Re: JIT compiling with LLVM v9.0

On Wed, Jan 31, 2018 at 2:49 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:
>> 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.

Hmm, I guess that's true. I'm not sure that we really need a way to
error out if JIT is not available, but maybe we do.

>> 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...

Agreed.

--
Robert Haas
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