Subject: Re: Why HDD performance is better than SSD in this case
To: Neto pr <netopr9@gmail.com>,
 postgres performance list <pgsql-performance@postgresql.org>
References: 
 <CA+wPC0PsWacZpNX2OfRSSauUg9iNa7tReJU0oTLnM7K8PFFt6A@mail.gmail.com>
From: Mark Kirkwood <mark.kirkwood@catalyst.net.nz>
Message-ID: <4fc347b1-a7f9-c0cf-58e6-99f0c37028b2@catalyst.net.nz>
Date: Tue, 17 Jul 2018 18:07:44 +1200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101
 Thunderbird/52.9.1
MIME-Version: 1.0
In-Reply-To: 
 <CA+wPC0PsWacZpNX2OfRSSauUg9iNa7tReJU0oTLnM7K8PFFt6A@mail.gmail.com>
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Content-Language: en-US
Precedence: bulk

Can you post make and model of the SSD concerned? In general the cheaper 
consumer grade ones cannot do sustained read/writes at anything like 
their quoted max values.

regards

Mark


On 17/07/18 17:00, Neto pr 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
>