[Pljava-dev] Re: [ANNOUNCE] ANN: PLJava 1.0.0 released

[Thomas Hallgren]

Péter,

> Are the java classes run in a bytecode-interpreted mode or are they 
> compiled into native code using HotSpot or similar?

That depends on the JVM. The Sun JVM will detect hotspots and do JIT 
compilations as needed. The same goes for JRockit.

If you use GCJ, then the current version will utilize native code for 
pljava's own Java code and the stuff loaded with install_jar will be 
interpreted. This is of course subject to improvement. You can preload 
precompiled .so files also, the same way the pljava.so is loaded, but 
that circumvents the normal classloader semantics.

> Does the one session - one JVM archticture means that a large number 
> of sessions require large number of memory. E.g. 200 session needs ca. 
> 200*30MB = 6GB memory?

Since the backend is single-threaded and starts a new process for each 
session, there's no way to have multiple sessions running in one JVM 
unless some inter-process communication protocoll is added. Please read 
the rationale behind choice of technology here: 
http://gborg.postgresql.org/project/pljava/genpage.php?jni_rationale.

The pl-j project at http://plj.codehaus.org took another approach. They 
use one JVM and instead suffer from the IPC overhead.

 From a pure "java-in-the-backend" perspective, it would have been 
better if the postmaster spawned threads rather than processes. There 
are many other perspectives though as you will find out if you bring the 
subject up on one of the PostgreSQL mailing lists :-)

Regards,
Thomas Hallgren