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<title>Persistence for Hashtables</title>
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<h1><dt><font size="+4">Persistence</font></dt>
</h1>
<h2>Using Persistence</h2>
<ul>
<li>The package is meant for users who need to maintain the state of their
Serializable name-value pair sets for better fault tolerance. Using this package
will improve usability but will affect performance depending on the usage
of the persist API.</li>
<li>The current package will support only 2 known implementations, the
DB storage way (which is vendor independant) and an ad-hoc (or some open
source) implementation.</li>
<li>The Persistence package assumes that the user will provide appropriate
properties to initialize and use the storage mechanism.</li>
</ul>
<h2>Code Example</h2>
Code examples make it easy to comprehend the package.
<p><samp><font face="Courier New, Courier, monospace"><code><br>
</code></font></samp></p>
<font face="Courier New, Courier, monospace">import org.jgroups.persistence.*;</font>
<br>
<br>
<font face="Courier New, Courier, monospace">// getting default factor</font><br>
<dt><font face="Courier New, Courier, monospace"><b>PersistenceFactory</b>
<b>factory</b> = <b>PersistenceFactory();</b><br>
</font></dt>
<dt><font face="Courier New, Courier, monospace">//get reference to
PersistenceManager (handle Exception as required by application)</font></dt>
<dt><font face="Courier New, Courier, monospace">// if user defines own properties</font></dt>
<dt><font face="Courier New, Courier, monospace"> try</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> String
filepath = "/home/user/userdefined.properties"</font></dt>
<dt><font face="Courier New, Courier, monospace"> <b>PersistenceManager
manager = factory.createPersistenceManager(filepath);</b></font></dt>
<dt><font face="Courier New, Courier, monospace"> <br>
//if user used existing properties by filling the values
(default properties)</font></dt>
<dt><font face="Courier New, Courier, monospace"> // <b>PersistenceManager
manager = factory.createPersistenceManager();</b></font></dt>
<dt><font face="Courier New, Courier, monospace">}catch (Exception e)</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> //handle
Exception</font></dt>
<dt><font face="Courier New, Courier, monospace">}</font></dt>
<dt><br>
</dt>
<dt><br>
</dt>
<dt><font face="Courier New, Courier, monospace">//once the persistencemanager
reference is obtained, use available</font></dt>
<dt><font face="Courier New, Courier, monospace">// to save a NV</font></dt>
<dt><font face="Courier New, Courier, monospace">HashMap map = new HashMap();</font></dt>
<dt><font face="Courier New, Courier, monospace">map.put("bela", "bela");</font></dt>
<dt><font face="Courier New, Courier, monospace">map.put("mandar", "mandar");</font></dt>
<dt><font face="Courier New, Courier, monospace">try</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> <b>manager.saveAll(map);</b>
// will store all values from map into storage</font></dt>
<dt><font face="Courier New, Courier, monospace">}catch (CannotPersistException
cpe)</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> //handle
exception</font></dt>
<dt><font face="Courier New, Courier, monospace">}</font></dt>
<dt><br>
</dt>
<dt><br>
</dt>
<dt><font face="Courier New, Courier, monospace">//to update a value;</font></dt>
<dt><font face="Courier New, Courier, monospace">try</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> map.put("bela",
"geek");</font></dt>
<dt><font face="Courier New, Courier, monospace"> <b>manager.save("bela",
"geek");</b>
// will update { {bela,bela}, {mandar,mandar})</font></dt>
<dt><font face="Courier New, Courier, monospace">
// to { {bela,geek},
{mandar,mandar})</font></dt>
<dt><font face="Courier New, Courier, monospace">}catch (CannotPersistException
cpe)</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> //handle
exception</font></dt>
<dt><font face="Courier New, Courier, monospace">}</font></dt>
<dt><br>
</dt>
<dt><br>
</dt>
<dt><font face="Courier New, Courier, monospace">// to remove an entry</font></dt>
<dt><font face="Courier New, Courier, monospace">try</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> <b>map.remove("mandar");</b></font></dt>
<dt><font face="Courier New, Courier, monospace"> String
value = (String) <b>manager.remove("mandar");</b>// will update {{bela,geek},
{mandar, mandar}}</font></dt>
<dt><font face="Courier New, Courier, monospace"> //use
value if required
// to {bela,geek}</font></dt>
<dt><font face="Courier New, Courier, monospace">}catch (CannotRemoveException
cre)</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> // handle
exception</font></dt>
<dt><font face="Courier New, Courier, monospace">}</font></dt>
<dt><br>
</dt>
<dt><font face="Courier New, Courier, monospace">//**************************************************************************</font></dt>
<dt><br>
</dt>
<dt><font face="Courier New, Courier, monospace">// say, at start of application
, need to get back stored state</font></dt>
<dt><font face="Courier New, Courier, monospace">//use above example to get
back reference to "manager"</font></dt>
<dt><font face="Courier New, Courier, monospace">try</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> HashMap
map = (HashMap) <b>manager.retrieveAll();</b> // map will
get {{bela,geek}}</font></dt>
<dt><font face="Courier New, Courier, monospace">}catch (CannotRetrieveException
cree)</font></dt>
<dt><font face="Courier New, Courier, monospace">{</font></dt>
<dt><font face="Courier New, Courier, monospace"> // handle
exception</font></dt>
<dt><font face="Courier New, Courier, monospace">}</font></dt>
<dt><br>
</dt>
<h2>Entering Properties (persist.properties)</h2>
Currently, the properties reflect only the DB related, as the FILE based implementation
is not in place.<br>
<table border="1" cols="3" width="100%" nosave="">
<tbody>
<tr>
<td>Name</td>
<td>Description</td>
<td>Typical Value</td>
</tr>
<tr>
<td>persist</td>
<td>Used to decide between DB or FILE.</td>
<td>DB/FILE (No default assumed)</td>
</tr>
<tr>
<td>jdbc.table</td>
<td>Lets the user dictate the schema used to storage purposes on the
database.</td>
<td>create table replhashmap(key varchar(100), keybin blob, valbin
blob) </td>
</tr>
<tr>
<td>jdbc.Driver</td>
<td>Classname for driver that needs to be loaded for DB storage.</td>
<td>oracle.jdbc.driver.OracleDriver</td>
</tr>
<tr>
<td>jdbc.Conn</td>
<td>Connection string required for user to connect to Db instance</td>
<td>jdbc:oracle:oci8:@instance</td>
</tr>
<tr>
<td>jdbc.User</td>
<td>User name required to connect to provided DB instance</td>
<td>user</td>
</tr>
<tr>
<td>jdbc.Pass</td>
<td>Password wrt to User provided</td>
<td>pass</td>
</tr>
</tbody>
</table>
<dt><br>
</dt>
<dt><br>
</dt>
<dt><br>
</dt>
<h2>Using org.jgroups.blocks.DistributedHashtable with PersistenceManager</h2>
<dt>// Example of how to setup and use DistributedHashtable<br>
</dt>
<ul>
<li>Create persist.properties (classpath or home dir)<br>
</li>
<li>Start one instance with -persist</li>
<li>Start another instance with -persist</li>
<li>Add a couple of values</li>
<li>Delete both instances</li>
<li>Start first instance again: previous values should be available</li>
</ul>
<br>
<dt><br>
</dt>
<dt><br>
</dt>
<dt><br>
</dt>
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