A great tool in the SQL Server space that helps with this kind of stuff is SentryOne's plan explorer - https://www.sentryone.com/plan-explorer

No affiliation, just used it for years and loved how it works, especially when comparing cardinality estimations to actuals, index designs, and general performance characteristics.

Tanel is a well known expert/authority in Oracle circles. He co-founded Gluent ( https://gluent.com/ ), which is helping to reinvent ETL/data warehousing. See https://gluent.com/products/gluent-data-platform/

I'm a big fan of this one: http://tatiyants.com/pev/#/about

Yup it looks cool - I actually mentioned it in my post too with a screenshot.

Is there something similar for DB2?

I only applied this on Oracle, not too familiar with with DB2, but as long as DB2 has a (text) tool that reports exec plan node level metrics, this can be converted into a flame chart.

what Oracle client is being used in the screenshot of an Oracle Explain Plan?

Hi, it's using Oracle's default client sqlplus for extracting data and spool it in flamegraph.pl-friendly format to disk. And then the script runs flamegraph.pl to turn this data into a .svg chart and opens it with your default browser.