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From Ming Liu <>
Subject Re: how to read debug info after set SUBQUERY_UNNESTING to 'debug'
Date Mon, 29 Jan 2018 15:09:33 GMT
Thanks Dave and Suresh,

I was trying to understand this debug skill and try to make it a tool that can engineers can
use in the field to check query performance issues related to subquery unnestting. I think
in most cases Trafodion does very well to unnest subqueries. I am trying to find out those
scenarios that it cannot do unnesting. And hope this tool can help.

I tried this query:

explain options 'f' select * from t1 where not exists (select * from t2 where t2.a2 = t1.a1

>From some reference document, it was said EXISTS after a NOT, OR will not be unnest, but
I didn't see that behavior. Maybe Trafodion can already optimize these subqueries.

The subquery I tested is correlated, but it doesn't show any warning. I will try to use gdb
to do some debugging asap.


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