Re: WIP: Faster Expression Processing and Tuple Deforming (including JIT)

Andres Freund <andres(at)anarazel(dot)de> writes:
> On 2016-12-06 13:56:28 -0500, Tom Lane wrote:
>> I guess the $64 question that has to be addressed here is whether we're
>> prepared to accept LLVM as a run-time dependency. There are some reasons
>> why we might not be:

> Indeed. It'd only be a soft dependency obviously.

Oh, so we'd need to maintain both the LLVM and the traditional expression
execution code? That seems like a bit of a pain, but maybe we can live
with it.

>> * How will we answer people who say they can't accept having a compiler
>> installed on their production boxes for security reasons?

> I think they'll just not enable --with-llvm in that case, and get
> inferior performance. Note that installing llvm does not imply
> installing a full blown C compiler (although I think that's largely
> moot, you can get pretty much the same things done with just compiling
> LLVM IR).

I'm not entirely thrilled with the idea of this being a configure-time
decision, because that forces packagers to decide for their entire
audience whether it's okay to depend on LLVM. That would be an untenable
position to put e.g. Red Hat's packagers in: either they screw the people
who want performance or they screw the people who want security.

I think it'd be all right if we can build this so that the direct
dependency on LLVM is confined to a separately-packageable extension.
That way, a packager can produce a core postgresql-server package
that does not require LLVM, plus a postgresql-llvm package that does,
and the "no compiler please" crowd simply doesn't install the latter
package.

The alternative would be to produce two independent builds of the
server, which I suppose might be acceptable but it sure seems like
a kluge, or at least something that simply wouldn't get done by
most vendors.

regards, tom lane