Horton

Re: JIT compiling with LLVM v9.1

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Jeff Davis <pgsql@j-davis.com>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2018-02-03T09:23:14Z
Lists: pgsql-hackers 
Hi,

On 2018-02-03 01:13:21 -0800, Andres Freund wrote:
> On 2018-02-02 18:21:12 -0800, Jeff Davis wrote:
> > I think I saw about a 2% gain here over master, but when I applied it
> > on top of the fast scans it did not seem to add anything on top of
> > fast scans. Seems reproducible, but I don't have an explanation.
> 
> Yea, that makes sense. The primary reason the patch is beneficial is
> that it centralizes the place where the HeapTupleHeader is accessed to a
> single piece of code (slot_deform_tuple()). In a lot of cases that first
> access will result in a cache miss in all layers, requiring a memory
> access. In slot_getsomeattrs() there's very little that can be done in
> an out-of-order manner, whereas slot_deform_tuple() can continue
> execution a bit further. Also, the latter will then go and sequentially
> access the rest (or a significant part of) the tuple, so a centralized
> access is more prefetchable.

Oops missed part of the argument here: The reason that isn't that large
an effect anymore with the scan order patch applied is that suddenly the
accesses are, due to the better scan order, more likely to be cacheable
and prefetchable. So in that case the few additional instructions and
branches in slot_getsomeattrs/slot_getattr don't hurt as much
anymore. IIRC I could still show it up, but it's a much smaller win.

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".