Re: JIT compiling with LLVM v9.0

Hi,

On 2018-01-30 22:57:06 +0100, David Fetter wrote:
> On Tue, Jan 30, 2018 at 01:46:37PM -0500, Robert Haas wrote:
> > On Mon, Jan 29, 2018 at 1:40 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
> > > It's an optional dependency, and it doesn't increase build time
> > > that much... If we were to move the llvm interfacing code to a
> > > .so, there'd not even be a packaging issue, you can just package
> > > that .so separately and get errors if somebody tries to enable
> > > LLVM without that .so being installed.
> >
> > I suspect that would be really valuable. If 'yum install
> > postgresql-server' (or your favorite equivalent) sucks down all of
> > LLVM,
>
> As I understand it, LLVM is organized in such a way as not to require
> this. Andres, am I understanding correctly that what you're using
> doesn't require much of LLVM at runtime?

I'm not sure what you exactly mean. Yes, you need the llvm library at
runtime. Perhaps you're thinking of clang or llvm binarieries? The
latter we *not* need.

What's required is something like:
$ apt show libllvm5.0
Package: libllvm5.0
Version: 1:5.0.1-2
Priority: optional
Section: libs
Source: llvm-toolchain-5.0
Maintainer: LLVM Packaging Team <pkg-llvm-team(at)lists(dot)alioth(dot)debian(dot)org>
Installed-Size: 56.9 MB
Depends: libc6 (>= 2.15), libedit2 (>= 2.11-20080614), libffi6 (>= 3.0.4), libgcc1 (>= 1:3.4), libstdc++6 (>= 6), libtinfo5 (>= 6), zlib1g (>= 1:1.2.0)
Breaks: libllvm3.9v4
Replaces: libllvm3.9v4
Homepage: http://www.llvm.org/
Tag: role::shared-lib
Download-Size: 13.7 MB
APT-Manual-Installed: no
APT-Sources: http://debian.osuosl.org/debian unstable/main amd64 Packages
Description: Modular compiler and toolchain technologies, runtime library
LLVM is a collection of libraries and tools that make it easy to build
compilers, optimizers, just-in-time code generators, and many other
compiler-related programs.
.
This package contains the LLVM runtime library.

So ~14MB to download, ~57MB on disk. We only need a subset of
libllvm5.0, and LLVM allows to build such a subset. But obviously
distributions aren't going to target their LLVM just for postgres.

> > Unfortunately, that has the pretty significant downside that a lot of
> > people who actually want the postgresql-server-jit package will not
> > realize that they need to install it, which sucks.
>
> It does indeed.

With things like apt recommends and such I don't think this is a huge
problem. It'll be installed by default unless somebody is on a space
constrained system and doesn't want that...

Greetings,

Andres Freund