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From rake...@apache.org
Subject svn commit: r1759132 [27/42] - in /zookeeper/site/trunk: content/ content/doc/r3.4.9/ content/doc/r3.4.9/api/ content/doc/r3.4.9/api/org/ content/doc/r3.4.9/api/org/apache/ content/doc/r3.4.9/api/org/apache/zookeeper/ content/doc/r3.4.9/api/org/apache/...
Date Sat, 03 Sep 2016 20:33:32 GMT
Added: zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperOverview.html
URL: http://svn.apache.org/viewvc/zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperOverview.html?rev=1759132&view=auto
==============================================================================
--- zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperOverview.html (added)
+++ zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperOverview.html Sat Sep  3 20:33:30 2016
@@ -0,0 +1,694 @@
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+<h1>BookKeeper overview</h1>
+<div id="front-matter">
+<div id="minitoc-area">
+<ul class="minitoc">
+<li>
+<a href="#bk_Overview">BookKeeper overview</a>
+<ul class="minitoc">
+<li>
+<a href="#bk_Intro">BookKeeper introduction</a>
+</li>
+<li>
+<a href="#bk_moreDetail">In slightly more detail...</a>
+</li>
+<li>
+<a href="#bk_basicComponents">Bookkeeper elements and concepts</a>
+</li>
+<li>
+<a href="#bk_initialDesign">Bookkeeper initial design</a>
+</li>
+<li>
+<a href="#bk_metadata">Bookkeeper metadata management</a>
+</li>
+<li>
+<a href="#bk_closingOut">Closing out ledgers</a>
+</li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+  
+
+  
+  
+<a name="bk_Overview"></a>
+<h2 class="h3">BookKeeper overview</h2>
+<div class="section">
+<a name="bk_Intro"></a>
+<h3 class="h4">BookKeeper introduction</h3>
+<p>
+	BookKeeper is a replicated service to reliably log streams of records. In BookKeeper, 
+	servers are "bookies", log streams are "ledgers", and each unit of a log (aka record) is a 
+	"ledger entry". BookKeeper is designed to be reliable; bookies, the servers that store 
+	ledgers, can crash, corrupt data, discard data, but as long as there are enough bookies 
+	behaving correctly the service as a whole behaves correctly.
+	</p>
+<p>
+    The initial motivation for BookKeeper comes from the namenode of HDFS. Namenodes have to 
+    log operations in a reliable fashion so that recovery is possible in the case of crashes. 
+    We have found the applications for BookKeeper extend far beyond HDFS, however. Essentially, 
+    any application that requires an append storage can replace their implementations with
+    BookKeeper. BookKeeper has the advantage of scaling throughput with the number of servers. 
+    </p>
+<p>
+    At a high level, a bookkeeper client receives entries from a client application and stores it to
+    sets of bookies, and there are a few advantages in having such a service:
+	</p>
+<ul>
+    
+<li>
+    
+<p>
+    	We can use hardware that is optimized for such a service. We currently believe that such a
+      	system has to be optimized only for disk I/O;
+    </p>
+    
+</li>
+    
+    
+<li>
+    
+<p>
+    	We can have a pool of servers implementing such a log system, and shared among a number of servers;
+    </p>
+    
+</li>
+    
+    
+<li>
+    
+<p>
+    	We can have a higher degree of replication with such a pool, which makes sense if the hardware necessary for it is cheaper compared to the one the application uses. 
+	</p>
+	
+</li>
+	
+</ul>
+<a name="bk_moreDetail"></a>
+<h3 class="h4">In slightly more detail...</h3>
+<p> BookKeeper implements highly available logs, and it has been designed with write-ahead logging in mind. Besides high availability
+    due to the replicated nature of the service, it provides high throughput due to striping. As we write entries in a subset of bookies of an
+    ensemble and rotate writes across available quorums, we are able to increase throughput with the number of servers for both reads and writes. 
+    Scalability is a property that is possible to achieve in this case due to the use of quorums. Other replication techniques, such as 
+    state-machine replication, do not enable such a property. 
+    </p>
+<p> An application first creates a ledger before writing to bookies through a local BookKeeper client instance.   
+  	Upon creating a ledger, a BookKeeper client writes metadata about the ledger to ZooKeeper. Each ledger currently 
+  	has a single writer. This writer has to execute a close ledger operation before any other client can read from it. 
+  	If the writer of a ledger does not close a ledger properly because, for example, it has crashed before having the 
+  	opportunity of closing the ledger, then the next client that tries to open a ledger executes a procedure to recover
+  	it. As closing a ledger consists essentially of writing the last entry written to a ledger to ZooKeeper, the recovery
+  	procedure simply finds the last entry written correctly and writes it to ZooKeeper.	
+	</p>
+<p>
+	Note that currently this recovery procedure is executed automatically upon trying to open a ledger and no explicit action is necessary. 
+	Although two clients may try to recover a ledger concurrently, only one will succeed, the first one that is able to create the close znode
+	for the ledger.
+	</p>
+<a name="bk_basicComponents"></a>
+<h3 class="h4">Bookkeeper elements and concepts</h3>
+<p> 
+	BookKeeper uses four basic elements:
+	</p>
+<ul>
+      
+<li>
+      
+<p> 
+		
+<strong>Ledger</strong>: A ledger is a sequence of entries, and each entry is a sequence of bytes. Entries are
+		written sequentially to a ledger and at most once. Consequently, ledgers have an append-only semantics;
+	  </p>
+	  
+</li>
+	
+	  
+<li>
+	  
+<p> 
+		
+<strong>BookKeeper client</strong>: A client runs along with a BookKeeper application, and it enables applications
+		to execute operations on ledgers, such as creating a ledger and writing to it; 
+	  </p>
+	  
+</li> 
+	
+	  
+<li>
+	  
+<p>
+		
+<strong>Bookie</strong>: A bookie is a BookKeeper storage server. Bookies store the content of ledgers. For any given
+		ledger L, we call an <em>ensemble</em> the group of bookies storing the content of L. For performance, we store on
+		each bookie of an ensemble only a fragment of a ledger. That is, we stripe when writing entries to a ledger such that
+		each entry is written to sub-group of bookies of the ensemble.
+	  </p>
+	  
+</li>
+
+	  
+<li>
+	  
+<p> 	
+		
+<strong>Metadata storage service</strong>: BookKeeper requires a metadata storage service to store information related 
+		to ledgers and available bookies. We currently use ZooKeeper for such a task.     
+   	  </p>
+   	  
+</li>
+    
+</ul>
+<a name="bk_initialDesign"></a>
+<h3 class="h4">Bookkeeper initial design</h3>
+<p>
+    A set of bookies implements BookKeeper, and we use a quorum-based protocol to replicate data across the bookies. 
+    There are basically two operations to an existing ledger: read and append. Here is the complete API list 
+    (mode detail <a href="bookkeeperProgrammer.html">
+    	      here</a>):
+	</p>
+<ul>
+	
+<li>
+	
+<p>
+    	Create ledger: creates a new empty ledger; 
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    	Open ledger: opens an existing ledger for reading;
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    	Add entry: adds a record to a ledger either synchronously or asynchronously;
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    Read entries: reads a sequence of entries from a ledger either synchronously or asynchronously 
+	</p>
+    
+</li>
+	
+</ul>
+<p>
+	There is only a single client that can write to a ledger. Once that ledger is closed or the client fails, 
+	no more entries can be added. (We take advantage of this behavior to provide our strong guarantees.) 
+	There will not be gaps in the ledger. Fingers get broken, people get roughed up or end up in prison when
+	books are manipulated, so there is no deleting or changing of entries.
+	</p>
+<table class="ForrestTable" cellspacing="1" cellpadding="4">
+<tr>
+<td>BookKeeper Overview</td>
+</tr>
+<tr>
+<td>
+        
+            <img alt="" src="images/bk-overview.jpg">
+        
+        </td>
+</tr>
+</table>
+<p>
+    A simple use of BooKeeper is to implement a write-ahead transaction log. A server maintains an in-memory data structure
+    (with periodic snapshots for example) and logs changes to that structure before it applies the change. The application 
+    server creates a ledger at startup and store the ledger id and password in a well known place (ZooKeeper maybe). When 
+    it needs to make a change, the server adds an entry with the change information to a ledger and apply the change when 
+    BookKeeper adds the entry successfully. The server can even use asyncAddEntry to queue up many changes for high change
+    throughput. BooKeeper meticulously logs the changes in order and call the completion functions in order.
+	</p>
+<p>
+    When the application server dies, a backup server will come online, get the last snapshot and then it will open the 
+    ledger of the old server and read all the entries from the time the snapshot was taken. (Since it doesn't know the 
+    last entry number it will use MAX_INTEGER). Once all the entries have been processed, it will close the ledger and 
+    start a new one for its use. 
+	</p>
+<p>
+	A client library takes care of communicating with bookies and managing entry numbers. An entry has the following fields:
+	</p>
+<table class="ForrestTable" cellspacing="1" cellpadding="4">
+<caption>Entry fields</caption>
+<title>Entry fields</title>
+	
+	
+<tr>
+  	
+<th>Field</th>
+  	<th>Type</th>
+  	<th>Description</th>
+	
+</tr>
+	
+	
+<tr>
+  	
+<td>Ledger number</td>
+  	<td>long</td>
+  	<td>The id of the ledger of this entry</td>
+	
+</tr>
+	
+<tr>
+  	
+<td>Entry number</td>
+  	<td>long</td>
+  	<td>The id of this entry</td>
+	
+</tr>
+	
+	
+<tr>
+  	
+<td>last confirmed (<em>LC</em>)</td>
+  	<td>long</td>
+  	<td>id of the last recorded entry</td>
+	
+</tr>
+	
+<tr>
+  	
+<td>data</td>
+  	<td>byte[]</td>
+  	<td>the entry data (supplied by application)</td>
+	
+</tr>
+	
+<tr>
+  	
+<td>authentication code</td>
+  	<td>byte[]</td>
+  	<td>Message authentication code that includes all other fields of the entry</td>
+	
+</tr>
+	
+	
+	
+</table>
+<p>
+	The client library generates a ledger entry. None of the fields are modified by the bookies and only the first three 
+	fields are interpreted by the bookies.
+	</p>
+<p>
+	To add to a ledger, the client generates the entry above using the ledger number. The entry number will be one more 
+	than the last entry generated. The <em>LC</em> field contains the last entry that has been successfully recorded by BookKeeper. 
+	If the client writes entries one at a time, <em>LC</em> is the last entry id. But, if the client is using asyncAddEntry, there 
+	may be many entries in flight. An entry is considered recorded when both of the following conditions are met:
+	</p>
+<ul>
+	
+<li>
+    
+<p>
+    	the entry has been accepted by a quorum of bookies
+    </p>
+    
+</li>
+    
+    
+<li>
+    
+<p>
+    	all entries with a lower entry id have been accepted by a quorum of bookies 
+	</p>
+	
+</li>
+    
+</ul>
+<p>
+	
+<em>LC</em> seems mysterious right now, but it is too early to explain how we use it; just smile and move on.
+	</p>
+<p>
+	Once all the other fields have been field in, the client generates an authentication code with all of the previous fields. 
+	The entry is then sent to a quorum of bookies to be recorded. Any failures will result in the entry being sent to a new
+	quorum of bookies.
+	</p>
+<p>
+	To read, the client library initially contacts a bookie and starts requesting entries. If an entry is missing or 
+	invalid (a bad MAC for example), the client will make a request to a different bookie. By using quorum writes, 
+	as long as enough bookies are up we are guaranteed to eventually be able to read an entry.
+	</p>
+<a name="bk_metadata"></a>
+<h3 class="h4">Bookkeeper metadata management</h3>
+<p>
+	There are some meta data that needs to be made available to BookKeeper clients:
+	</p>
+<ul>
+	
+<li>
+	
+<p>
+		The available bookies;
+	</p>
+	
+</li>
+	
+	
+<li>
+	
+<p>
+    	The list of ledgers;
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    	The list of bookies that have been used for a given ledger;
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    	The last entry of a ledger; 
+	</p>
+	
+</li>
+	
+</ul>
+<p>
+	We maintain this information in ZooKeeper. Bookies use ephemeral nodes to indicate their availability. Clients 
+	use znodes to track ledger creation and deletion and also to know the end of the ledger and the bookies that 
+	were used to store the ledger. Bookies also watch the ledger list so that they can cleanup ledgers that get deleted.
+	</p>
+<a name="bk_closingOut"></a>
+<h3 class="h4">Closing out ledgers</h3>
+<p>
+	The process of closing out the ledger and finding the last ledger is difficult due to the durability guarantees of BookKeeper:
+	</p>
+<ul>
+	
+<li>
+	
+<p>
+    	If an entry has been successfully recorded, it must be readable.
+    </p>
+    
+</li>
+    
+    
+<li>
+	
+<p>
+    	If an entry is read once, it must always be available to be read. 
+	</p>
+	
+</li>
+	
+</ul>
+<p>
+	If the ledger was closed gracefully, ZooKeeper will have the last entry and everything will work well. But, if the 
+	BookKeeper client that was writing the ledger dies, there is some recovery that needs to take place.
+	</p>
+<p>
+	The problematic entries are the ones at the end of the ledger. There can be entries in flight when a BookKeeper client 
+	dies. If the entry only gets to one bookie, the entry should not be readable since the entry will disappear if that bookie
+	fails. If the entry is only on one bookie, that doesn't mean that the entry has not been recorded successfully; the other
+	bookies that recorded the entry might have failed.
+	</p>
+<p>
+	The trick to making everything work is to have a correct idea of a last entry. We do it in roughly three steps:
+	</p>
+<ol>
+	
+<li>
+	
+<p>
+		Find the entry with the highest last recorded entry, <em>LC</em>;
+	</p>
+	
+</li>
+	
+	
+<li>
+	
+<p>
+		Find the highest consecutively recorded entry, <em>LR</em>;
+	</p>
+	
+</li>
+	
+	
+<li>
+	
+<p>
+		Make sure that all entries between <em>LC</em> and <em>LR</em> are on a quorum of bookies; 
+	</p>
+	
+</li>
+	
+	
+</ol>
+</div>  
+
+<p align="right">
+<font size="-2"></font>
+</p>
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+        PDF</a>
+</div>
+<h1>BookKeeper Getting Started Guide</h1>
+<div id="front-matter">
+<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>
+<li>
+<a href="#bk_deleteLedger"> Deleting a ledger </a>
+</li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+  
+
+  
+  
+<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>
+      
+      
+<li>
+        
+<p>
+<a href="#bk_deleteLedger"> Deleting a ledger </a>
+</p>
+      
+</li>
+      
+    
+</ul>
+<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 are three BookKeeper constructors:
+    </p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public BookKeeper(String servers) 
+    	throws KeeperException, IOException    
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">servers</span> is a comma-separated list of ZooKeeper servers.
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public BookKeeper(ZooKeeper zk) 
+    	throws InterruptedException, KeeperException    
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">zk</span> is a ZooKeeper object. This constructor is useful when
+        the application also using ZooKeeper and wants to have a single instance of ZooKeeper.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public BookKeeper(ZooKeeper zk, ClientSocketChannelFactory channelFactory) 
+    	throws InterruptedException, KeeperException    
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">zk</span> is a ZooKeeper object. This constructor is useful when
+        the application also using ZooKeeper and wants to have a single instance of ZooKeeper.  
+    	</p>
+    	
+</li>
+    	
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">channelFactory</span> is a netty channel object 
+        (<span class="codefrag computeroutput">org.jboss.netty.channel.socket</span>).  
+    	</p>
+    	
+</li>
+    
+</ul>
+<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, DigestType type,  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">type</span> is the type of digest used with entries: either MAC or CRC32.  
+    	</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 two input parameters it requires are a digest type and a password.
+    </p>
+<p>
+   	
+<strong>Asynchronous call:</strong>
+   	
+</p>
+<p>
+    
+<span class="codefrag computeroutput">
+    public void asyncCreateLedger(int ensSize, 
+            int qSize, 
+            DigestType type,  
+            byte passwd[],
+            CreateCallback cb,
+            Object ctx
+            )
+    </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.BKException</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. It can be essentially any object the application is happy with.
+		</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="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)
+    </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. It can be any object the application is happy with.
+		</p>
+		
+</li>
+	
+</ul>
+<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 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="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, DigestType type, byte passwd[])
+    throws InterruptedException, BKException
+    </span>
+	
+</p>
+<ul>
+	
+<li>
+	
+<p>
+	
+<span class="codefrag computeroutput">ledgerId</span> is the ledger identifier;
+	</p>
+	
+</li>
+	
+	
+<li> 
+    
+<p>
+    
+<span class="codefrag computeroutput">type</span> is the type of digest used with entries: either MAC or CRC32.  
+    </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, DigestType type, byte passwd[], OpenCallback cb, Object ctx)
+    </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="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 Enumeration&lt;LedgerEntry&gt; 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, Enumeration&lt;LedgerEntry&gt; 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">Enumeration&lt;LedgerEntry&gt; </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>
+<a name="bk_deleteLedger"></a>
+<h3 class="h4"> Deleting a ledger </h3>
+<p>
+    Once a client is done with a ledger and is sure that nobody will ever need to read from it again, they can delete the ledger.
+    The following methods belong to <span class="codefrag computeroutput">org.apache.bookkeeper.client.BookKeeper</span>.
+    </p>
+<p>
+   	
+<strong>Synchronous delete:</strong>
+   	
+</p>
+<p>
+    
+<span class="codefrag computeroutput">
+        public void deleteLedger(long lId) throws InterruptedException, BKException
+    </span>
+    
+</p>
+<ul>
+	
+<li>
+	
+<p>
+	
+<span class="codefrag computeroutput">lId</span> is the ledger identifier;
+	</p>
+	
+</li>
+	
+</ul>
+<p>
+   	
+<strong>Asynchronous delete:</strong>
+    
+</p>
+<p>
+      
+<span class="codefrag computeroutput">
+	 public void asyncDeleteLedger(long lId, DeleteCallback cb, Object ctx) 
+      </span>
+    
+</p>
+<p>
+    It takes a ledger identifier. Additionally, 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">DeleteCallback</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">deleteComplete</span>
+	that has the following signature: 
+    </p>
+<p>
+	
+<span class="codefrag computeroutput">
+	void deleteComplete(int rc, 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">ctx</span> is control object used for accountability purposes. 
+		</p>
+		
+</li>
+	
+</ul>
+</div>
+
+<p align="right">
+<font size="-2"></font>
+</p>
+</div>
+<!--+
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+<a class="dida" href="bookkeeperStarted.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br>
+        PDF</a>
+</div>
+<h1>BookKeeper Getting Started Guide</h1>
+<div id="front-matter">
+<div id="minitoc-area">
+<ul class="minitoc">
+<li>
+<a href="#bk_GettingStarted">Getting Started: Setting up BookKeeper to write logs.</a>
+<ul class="minitoc">
+<li>
+<a href="#bk_Prerequisites">Pre-requisites</a>
+</li>
+<li>
+<a href="#bk_Download">Download</a>
+</li>
+<li>
+<a href="#bk_localBK">LocalBookKeeper</a>
+</li>
+<li>
+<a href="#bk_setupBookies">Setting up bookies</a>
+</li>
+<li>
+<a href="#bk_setupZK">Setting up ZooKeeper</a>
+</li>
+<li>
+<a href="#bk_example">Example</a>
+</li>
+</ul>
+</li>
+</ul>
+</div>
+</div>
+  
+
+  
+  
+<a name="bk_GettingStarted"></a>
+<h2 class="h3">Getting Started: Setting up BookKeeper to write logs.</h2>
+<div class="section">
+<p>This document contains information to get you started quickly with
+    BookKeeper. It is aimed primarily at developers willing to try it out, and
+    contains simple installation instructions for a simple BookKeeper installation
+    and a simple programming example. For further programming detail, please refer to 
+    <a href="bookkeeperProgrammer.html">BookKeeper Programmer's Guide</a>.
+    </p>
+<a name="bk_Prerequisites"></a>
+<h3 class="h4">Pre-requisites</h3>
+<p>See <a href="bookkeeperConfig.html#bk_sysReq">
+    	      System Requirements</a> in the Admin guide.</p>
+<a name="bk_Download"></a>
+<h3 class="h4">Download</h3>
+<p> BookKeeper is distributed along with ZooKeeper. To get a ZooKeeper distribution, 
+			   download a recent
+    	    <a href="http://zookeeper.apache.org/releases.html">
+        	  stable</a> release from one of the Apache Download
+       	 Mirrors.</p>
+<a name="bk_localBK"></a>
+<h3 class="h4">LocalBookKeeper</h3>
+<p> Under org.apache.bookkeeper.util, you'll find a java program
+		called LocalBookKeeper.java that sets you up to run BookKeeper on a 
+		single machine. This is far from ideal from a performance perspective,
+		but the program is useful for both test and educational purposes.
+		</p>
+<a name="bk_setupBookies"></a>
+<h3 class="h4">Setting up bookies</h3>
+<p> If you're bold and you want more than just running things locally, then
+		you'll need to run bookies in different servers. You'll need at least three bookies
+		to start with.  
+		</p>
+<p>
+		For each bookie, we need to execute a command like the following:
+		</p>
+<p>
+<span class="codefrag computeroutput">
+		java -cp .:./zookeeper-&lt;version&gt;-bookkeeper.jar:./zookeeper-&lt;version&gt;.jar\
+		:lib/slf4j-api-1.6.1.jar:lib/slf4j-log4j12-1.6.1.jar:lib/log4j-1.2.15.jar -Dlog4j.configuration=log4j.properties\ 
+		org.apache.bookkeeper.proto.BookieServer 3181 127.0.0.1:2181 /path_to_log_device/\
+		/path_to_ledger_device/
+		</span>
+</p>
+<p> "/path_to_log_device/" and "/path_to_ledger_device/" are different paths. Also, port 3181
+		is the port that a bookie listens on for connection requests from clients. 127.0.0.1:2181 is the hostname:port 
+		for the ZooKeeper server. In this example, the standalone ZooKeeper server is running locally on port 2181.
+		If we had multiple ZooKeeper servers, this parameter would be a comma separated list of all the hostname:port
+		values corresponding to them.
+		</p>
+<a name="bk_setupZK"></a>
+<h3 class="h4">Setting up ZooKeeper</h3>
+<p> ZooKeeper stores metadata on behalf of BookKeeper clients and bookies. To get a minimal 
+	  	ZooKeeper installation to work with BookKeeper, we can set up one server running in
+	  	standalone mode. Once we have the server running, we need to create a few znodes:
+	  	</p>
+<ol>
+	  	
+<li>
+	  	
+<p>
+<span class="codefrag computeroutput">
+	  	/ledgers	
+	  	</span>
+</p>
+	  	
+</li>
+	  	
+	  	
+<li>
+	  	
+<p>
+<span class="codefrag computeroutput">
+	  	/ledgers/available
+	  	</span>
+</p>
+	  	
+</li>
+	  	
+	  	
+<li>
+	  	
+<p> For each bookie, we add one znode such that the name of the znode is the
+	  	concatenation of the machine name and the port number that the bookie is 
+	  	listening on. For example, if a bookie is running on bookie.foo.com an is listening 
+	  	on port 3181, we add a znode 
+	  	<span class="codefrag computeroutput">/ledgers/available/bookie.foo.com:3181</span>.  
+	  	</p>
+	  	
+</li>
+	  	
+</ol>
+<a name="bk_example"></a>
+<h3 class="h4">Example</h3>
+<p>
+	    In the following excerpt of code, we:
+	    </p>
+<ol>
+	    	
+<li>
+	    	
+<p>
+	    	Create a ledger;
+	    	</p>
+	    	
+</li>
+	    	
+	    	
+<li>
+	    	
+<p>
+	    	Write to the ledger;
+	    	</p>
+	    	
+</li>
+	    	
+	    	
+<li>
+	    	
+<p>
+	    	Close the ledger;
+	    	</p>
+	    	
+</li>
+	    	
+	    	
+<li>
+	    	
+<p>
+	    	Open the same ledger for reading;
+	    	</p>
+	    	
+</li>
+	    	
+	    	
+<li>
+	    	
+<p>
+	    	Read from the ledger;
+	    	</p>
+	    	
+</li>
+	    	
+	    	
+<li>
+	    	
+<p>
+	    	Close the ledger again;
+	    	</p>
+	    	
+</li>
+	    
+</ol>
+<pre class="code">
+LedgerHandle lh = bkc.createLedger(ledgerPassword);
+ledgerId = lh.getId();
+ByteBuffer entry = ByteBuffer.allocate(4);
+
+for(int i = 0; i &lt; 10; i++){
+	entry.putInt(i);
+	entry.position(0);
+	entries.add(entry.array());				
+	lh.addEntry(entry.array());
+}
+lh.close();
+lh = bkc.openLedger(ledgerId, ledgerPassword);		
+			
+Enumeration&lt;LedgerEntry&gt; ls = lh.readEntries(0, 9);
+int i = 0;
+while(ls.hasMoreElements()){
+	ByteBuffer origbb = ByteBuffer.wrap(
+				entries.get(i++));
+	Integer origEntry = origbb.getInt();
+	ByteBuffer result = ByteBuffer.wrap(
+				ls.nextElement().getEntry());
+
+	Integer retrEntry = result.getInt();
+}
+lh.close();
+	    </pre>
+</div>
+
+<p align="right">
+<font size="-2"></font>
+</p>
+</div>
+<!--+
+    |end content
+    +-->
+<div class="clearboth">&nbsp;</div>
+</div>
+<div id="footer">
+<!--+
+    |start bottomstrip
+    +-->
+<div class="lastmodified">
+<script type="text/javascript"><!--
+document.write("Last Published: " + document.lastModified);
+//  --></script>
+</div>
+<div class="copyright">
+        Copyright &copy;
+         2008-2013 <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a>
+</div>
+<!--+
+    |end bottomstrip
+    +-->
+</div>
+</body>
+</html>

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--- zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperStream.html (added)
+++ zookeeper/site/trunk/content/doc/r3.4.9/bookkeeperStream.html Sat Sep  3 20:33:30 2016
@@ -0,0 +1,612 @@
+<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
+<html>
+<head>
+<META http-equiv="Content-Type" content="text/html; charset=UTF-8">
+<meta content="Apache Forrest" name="Generator">
+<meta name="Forrest-version" content="0.9">
+<meta name="Forrest-skin-name" content="pelt">
+<title>Streaming with BookKeeper</title>
+<link type="text/css" href="skin/basic.css" rel="stylesheet">
+<link media="screen" type="text/css" href="skin/screen.css" rel="stylesheet">
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+<link rel="shortcut icon" href="images/favicon.ico">
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+<body onload="init()">
+<script type="text/javascript">ndeSetTextSize();</script>
+<div id="top">
+<!--+
+    |breadtrail
+    +-->
+<div class="breadtrail">
+<a href="http://www.apache.org/">Apache</a> &gt; <a href="http://zookeeper.apache.org/">ZooKeeper</a> &gt; <a href="http://zookeeper.apache.org/">ZooKeeper</a><script src="skin/breadcrumbs.js" language="JavaScript" type="text/javascript"></script>
+</div>
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+</div>
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+<div class="projectlogo">
+<a href="http://zookeeper.apache.org/"><img class="logoImage" alt="ZooKeeper" src="images/zookeeper_small.gif" title="ZooKeeper: distributed coordination"></a>
+</div>
+<!--+
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+    +-->
+<!--+
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+    +-->
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+                    <input name="Search" value="Search" type="submit">
+</form>
+</div>
+<!--+
+    |end search
+    +-->
+<!--+
+    |start Tabs
+    +-->
+<ul id="tabs">
+<li>
+<a class="unselected" href="http://zookeeper.apache.org/">Project</a>
+</li>
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+</li>
+<li class="current">
+<a class="selected" href="index.html">ZooKeeper 3.4 Documentation</a>
+</li>
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+<div id="publishedStrip">
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+document.write("Last Published: " + document.lastModified);
+//  --></script>
+</div>
+<!--+
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+    +-->
+<div class="breadtrail">
+
+             &nbsp;
+           </div>
+<!--+
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+    +-->
+<!--+
+    |start Menu
+    +-->
+<div id="menu">
+<div onclick="SwitchMenu('menu_1.1', 'skin/')" id="menu_1.1Title" class="menutitle">Overview</div>
+<div id="menu_1.1" class="menuitemgroup">
+<div class="menuitem">
+<a href="index.html">Welcome</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperOver.html">Overview</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperStarted.html">Getting Started</a>
+</div>
+<div class="menuitem">
+<a href="releasenotes.html">Release Notes</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.2', 'skin/')" id="menu_1.2Title" class="menutitle">Developer</div>
+<div id="menu_1.2" class="menuitemgroup">
+<div class="menuitem">
+<a href="api/index.html">API Docs</a>
+</div>
+<div class="menuitem">
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+</div>
+<div class="menuitem">
+<a href="javaExample.html">Java Example</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperTutorial.html">Barrier and Queue Tutorial</a>
+</div>
+<div class="menuitem">
+<a href="recipes.html">Recipes</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.3', 'skin/')" id="menu_1.3Title" class="menutitle">BookKeeper</div>
+<div id="menu_1.3" class="menuitemgroup">
+<div class="menuitem">
+<a href="bookkeeperStarted.html">Getting started</a>
+</div>
+<div class="menuitem">
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+</div>
+<div class="menuitem">
+<a href="bookkeeperConfig.html">Setup guide</a>
+</div>
+<div class="menuitem">
+<a href="bookkeeperProgrammer.html">Programmer's guide</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.4', 'skin/')" id="menu_1.4Title" class="menutitle">Admin &amp; Ops</div>
+<div id="menu_1.4" class="menuitemgroup">
+<div class="menuitem">
+<a href="zookeeperAdmin.html">Administrator's Guide</a>
+</div>
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+</div>
+<div class="menuitem">
+<a href="zookeeperJMX.html">JMX</a>
+</div>
+<div class="menuitem">
+<a href="zookeeperObservers.html">Observers Guide</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.5', 'skin/')" id="menu_1.5Title" class="menutitle">Contributor</div>
+<div id="menu_1.5" class="menuitemgroup">
+<div class="menuitem">
+<a href="zookeeperInternals.html">ZooKeeper Internals</a>
+</div>
+</div>
+<div onclick="SwitchMenu('menu_1.6', 'skin/')" id="menu_1.6Title" class="menutitle">Miscellaneous</div>
+<div id="menu_1.6" class="menuitemgroup">
+<div class="menuitem">
+<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER">Wiki</a>
+</div>
+<div class="menuitem">
+<a href="https://cwiki.apache.org/confluence/display/ZOOKEEPER/FAQ">FAQ</a>
+</div>
+<div class="menuitem">
+<a href="http://zookeeper.apache.org/mailing_lists.html">Mailing Lists</a>
+</div>
+</div>
+<div id="credit"></div>
+<div id="roundbottom">
+<img style="display: none" class="corner" height="15" width="15" alt="" src="skin/images/rc-b-l-15-1body-2menu-3menu.png"></div>
+<!--+
+  |alternative credits
+  +-->
+<div id="credit2"></div>
+</div>
+<!--+
+    |end Menu
+    +-->
+<!--+
+    |start content
+    +-->
+<div id="content">
+<div title="Portable Document Format" class="pdflink">
+<a class="dida" href="bookkeeperStream.pdf"><img alt="PDF -icon" src="skin/images/pdfdoc.gif" class="skin"><br>
+        PDF</a>
+</div>
+<h1>Streaming with BookKeeper</h1>
+<div id="front-matter">
+<div id="minitoc-area">
+<ul class="minitoc">
+<li>
+<a href="#bk_StreamSummary">Summary</a>
+</li>
+<li>
+<a href="#bk_LedgerOutputStream">Writing a stream of bytes</a>
+</li>
+<li>
+<a href="#bk_LedgerInputStream">Reading a stream of bytes</a>
+</li>
+</ul>
+</div>
+</div>
+  
+
+  
+	
+<a name="bk_StreamSummary"></a>
+<h2 class="h3">Summary</h2>
+<div class="section">
+<p>
+    When using the BookKeeper API, an application has to split the data to write into entries, each
+    entry being a byte array. This is natural for many applications. For example, when using BookKeeper
+    for write-ahead logging, an application typically wants to write the modifications corresponding
+    to a command or a transaction. Some other applications, however, might not have a natural boundary
+    for entries, and may prefer to write and read streams of bytes. This is exactly the purpose of the
+    stream API we have implemented on top of BookKeeper.
+    </p>
+<p>
+    The stream API is implemented in the package <span class="codefrag computeroutput">Streaming</span>, and it contains two main classes: <span class="codefrag computeroutput">LedgerOutputStream</span> and 
+    <span class="codefrag computeroutput">LedgerInputStream</span>. The class names are indicative of what they do.
+    </p>
+</div>
+    
+    
+<a name="bk_LedgerOutputStream"></a>
+<h2 class="h3">Writing a stream of bytes</h2>
+<div class="section">
+<p>
+    Class <span class="codefrag computeroutput">LedgerOutputStream</span> implements two constructors and five public methods:
+    </p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public LedgerOutputStream(LedgerHandle lh) 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public LedgerOutputStream(LedgerHandle lh, int size) 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.  
+    	</p>
+    	
+</li>
+
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">size</span> is the size of the byte buffer to store written bytes before flushing.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+   	
+<strong>Closing a stream.</strong> This call closes the stream by flushing the write buffer.
+   	</p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public void close() 
+    </span>
+	
+</p>
+<p>
+    which has no parameters.
+    </p>
+<p>
+   	
+<strong>Flushing a stream.</strong> This call essentially flushes the write buffer.
+   	</p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized void flush() 
+    </span>
+	
+</p>
+<p>
+    which has no parameters.
+    </p>
+<p>
+   	
+<strong>Writing bytes.</strong> There are three calls for writing bytes to a stream.
+   	</p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized void write(byte[] b) 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">b</span> is an array of bytes to write.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized void write(byte[] b, int off, int len) 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">b</span> is an array of bytes to write.  
+    	</p>
+    	
+</li>
+    	
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">off</span> is a buffer offset.  
+    	</p>
+    	
+</li>
+    	
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">len</span> is the length to write.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized void write(int b) 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">b</span> contains a byte to write. The method writes the least significant byte of the integer four bytes.    
+    	</p>
+    	
+</li>
+    
+</ul>
+</div>
+    
+    
+<a name="bk_LedgerInputStream"></a>
+<h2 class="h3">Reading a stream of bytes</h2>
+<div class="section">
+<p>
+    Class <span class="codefrag computeroutput">LedgerOutputStream</span> implements two constructors and four public methods:
+    </p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public LedgerInputStream(LedgerHandle lh)
+	throws BKException, InterruptedException 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public LedgerInputStream(LedgerHandle lh, int size) 
+    throws BKException, InterruptedException
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">lh</span> is a ledger handle for a previously created and open ledger.  
+    	</p>
+    	
+</li>
+
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">size</span> is the size of the byte buffer to store bytes that the application
+        will eventually read.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+   	
+<strong>Closing.</strong> There is one call to close an input stream, but the call
+   	is currently empty and the application is responsible for closing the ledger handle. 
+   	</p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public void close()
+    </span>
+	
+</p>
+<p>
+    which has no parameters.
+    </p>
+<p>
+   	
+<strong>Reading.</strong> There are three calls to read from the stream.
+   	</p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized int read()
+	throws IOException 
+    </span>
+	
+</p>
+<p>
+    which has no parameters.
+    </p>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized int read(byte[] b)
+	throws IOException 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">b</span> is a byte array to write to.  
+    	</p>
+    	
+</li>
+    
+</ul>
+<p>
+    
+<span class="codefrag computeroutput">
+	public synchronized int read(byte[] b, int off, int len)
+	throws IOException 
+    </span>
+	
+</p>
+<p>
+    where:
+    </p>
+<ul>
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">b</span> is a byte array to write to.  
+    	</p>
+    	
+</li>
+    	
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">off</span> is an offset for byte array <span class="codefrag computeroutput">b</span>.  
+    	</p>
+    	
+</li>
+    	
+    	
+<li>
+    	
+<p> 
+        
+<span class="codefrag computeroutput">len</span> is the length in bytes to write to <span class="codefrag computeroutput">b</span>.  
+    	</p>
+    	
+</li>
+    
+</ul>
+</div>
+  
+<p align="right">
+<font size="-2"></font>
+</p>
+</div>
+<!--+
+    |end content
+    +-->
+<div class="clearboth">&nbsp;</div>
+</div>
+<div id="footer">
+<!--+
+    |start bottomstrip
+    +-->
+<div class="lastmodified">
+<script type="text/javascript"><!--
+document.write("Last Published: " + document.lastModified);
+//  --></script>
+</div>
+<div class="copyright">
+        Copyright &copy;
+         2008-2013 <a href="http://www.apache.org/licenses/">The Apache Software Foundation.</a>
+</div>
+<!--+
+    |end bottomstrip
+    +-->
+</div>
+</body>
+</html>

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+<broken-links>
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