PL/Java readme

PL/Java, 1.2.x

Java™ is a registered trademark of Sun Microsystems, Inc. in the United States and other countries.

A source tarball and four of binary builds can be found in the download area. Two for Windows and two for i386 based Linux. Although all pre-compiled binaries must run using a standard JVM, the PL/Java can also be compiled and linked using GNU GCJ. PL/Java has no pre-compiled binaries for GCJ but the make system contain what’s needed to make the build easy.

Please note that all use of GCJ should be regarded as experimental. Due to limitations in the implementation of in some versions of GCJ the PL/Java trusted language implementation is, in fact, not trusted. At present this applies regardless of what GCJ version since the code is conditionally compiled.


  • PostgreSQL >= 8.0.3
  • PostgreSQL JDBC drivers (needed by the client Deployer program).
  • A Java runtime >= Java 1.4 or GCJ >= 4.0.x (Linux only).

Get the binary distribution of PL/Java for your platform. Unzip it into a directory of your own choice.

Postmaster configuration

Get the PostgreSQL environment up and running. You will need to modify the postgresql.conf file. In order to find the PL/Java shared object, you can do one of two things. Either you install the shared object in a directory already searched by the postmaster (such as the data directory) or you tell the postmaster where to find it using the dynamic_library_path. I.e. you have a setting similar to this:

dynamic_library_path = '$libdir:<pljava installation>'

Note that on the win32 platform you need to use a semicolon as a path separator and double backslashes (since backslash is the escape character in the postgresql.conf file) as directory separators.

In order to see the logging from the tests add the following:

log_min_messages = info

Add the following entry:

custom_variable_classes = 'pljava'

System classpath

Normally, all Java code is loaded into the database using the install_jar/replace_jar SQL functions. Most of PL/Java (those functions included) is however implemented in Java. Unless you use GCJ, where this Java code is compiled and linked with the pljava shared object module, this hen and egg problem needs to be resolved using the system classpath. Add the following entry to the postgresql.conf file:

pljava.classpath = <pljava installation>/pljava.jar

Shared object issues

Unless you use GCJ, the postmaster must be made aware of the location of the shared objects used by the Java Runtime Environment (JRE). Please note that this applies to the postmaster, i.e. the backend process, and not to the client. The client will not need these settings.


Setting the LD_LIBRARY_PATH environment will work on most Linux/Unix platforms:

export LD_LIBRARY_PATH=$JAVA_HOME/jre/lib/i386:$JAVA_HOME/jre/lib/i386/client.

Apparently, on some Linux platforms you will also need to include $JAVA_HOME/jre/lib/i386/native_threads.

An alternative to use LD_LIBRARY_PATH is to edit the /etc/ file and then use /sbin/ldconfig on some Linux/Unix systems.

zlib conflict

On some platforms there will be a conflict between the included in the JRE and the used by PostgreSQL (the JRE includes a The symptom is an InternalError in the when an attempt is made to load the first class. You can verify the version of using the following command:

strings | fgrep Copyright

The problem can be resolved in one of the following ways depending on your needs and ability to recompile:

  • Check if you can use a newer version of your JRE where the versions match. If so, that’s probably the best solution.
  • Set the environment LD_PRELOAD in effect for the postmaster process to point to the present in the JRE. That will force the JRE version to be used. This might break postgres own use of compression for the affected processes.
  • Reconfigure PostgreSQL with –without-zlib, recompile and reinstall. This will effetively disable all compression support in PostgreSQL.
  • Obtain a zlib version from somewhere that corresponds to the version used by the JRE and relink your PostgreSQL executables with that version.


A standard install on a Windows box would be to add the following entries to you PATH environment:

set PATH=%PATH%;%JAVA_HOME%\jre\bin;%JAVA_HOME%\jre\bin\client

You are now ready to start the postmaster.

Deploying the PL/Java

PL/Java adds a schema named SQLJ to the database (the naming is from the proposed SQL standard for Java backend mapping) and adds a couple of tables and functions to that schema. The deployment can be done in one of two ways. The simplest way is probably to just execute the file install.sql as a super user (the uninstall.sql will remove the PL/Java installation). PL/Java also comes with deploy program that lets you install, reinstall, or uninstall PL/Java. This program will assert that you indeed are a super user and then execute the correct commands using jdbc. In order to run this program, you must see to that the PostgreSQL jdbc driver package postgresql.jar and the deploy.jar file is in your CLASSPATH, then run:

java org.postgresql.pljava.deploy.Deployer
This will result in a list of options. Typically you would use something like:
java org.postgresql.pljava.deploy.Deployer -install

That’s all there’s to it. You are now ready to start using the PL/Java system.

Run the example tests

The tests are divided into two jar files. One is the client part found in the test.jar. It contains some methods that executes SQL statements and prints the output (all contained there can of course also be executed from psql or any other client). The other is the examples.jar which contains the sample code that runs in the backend. The latter must be installed in the database in order to function. An easy way to do this is to use psql and issue the command:

SELECT sqlj.install_jar('file:///some/directory/examples.jar', 'samples',  true);

Please note that the deployment descriptor stored in examples.jar will attempt to create the schema javatest so the user that executes the sqlj.install_jar must have permission to do that. If this command succeeds, everything is working correctly. You may get a couple of errors here though.

  • A complaint that the class org.postgresql.pljava.<something> cannot be found.
    The probable cause of this is that the CLASSPATH seen by the postmaster is incorrect so that the pljava.jar is not found.
  • A complaint that the or pljava.dll cannot be found. Probable cause is that the dynamic_library_path in the postgresql.conf file is incorrect.

Once loaded, you must also set the classpath used by the PL/Java runtime. This classpath is set per schema (namespace). A schema that lacks a classpath will default to the classpath that has been set for the public schema. The tests will use the schema javatest. To define the classpath for this schema, simply use psql and issue the command:

SELECT sqlj.set_classpath('javatest', 'samples');

The first argument is the name of the schema, the second is a colon separated list of jar names. The names must reflect jars that are installed in the system.

NOTE: If you don’t use schemas, you must still issue the set_classpath command to assign a correct classpath to the ‘public’ schema. This can only be done by a super user.


Now, you should be able to run the tests:

java org.postgresql.pljava.test.Tester


Building should be very stright forward:

  • No PosgreSQL source is needed. Your path must be set to find the pg_config binary. The ‘pgxs’ concept in PostgreSQL will take care of the rest.
  • If you are using GCJ, you must supply USE_GCJ=1 to the make command.
  • If you are using a normal Java VM, be sure to set the JAVA_HOME environment variable.