Re: Performance difference in accessing differrent columns in aPostgres Table

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От Jeff Janes
Тема Re: Performance difference in accessing differrent columns in aPostgres Table
Дата
Msg-id CAMkU=1zrdi8Ga21E_ECQ8bP+9+Q7E76gkG5Xj_MLkuCQNm4mDg@mail.gmail.com
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Ответ на Re: Performance difference in accessing differrent columns in aPostgres Table  (Andres Freund <andres@anarazel.de>)
Ответы Re: Performance difference in accessing differrent columns in aPostgres Table
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On Mon, Jul 30, 2018 at 3:02 PM, Andres Freund <andres@anarazel.de> wrote:
Hi,

On 2018-07-30 13:31:33 -0400, Jeff Janes wrote:
> I don't know where the time is going with the as-committed JIT.  None of
> the JIT-specific timings reported by EXPLAIN (ANALYZE) add up to anything
> close to the slow-down I'm seeing.  Shouldn't compiling and optimization
> time show up there?

As my timings showed, I don't see the slowdown you're reporting. Could
you post a few EXPLAIN ANALYZEs?


I don't think you showed any timings where jit_above_cost < query cost < jit_optimize_above_cost, which is where I saw the slow down.  (That is also where things naturally land for me using default settings)

I've repeated my test case on a default build (./configure --with-llvm --prefix=....) and default postgresql.conf, using the post-11BETA2 commit 5a71d3e.


I've attached the full test case, and the full output.

Here are the last two executions, with jit=on and jit=off, respectively.  Doing it with TIMING OFF doesn't meaningfully change things, nor does increasing shared_buffers beyond the default.



                                                        QUERY PLAN
--------------------------------------------------------------------------------------------------------------------------
 Seq Scan on i200c200  (cost=0.00..233332.28 rows=9999828 width=16) (actual time=29.317..11966.291 rows=10000000 loops=1)
 Planning Time: 0.034 ms
 JIT:
   Functions: 2
   Generation Time: 1.589 ms
   Inlining: false
   Inlining Time: 0.000 ms
   Optimization: false
   Optimization Time: 9.002 ms
   Emission Time: 19.948 ms
 Execution Time: 12375.493 ms
(11 rows)

Time: 12376.281 ms (00:12.376)
SET
Time: 1.955 ms
                                                       QUERY PLAN
------------------------------------------------------------------------------------------------------------------------
 Seq Scan on i200c200  (cost=0.00..233332.28 rows=9999828 width=16) (actual time=0.063..3897.302 rows=10000000 loops=1)
 Planning Time: 0.037 ms
 Execution Time: 4292.400 ms
(3 rows)

Time: 4293.196 ms (00:04.293)

Cheers,

Jeff
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