Re: [HACKERS] asynchronous execution

Hello,

At Fri, 20 Oct 2017 17:37:07 +0900 (Tokyo Standard Time), Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> wrote in <20171020(dot)173707(dot)12913619(dot)horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>
> The attached PoC patch theoretically has no impact on the normal
> code paths and just brings gain in async cases.

The parallel append just committed hit this and the attached are
the rebased version to the current HEAD. The result of a concise
performance test follows.

patched(ms) unpatched(ms) gain(%)
A: simple table scan : 3562.32 3444.81 -3.4
B: local partitioning : 1451.25 1604.38 9.5
C: single remote table : 8818.92 9297.76 5.1
D: sharding (single con) : 5966.14 6646.73 10.2
E: sharding (multi con) : 1802.25 6515.49 72.3

> A and B are degradation checks, which are expected to show no
> degradation. C is the gain only by postgres_fdw's command
> presending on a remote table. D is the gain of sharding on a
> connection. The number of partitions/shards is 4. E is the gain
> using dedicate connection per shard.

Test A is accelerated by parallel sequential scan. Introducing
parallel append accelerates test B. Comparing A and B, I doubt
that degradation is stably measurable at least my environment but
I believe that there's no degradation theoreticaly. The test C to
E still shows apparent gain.
regards,

--
Kyotaro Horiguchi
NTT Open Source Software Center