Further information is that th 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.
See schema of the tables used 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.
See schema of the tables used 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.
Regards
Neto
2018-05-05 8:16 GMT-07:00 Neto pr <netopr9@xxxxxxxxx>:
Dear all
Could you help me understand these two execution plans for the same
query (query 3 benchmark TPCH www.tpc.org/tpch), executed in two
different environments of Postgresql, as described below. These plans
were generated by the EXPLAIN ANALYZE command, and the time of plan 1
was 4.7 minutes and plan 2 was 2.95 minutes.
Execution Plan 1 (query execution time 4.7 minutes):
- https://explain.depesz.com/s/Ughh
- Postgresql version 10.1 (default) with index on l_shipdate (table lineitem)
Execution Plan 2 (query execution time 2.95 minutes):
- https://explain.depesz.com/s/7Zb7
- Postgresql version 9.5 (version with source code changed by me) with
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
