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:
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 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
