[Pljava-dev] Questions about pl/java

Hi Chris,
Some answers from the 'developers of pl/java' side.

Chris Hoover wrote:
> Hello,
>
> I am new to pl/java and have some basic questions. But before the
> questions, a bit about my setup. We are in the process of migrating all
> of our databases from 7.3.4 to 8.1.1. When this is done, we will have
> all of our database servers on RH AS 4.0 with PG 8.1.1.
>
If your migration hasn't been done yet, I'd seriously consider using PG
8.1.3 (the latest release). See:

http://www.postgresql.org/about/news.476
http://www.postgresql.org/about/news.456

> 3. Do the developers of pl/java consider it production quality?
>
Yes, but as with every OSS known that I know of, there's a disclaimer in
the license agreement (standard BSD) that might be worth reading (the
upper cased part): http://wiki.tada.se/display/pljava/PLJava+License

> 4. Can the pl/java be used to communicate across databases?
>
Yes. PL/Java is particularly well suited for this since you can register
listeners that get notified when a transaction commits or rolls back.
The Java runtime, with it's extensive Socket I/O capabilities, is an
excellent platform to build this kind of things on.

> 5. How different is writing in pl/java versus writing application/web
> java programs?
>
Well, Java is Java. PL/Java is no different in that respect. There are
two major things to consider when implementing code for PL/Java:
1. PL/Java code is executed "inside" of transaction, i.e. no commit nor
rollback available.
2. Code is isolated to one single session, i.e. you can never share data
with other sessions.

> 6. Are the any limitations or major pluses on what pl/java can do
> versus pl/pgsql?
>
## The major pluses: ##

** Base your code on the Java Runtime packages
The Java runtime includes XML-parsers, Networking, Collections, Logging,
and a lot of other things that make life easy for a programmer.

** Use Open Source libraries in your code
If you lack something in hte Java Runtime, chances are high you'll find
it in an Open Source product that can be downloaded and installed.

** Develop the code using your favorite IDE
Very advanced (and free) Interactive Development Environments

** Source line debugging
Attach to a PL/Java enabled session using the standard java debugger or
the more advanced debugger that comes with your IDE.

** Managed complexity
Divide your code into classes, interfaces, packages, and different
projects. Create extensive and complex logic.

** Code Reuse
Reuse utility classes that is used in other parts or your application

** Compatibility
The code that you write will be very easy to port to other databases
that support Java stored procedures, functions, and triggers.

** All other advantages using a OO language

## Limitations: ##

** Resource demanding
At present, each session that uses PL/Java will instantiate it's own
JVM. While this has advantages such as very low call overhead and an
extremely high level of isolation, it has drawbacks such as high memory
consumption and a long startup time. PL/Java performs best when it is
used in conjunction with a connection pool. I would not recommend
PL/Java if you expect a high number of fairly short-lived connections.

I'm working on complementing PL/Java with a solution where all sessions
share a remote JVM. The call overhead will increase but memory
consumption and startup times will decrease significantly. I expect both
types of solutions to be in the product. And no, sorry, no time estimate
for that.

** Overly complex for very simple tasks
Java code needs to be compiled, packaged in a jar file, and installed
into the database. pgsql code is embedded in the function declaration.

** Project stability
PL/Java is young, not that widespread, and maintained by a few outside
of the PostgreSQL core project. PL/pgsql is the opposite on all counts.

> Thanks so much for any information you can provide me. I am looking at
> the documentation, but I am a small time crunch.
>
Aren't we all ;-)

Kind Regards,
Thomas Hallgren