Re: Why HDD performance is better than SSD in this case

Can you show the configuration of postgresql.conf?
Query configuration method:
Select name, setting from pg_settings where name ~ 'buffers|cpu|^enable';

On 2018年07月17日 13:17, Benjamin Scherrey wrote:
> What's the on disk cache size for each drive? The better HDD
> performance problem won't be sustained with large amounts of data and
> several different queries.
>
>   - - Ben Scherrey
>
> On Tue, Jul 17, 2018, 12:01 PM Neto pr <netopr9(at)gmail(dot)com
> <mailto:netopr9(at)gmail(dot)com>> wrote:
>
> Dear,
> Some of you can help me understand this.
>
> This query plan is executed in the query below (query 9 of TPC-H
> Benchmark, with scale 40, database with approximately 40 gb).
>
> The experiment consisted of running the query on a HDD (Raid zero).
> Then the same query is executed on an SSD (Raid Zero).
>
> Why did the HDD (7200 rpm)  perform better?
> HDD - TIME 9 MINUTES
> SSD - TIME 15 MINUTES
>
> As far as I know, the SSD has a reading that is 300 times faster
> than SSD.
>
> --- Execution  Plans---
> ssd 40g
> https://explain.depesz.com/s/rHkh
>
> hdd 40g
> https://explain.depesz.com/s/l4sq
>
> Query ------------------------------------
>
> select
>     nation,
>     o_year,
>     sum(amount) as sum_profit
> from
>     (
>         select
>             n_name as nation,
>             extract(year from o_orderdate) as o_year,
>             l_extendedprice * (1 - l_discount) - ps_supplycost *
> l_quantity as amount
>         from
>             part,
>             supplier,
>             lineitem,
>             partsupp,
>             orders,
>             nation
>         where
>             s_suppkey = l_suppkey
>             and ps_suppkey = l_suppkey
>             and ps_partkey = l_partkey
>             and p_partkey = l_partkey
>             and o_orderkey = l_orderkey
>             and s_nationkey = n_nationkey
>             and p_name like '%orchid%'
>     ) as profit
> group by
>     nation,
>     o_year
> order by
>     nation,
>     o_year desc
>

--
<b>张文升</b> winston<br />
PostgreSQL DBA<br />