Re: comparison between 2 execution plans

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?

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

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