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<title>PL/Java and PosgreSQL 8</title>
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<h1>PL/Java and PostgreSQL 8.0</h1>
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<p><font size="2">Java™ is a registered trademark of Sun Microsystems, Inc. in the United States and other countries.</font></p><br/>
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<p>PostgreSQL introduces a couple of new features that PL/Java make use of.</p>
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<h2>Exception handling</h2>
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<p>It is now possible to catch and handle an exception in the Postgres backend.
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While it was possible to catch an exception in earlier Postgres versions as
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well, there was no way to prevent the generated message from being printed, nor
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to find out what the error was. The nested transaction concept introduced with
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8.0 forced this to change and Postgres introduced a try/catch system and a
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structure called <code>ErrorData</code> that can be used when investigating the
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cause of an exception. PL/Java fully exploits this. The <code>ErrorData</code> is
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exposed as a property in a class called <code>
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org.postgresql.pljava.ServerException</code> (derived from
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<code>java.sql.SQLException</code>) and the Java try/catch mechanism is
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synchronized with the backend mechanism.</p>
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PostgreSQL savepoints are exposed using the <code>java.sql.Connection</code>
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interface. Two restrictions apply.<ul>
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<li>A savepoint must be rolled back or released in the function where it was
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<li>A savepoint must not outlife the function where it was set</li>
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<h2>Module configuration.</h2>
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<p>Postgres 8.0 introduces the concept of <i>custom variable classes</i> in the
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<code>postgresql.conf</code> configuration file to enable modules like PL/Java to
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add their own configuration parameters. Normally, any variable name that the
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postmaster cannot recognize will generate an error. Now, with a custom variable
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class, a module can add a class of variables that the postmaster will accept.
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It's then up to the module to verify their correctness.</p>
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<p>Please note that custom variables can be set using the SQL SET command also,
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just like most other variables.</p>
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<p>PL/Java introduces a custom variable class named "pljava" and some variables.
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Here's a sample postgresql.conf entry using all (3) of the variables currently
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<pre># define "pljava" as a custom variable class. This is a comma separated
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custom_variable_classes = 'pljava'
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# define the class path that the JVM will use when loading the
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# initial library. Only meaningful for non GJC installations
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pljava.classpath = '/home/Tada/pljava/build/pljava.jar'
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# Set the size of the prepared statement MRU cache
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pljava.statement_cache_size = 10
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# If true, lingering savepoints will be released on function exit. If false,
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# the will be rolled back
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pljava.release_lingering_savepoints = true
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# Define startup options for the Java VM.
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pljava.vmoptions = '-Xmx64M'
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# Setting debug to true will cause the postgres process to go
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# into a sleep(1) loop on its first call to java. This is
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# only useful if you want to debug the PL/Java internal C code.
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pljava.debug = false</pre>
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