Re: comparison between 2 execution plans

Dear,

2018-05-05 9:57 GMT-07:00 Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>:

> On 05/05/2018 06:26 AM, Neto pr wrote:
>
>> Dear all
>>
>> Could you help me understand these two execution plans for the same query
>> (query 3 benchmark TPCH www.tpc.org/tpch <http://www.tpc.org/tpch>),
>> executed in two different environments of Postgresql, as described below:
>> Execution Plan 1:
>> - https://explain.depesz.com/s/Ughh
>> - Postgresql version 10.1 (default) with index on l_shipdate (table
>> lineitem)
>>
>> Execution Plan 2:
>> - https://explain.depesz.com/s/7Zb7
>> - Postgresql version 9.5 (version with source code changed by me) with
>>
>
> It might help if you explained what 'version with source code changed by
> me' means?
>

Postgresql with modified source code, is that I modified some internal
functions of cost (source code) and parameters in Postgresql.conf so that
it is possible for the DBMS to differentiate cost of read (random and
sequence) and write (random and sequence), this is because reading in SSDs' and
more than 400 times faster than HDD. This is due to academic research that
I am doing.

>
> Also the schema for the table lineitem from both instances might help shed
> light.
>

see schema of the tables below:
https://docs.snowflake.net/manuals/_images/sample-data-tpch-schema.png

I am using 40g scale, in this way the lineitem table has (40 * 6 million)
240 million of the rows.

> Any reason why the index changed between instances?
>
>
>
> index on l_orderkey (table lineitem).
>>
>> Some doubts
>> - Difference between GroupAggregate and Finalize GroupAggregate
>> - because some algorithms show measurements on "Disk" and others on
>> "Memory" example:
>> - External sort Disk: 52784kB
>> - quicksort Memory: 47770kB
>>
>> Because one execution plan was much smaller than the other, considering
>> that the query is the same and the data are the same.
>> --------------------------------------------------
>> select
>> l_orderkey,
>> sum(l_extendedprice * (1 - l_discount)) as revenue,
>> o_orderdate,
>> o_shippriority
>> from
>> customer,
>> orders,
>> lineitem
>> where
>> c_mktsegment = 'HOUSEHOLD'
>> and c_custkey = o_custkey
>> and l_orderkey = o_orderkey
>> and o_orderdate < date '1995-03-21'
>> and l_shipdate > date '1995-03-21'
>> group by
>> l_orderkey,
>> o_orderdate,
>> o_shippriority
>> order by
>> revenue desc,
>> o_orderdate
>> --------------------------------------------------
>>
>> best regards
>> Neto
>>
>
>
> --
> Adrian Klaver
> adrian(dot)klaver(at)aklaver(dot)com
>

Regards
Neto