong>Synchronous call:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
    public LedgerHandle createLedger(int ensSize, int qSize, QMode mode,  byte passwd[])
        throws KeeperException, InterruptedException, 
        IOException, BKException
    </span>
	
</p>
<p>
    where:
    </p>
<ul>
    	
<li>
    	
<p> 
    	
<span class="codefrag computeroutput">ensSize</span> is the number of bookies (ensemble size);
    	</p>
    	
</li>
    
    	
<li> 
    	
<p>
    	
<span class="codefrag computeroutput">qSize</span> is the write quorum size;
    	</p>
    	
</li>
    
    	
<li> 
    	
<p>
    	
<span class="codefrag computeroutput">mode</span> is the ledger mode (QMode.GENERIC, QMode.VERIFIABLE).
    	If <span class="codefrag computeroutput">mode</span> is QMode.GENERIC, then <span class="codefrag computeroutput">ensSize</span> has to
    	be at least <em>3t+1</em>, and <span class="codefrag computeroutput">qSize</span> has to be <em>2t+1</em>.
    	<em>t</em> is the maximum number of tolerated bookie failures.  
    	</p>
    	
</li>
    	
    	
<li>
    	
<p>
    	
<span class="codefrag computeroutput">passwd</span> is a password that authorizes the client to write to the
    	ledger being created.
    	</p>
    	
</li>
    
</ul>
<p>
    All further operations on a ledger are invoked through the <span class="codefrag computeroutput">LedgerHandle</span>
    object returned.
    </p>
<p>
    As a convenience, we provide a <span class="codefrag computeroutput">createLedger</span> with default parameters (3,2,VERIFIABLE), 
    and the only input parameter it requires is a password.
    </p>
<p>
   	
<strong>Asynchronous call:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
    public void asyncCreateLedger(int ensSize, 
            int qSize, 
            QMode mode,  
            byte passwd[],
            CreateCallback cb,
            Object ctx
            )
    throws KeeperException, InterruptedException, 
    IOException, BKException
    </span>
	
</p>
<p>
	The parameters are the same of the synchronous version, with the
	exception of <span class="codefrag computeroutput">cb</span> and <span class="codefrag computeroutput">ctx</span>. <span class="codefrag computeroutput">CreateCallback</span>
	is an interface in <span class="codefrag computeroutput">org.apache.bookkeeper.client.AsyncCallback</span>, and
	a class implementing it has to implement a method called <span class="codefrag computeroutput">createComplete</span>
	that has the following signature: 
    </p>
<p>
	
<span class="codefrag computeroutput">
	void createComplete(int rc, LedgerHandle lh, Object ctx);
	</span>    
	
</p>
<p>
	where:
	</p>
<ul>
		
<li>
		
<p>
		
<span class="codefrag computeroutput">rc</span> is a return code (please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
		</p>
		
</li>
	
		
<li>
		
<p>
		
<span class="codefrag computeroutput">lh</span> is a <span class="codefrag computeroutput">LedgerHandle</span> object to manipulate a ledger;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">ctx</span> is a control object for accountability purposes;
		</p>
		
</li>
	
</ul>
<p>
	The <span class="codefrag computeroutput">ctx</span> object passed as a parameter to the call to create a ledger
	is the one same returned in the callback.
    </p>
<a name="N1012E"></a><a name="bk_writeLedger"></a>
<h3 class="h4"> Adding entries to a ledger. </h3>
<p>
    Once we have a ledger handle <span class="codefrag computeroutput">lh</span> obtained through a call to create a ledger, we
    can start writing entries. As with creating ledgers, we can write both synchronously and 
    asynchronously. The following methods belong
    to <span class="codefrag computeroutput">org.apache.bookkeeper.client.LedgerHandle</span>.
    </p>
<p>
   	
<strong>Synchronous call:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public long addEntry(byte[] data)
    	throws InterruptedException
    </span>
	
</p>
<p>
    where:
    </p>
<ul>
    	
<li>
    	
<p> 
    	
<span class="codefrag computeroutput">data</span> is a byte array;
    	</p>
    	
</li>
    
</ul>
<p>
	A call to <span class="codefrag computeroutput">addEntry</span> returns the status of the operation ((please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
    </p>
<p>
   	
<strong>Asynchronous call:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public void asyncAddEntry(byte[] data, AddCallback cb, Object ctx)
    throws InterruptedException
    </span>
	
</p>
<p>
    It also takes a byte array as the sequence of bytes to be stored as an entry. Additionaly, it takes
    a callback object <span class="codefrag computeroutput">cb</span> and a control object <span class="codefrag computeroutput">ctx</span>. The callback object must implement
    the <span class="codefrag computeroutput">AddCallback</span> interface in <span class="codefrag computeroutput">org.apache.bookkeeper.client.AsyncCallback</span>, and
	a class implementing it has to implement a method called <span class="codefrag computeroutput">addComplete</span>
	that has the following signature: 
    </p>
<p>
	
<span class="codefrag computeroutput">
	void addComplete(int rc, LedgerHandle lh, long entryId, Object ctx);
	</span>    
	
</p>
<p>
	where:
	</p>
<ul>
		
<li>
		
<p>
		
<span class="codefrag computeroutput">rc</span> is a return code (please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
		</p>
		
</li>
	
		
<li>
		
<p>
		
<span class="codefrag computeroutput">lh</span> is a <span class="codefrag computeroutput">LedgerHandle</span> object to manipulate a ledger;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">entryId</span> is the identifier of entry associated with this request;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">ctx</span> is control object used for accountability purposes. 
		</p>
		
</li>
	
</ul>
<a name="N101C9"></a><a name="bk_closeLedger"></a>
<h3 class="h4"> Closing a ledger. </h3>
<p>
    Once a client is done writing, it closes the ledger. The following methods belong
    to <span class="codefrag computeroutput">org.apache.bookkeeper.client.LedgerHandle</span>.
    </p>
<p>
   	
<strong>Synchronous close:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public void close() 
    throws KeeperException, InterruptedException
    </span>
	
</p>
<p>
    It takes no input parameters.
    </p>
<p>
   	
<strong>Asynchronous close:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public void asyncClose(CloseCallback cb, Object ctx)
    throws InterruptedException
    </span>
	
</p>
<p>
    It takes a callback object <span class="codefrag computeroutput">cb</span> and a control object <span class="codefrag computeroutput">ctx</span>. The callback object must implement
    the <span class="codefrag computeroutput">CloseCallback</span> interface in <span class="codefrag computeroutput">org.apache.bookkeeper.client.AsyncCallback</span>, and
	a class implementing it has to implement a method called <span class="codefrag computeroutput">closeComplete</span>
	that has the following signature: 
    </p>
<p>
	
<span class="codefrag computeroutput">
	void closeComplete(int rc, LedgerHandle lh, Object ctx)
	</span>    
	
</p>
<p>
	where:
	</p>
<ul>
		
<li>
		
<p>
		
<span class="codefrag computeroutput">rc</span> is a return code (please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
		</p>
		
</li>
	
		
<li>
		
<p>
		
<span class="codefrag computeroutput">lh</span> is a <span class="codefrag computeroutput">LedgerHandle</span> object to manipulate a ledger;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">ctx</span> is control object used for accountability purposes. 
		</p>
		
</li>
	
</ul>
<a name="N1023E"></a><a name="bk_openLedger"></a>
<h3 class="h4"> Opening a ledger. </h3>
<p>
    To read from a ledger, a client must open it first. The following methods belong
    to <span class="codefrag computeroutput">org.apache.bookkeeper.client.BookKeeper</span>.
    </p>
<p>
   	
<strong>Synchronous open:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public LedgerHandle openLedger(long lId, byte passwd[])
    throws KeeperException, InterruptedException, IOException, BKException
    </span>
	
</p>
<ul>
	
<li>
	
<p>
	
<span class="codefrag computeroutput">ledgerId</span> is the ledger identifier;
	</p>
	
</li>
	
	
<li>
	
<p>
	
<span class="codefrag computeroutput">passwd</span> is a password to access the ledger (used only in the case of <span class="codefrag computeroutput">VERIFIABLE</span> ledgers);
	</p>
	
</li>
	
</ul>
<p>
   	
<strong>Asynchronous open:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public void asyncOpenLedger(long lId, byte passwd[], OpenCallback cb, Object ctx)
    throws InterruptedException
    </span>
	
</p>
<p>
    It also takes a a ledger identifier and a password. Additionaly, it takes a callback object 
    <span class="codefrag computeroutput">cb</span> and a control object <span class="codefrag computeroutput">ctx</span>. The callback object must implement
    the <span class="codefrag computeroutput">OpenCallback</span> interface in <span class="codefrag computeroutput">org.apache.bookkeeper.client.AsyncCallback</span>, and
	a class implementing it has to implement a method called <span class="codefrag computeroutput">openComplete</span>
	that has the following signature: 
    </p>
<p>
	
<span class="codefrag computeroutput">
	public void openComplete(int rc, LedgerHandle lh, Object ctx)
	</span>    
	
</p>
<p>
	where:
	</p>
<ul>
		
<li>
		
<p>
		
<span class="codefrag computeroutput">rc</span> is a return code (please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
		</p>
		
</li>
	
		
<li>
		
<p>
		
<span class="codefrag computeroutput">lh</span> is a <span class="codefrag computeroutput">LedgerHandle</span> object to manipulate a ledger;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">ctx</span> is control object used for accountability purposes. 
		</p>
		
</li>
	
</ul>
<a name="N102CB"></a><a name="bk_readLedger"></a>
<h3 class="h4"> Reading from ledger </h3>
<p>
    Read calls may request one or more consecutive entries. The following methods belong
    to <span class="codefrag computeroutput">org.apache.bookkeeper.client.LedgerHandle</span>.
    </p>
<p>
   	
<strong>Synchronous read:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public LedgerSequence readEntries(long firstEntry, long lastEntry) 
    throws InterruptedException, BKException
    </span>
	
</p>
<ul>
	
<li>
	
<p>
	
<span class="codefrag computeroutput">firstEntry</span> is the identifier of the first entry in the sequence of entries to read;
	</p>
	
</li>
	
	
<li>
	
<p>
	
<span class="codefrag computeroutput">lastEntry</span> is the identifier of the last entry in the sequence of entries to read;
	</p>
	
</li>
	
</ul>
<p>
   	
<strong>Asynchronous read:</strong>
   	
</p>
<p>
    
<span class="codefrag computeroutput">
	public void asyncReadEntries(long firstEntry, 
            long lastEntry, ReadCallback cb, Object ctx)
    throws BKException, InterruptedException
    </span>
	
</p>
<p>
    It also takes a first and a last entry identifiers. Additionaly, it takes a callback object 
    <span class="codefrag computeroutput">cb</span> and a control object <span class="codefrag computeroutput">ctx</span>. The callback object must implement
    the <span class="codefrag computeroutput">ReadCallback</span> interface in <span class="codefrag computeroutput">org.apache.bookkeeper.client.AsyncCallback</span>, and
	a class implementing it has to implement a method called <span class="codefrag computeroutput">readComplete</span>
	that has the following signature: 
    </p>
<p>
	
<span class="codefrag computeroutput">
	void readComplete(int rc, LedgerHandle lh, LedgerSequence seq, Object ctx)
	</span>    
	
</p>
<p>
	where:
	</p>
<ul>
		
<li>
		
<p>
		
<span class="codefrag computeroutput">rc</span> is a return code (please refer to <span class="codefrag computeroutput">org.apache.bookeeper.client.BKDefs</span> for a list);
		</p>
		
</li>
	
		
<li>
		
<p>
		
<span class="codefrag computeroutput">lh</span> is a <span class="codefrag computeroutput">LedgerHandle</span> object to manipulate a ledger;
		</p>
		
</li>
		
		
<li>
		
<p>
		
<span class="codefrag computeroutput">seq</span> is a <span class="codefrag computeroutput">LedgerSequence</span> object to containing the list of entries requested;
		</p>
		
</li>

		
<li>
		
<p>
		
<span class="codefrag computeroutput">ctx</span> is control object used for accountability purposes. 
		</p>
		
</li>
	
</ul>
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