Dear,
2018-05-05 9:57 GMT-07:00 Adrian Klaver <adrian.klaver@xxxxxxxxxxx>:
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.
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
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.klaver@xxxxxxxxxxx
Regards
Neto
