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.
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 --------------------------------------------------
