Horton

Re: JIT compiling with LLVM v9.0

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>
Date: 2018-01-30T20:06:02Z
Lists: pgsql-hackers 
On Tue, Jan 30, 2018 at 2:08 PM, Andres Freund <andres@anarazel.de> wrote:
>> That bites, although it's probably tolerable if we expect such errors
>> only in exceptional situations such as a needed shared library failing
>> to load or something. Killing the session when we run out of memory
>> during JIT compilation is not very nice at all.  Does the LLVM library
>> have any useful hooks that we can leverage here, like a hypothetical
>> function LLVMProvokeFailureAsSoonAsConvenient()?
>
> I don't see how that'd help if a memory allocation fails? We can't just
> continue in that case? You could arguably have reserve memory pool that
> you release in that case and then try to continue, but that seems
> awfully fragile.

Well, I'm just asking what the library supports.  For example:

https://curl.haxx.se/libcurl/c/CURLOPT_PROGRESSFUNCTION.html

If you had something like that, you could arrange to safely interrupt
the library the next time the progress-function was called.

> The ones I looked at just error out.  Needing to handle OOM in soft fail
> manner isn't actually that common a demand, I guess :/.

Bummer.

> I mean we could periodically rescan, rescan after sighup, or such? But
> that seems like something for later to me. It's not going to be super
> common to install new extensions while a lot of sessions are
> running. And things will work in that case, the functions just won't get inlined...

Fair enough.

>> > Do people feel these should be hidden behind #ifdefs, always present but
>> > prevent from being set to a meaningful, or unrestricted?
>>
>> We shouldn't allow non-superusers to set any GUC that dumps files to
>> the data directory or provides an easy to way to crash the server, run
>> the machine out of memory, or similar.
>
> I don't buy the OOM one - there's so so so many of those already...
>
> The profiling one does dump to ~/.debug/jit/ - it seems a bit annoying
> if profiling can only be done by a superuser? Hm :/

The server's ~/.debug/jit?  Or are you somehow getting the output to the client?

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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".