Re: checkpointer continuous flushing - V18

>> Random updates on 16 tables which total to 1.1GB of data, so this is in
>> buffer, no significant "read" traffic.
>>
>> (1) with 16 tablespaces (1 per table) on 1 disk : 680.0 tps
>> per second avg, stddev [ min q1 median d3 max ] <=300tps
>> 679.6 ± 750.4 [0.0, 317.0, 371.0, 438.5, 2724.0] 19.5%
>>
>> (2) with 1 tablespace on 1 disk : 956.0 tps
>> per second avg, stddev [ min q1 median d3 max ] <=300tps
>> 956.2 ± 796.5 [3.0, 488.0, 583.0, 742.0, 2774.0] 2.1%
>
> Interesting. That doesn't reflect my own tests, even on rotating media,
> at all. I wonder if it's related to:
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=23d0127096cb91cb6d354bdc71bd88a7bae3a1d5
>
> If you use your 12.04 kernel, that'd not be fixed. Which might be a
> reason to do it as you suggest.
>
> Could you share the exact details of that workload?

See attached scripts (sh to create the 16 tables in the default or 16
table spaces, small sql bench script, stat computation script).

The per-second stats were computed with:

grep progress: pgbench.out | cut -d' ' -f4 | avg.py --length=1000 --limit=300

Host is 8 cpu 16 GB, 2 HDD in RAID 1.

--
Fabien.