Re: JIT compiling with LLVM v11

On 3/9/18 15:56, Andres Freund wrote:
> On 2018-03-09 15:28:19 -0500, Peter Eisentraut wrote:
>> On 3/6/18 15:16, Andres Freund wrote:
>>> 2) Don't load the JIT provider until fully needed. Right now
>>> jit_compile_expr() will load the jit provider even if not really
>>> needed. We should probably move the first two return blocks in
>>> llvm_compile_expr() into jit_compile_expr(), to avoid that.
>>
>> I see that you have implemented that, but it doesn't seem to have helped
>> with my make installcheck times.
>
> What's the exact comparison you're looking at?

I'm just running `time make installcheck` with default settings, as
described in my message from March 6.

> I think that's largely that unnecessary trivial queries get JITed and
> optimized, because the stats are entirely completely off.

Right. I instrumented this a bit, and there are indeed two handfuls of
queries that exceed the default JIT thresholds, as well as a few that
trigger JIT because they disable some enable_* planner setting, as
previously discussed.

Should we throw in some ANALYZEs to avoid this?

If I set jit_expressions = off, then the timings match again.

It's perhaps a bit confusing that some of the jit_* settings take effect
at plan time and some at execution time. At the moment, this mainly
affects me reading the code ;-), but it would also have some effect on
prepared statements and such.

Also, jit_tuple_deforming is apparently used only when jit_expressions
is on.

So, we should work toward more clarity on all these different settings,
what they are useful for, when to set them, how they interact.

--
Peter Eisentraut http://www.2ndQuadrant.com/
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