On Wed, Jun 1, 2022 at 11:09 PM KAWAMOTO Masaya <kawam...@sraoss.co.jp> wrote: > That sounds a nice idea. But I don't think that postgres shows in the > EXPLAIN output why the plan is selected. Would it be appropriate to > show that GEQO is used in EXPLAIN output?
I'm reminded of Greenplum's "Optimizer" line in its EXPLAIN output [1], so from that perspective I think it's intuitive. > As a test, I created a patch that add information about GEQO to > EXPLAIN output by the GEQO option. The output example is as follows. > What do you think about the location and content of information about GEQO? I am a little surprised to see GeqoDetails being printed for a plan that didn't use GEQO, but again that's probably because I'm used to GPDB's Optimizer output. And I don't have a lot of personal experience using alternative optimizers. One way to think about it might be, if we had ten alternatives, would we want a line for each showing why it wasn't selected, or just one line showing the optimizer that was selected? The latter is more compact but doesn't help you debug why something else wasn't chosen, I suppose... --Jacob [1] https://docs.vmware.com/en/VMware-Tanzu-Greenplum/6/greenplum-database/GUID-ref_guide-sql_commands-EXPLAIN.html#examples-4
