Andres Freund <andres(at)anarazel(dot)de> writes: > I don't quite know what the hook in $subject was originally designed > for, but right now it has the problem that it's not invoked for EXPLAIN > EXECUTE. That's because ExplainExecuteQuery directly calls > ExplainOnePlan instead of ExplainOneQuery_hook.
> Unfortunately that's not entirely trivial to fix, because the hook > accepts a Query, not a PlannedStmt.
AFAIR, the purpose of that hook was to let index advisor plugins have control of the planning step in an EXPLAIN, so that they could do things like injecting hypothetical indexes. There isn't any easy way to do something similar in EXPLAIN EXECUTE because the plan comes out of the plancache.