Horton

Re: JIT compiling with LLVM v9.0

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Jeff Davis <pgsql@j-davis.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-01-31T19:49:42Z
Lists: pgsql-hackers 
On 2018-01-31 14:45:46 -0500, Robert Haas wrote:
> On Wed, Jan 31, 2018 at 1:34 PM, Andres Freund <andres@anarazel.de> wrote:
> >> The first one is a problem that's not going to go away.  If the
> >> problem of JIT being enabled "magically" is something we're concerned
> >> about, we need to figure out a good solution, not just disable the
> >> feature by default.
> >
> > That's a fair argument, and I don't really have a good answer to it. We
> > could have a jit = off/try/on, and use that to signal things? I.e. it
> > can be set to try (possibly default in version + 1), and things will
> > work if it's not installed, but if set to on it'll refuse to work if not
> > enabled. Similar to how huge pages work now.
> 
> We could do that, but I'd be more inclined just to let JIT be
> magically enabled.  In general, if a user could do 'yum install ip4r'
> (for example) and have that Just Work without any further database
> configuration, I think a lot of people would consider that to be a
> huge improvement.  Unfortunately we can't really do that for various
> reasons, the biggest of which is that there's no way for installing an
> OS package to modify the internal state of a database that may not
> even be running at the time.  But as a general principle, I think
> having to configure both the OS and the DB is an anti-feature, and
> that if installing an extra package is sufficient to get the
> new-and-improved behavior, users will like it.

I'm not seing a contradiction between what you describe as desired, and
what I describe?  If it defaulted to try, that'd just do what you want,
no? I do think it's important to configure the system so it'll error if
JITing is not available.


> Bonus points if it doesn't require a server restart.

I think server restart might be doable (although it'll increase memory
usage because the shlib needs to be loaded in each backend rather than
postmaster), but once a session is running I'm fairly sure we do not
want to retry. Re-checking whether a shlib is available on the
filesystem every query does not sound like a good idea...

Greetings,

Andres Freund

Commits

  1. Improve JIT docs.

  2. Add documentation for the JIT feature.

  3. Add EXPLAIN support for JIT.

  4. Add inlining support to LLVM JIT provider.

  5. JIT tuple deforming in LLVM JIT provider.

  6. Add FIELDNO_* macro designating offset into structs required for JIT.

  7. Add expression compilation support to LLVM JIT provider.

  8. Expand list of synchronized types and functions in LLVM JIT provider.

  9. Add helpers for emitting LLVM IR.

  10. Basic planner and executor integration for JIT.

  11. Debugging and profiling support for LLVM JIT provider.

  12. Support for optimizing and emitting code in LLVM JIT provider.

  13. Add file containing extensions of the LLVM C API.

  14. Basic JIT provider and error handling infrastructure.

  15. Add configure infrastructure (--with-llvm) to enable LLVM support.

  16. Add C++ support to configure.

  17. Add PGAC_PROG_VARCC_VARFLAGS_OPT autoconf macro.

  18. Fix VM buffer pin management in heap_lock_updated_tuple_rec().

  19. Allow tupleslots to have a fixed tupledesc, use in executor nodes.

  20. Expression evaluation based aggregate transition invocation.

  21. Perform slot validity checks in a separate pass over expression.

  22. Rely on executor utils to build targetlist for DML RETURNING.

  23. Refer to OS X as "macOS", except for the port name which is still "darwin".