On 14 July 2016 at 14:28, Vladimir Sitnikov <sitnikov.vladi...@gmail.com>

> Craig>That moves work further away from the DB, which has its own costs,
> and isn't something you're likely to be happy with if you're looking at
> things like optimising PL/PgSQL with a bytecode compiler. But it's the best
> we have right now.
> What if JVM was started within a background worker?
> Then JVM can spawn several threads that serve PL requests on a "thread per
> backend" basis.

You can't really execute the plpgsql-compiled-to-bytecode outside the user
session, so you need a JVM in it anyway.

You probably could have a bgworker or pool of bgworkers doing your plpgsql
compilation and caching. But because your plpgsql might reference
uncommitted catalog entries in the local backend, you'd the bgworker to
join an exported snapshot from the backend you're compiling the plpgsql
for. If it doesn't let you avoid having a jvm in each backend it's not
likely to be too useful.

Craig>You may be able to greatly reduce that cost if you can store your
> cached compiled data in a shared memory segment created by your extension.
> Craig>This will get a bit easier with the new dynamic shared memory
> infrastructure, but it's going to be no fun at all to make that play with
> the JVM. You'll probably need a lot of JNI.
> There's https://github.com/jnr/jnr-ffi that enables to call C functions
> without resorting to writing JNI wrappers.

Yes, and JNA as well.

 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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