Hi,
Etsuro's patch is also showing the correct output for "set enable_nestloop=off". Looks good to me for back branches due to backport issues.
But below are a few observations for the same:-
1) I looked into the query plan for both "set enable_nestloop" on & off case and observe that they are the same. That is, what we see with "set enable_nestloop=on".
2) In back branches for "set enable_nestloop" on & off value, at least this type of query execution won't make any difference. No comparison of plans to be selected based on total cost of two plans old (Nested Loop with Foreign Scans) & new (Only Foreign Scan) will be done, because we are avoiding the call to "postgresGetForeignJoinPaths()" up front when we have pseudo constants.
Regards,
Nishant.
If the patch is intended for HEAD only, I also think it goes in the
right direction. But if it is intended for back branches as well, I
do not think so, because it would cause ABI breakage due to changes
made to the ForeignPath struct and the create_foreign_join_path() API.
(For the former, I think we could avoid doing so by adding the new
member at the end of the struct, not in the middle, though.)
Thanks for pointing this out. You're right. The patch has backport
issue because of the ABI breakage. So it can only be applied on HEAD.
To avoid this issue, I am wondering if we should modify
add_paths_to_joinrel() in back branches so that it just disallows the
FDW to consider pushing down joins when the restrictlist has
pseudoconstant clauses. Attached is a patch for that.
I think we can do that in back branches. But I'm a little concerned
that we'd miss a better plan if FDW cannot push down joins in such
cases. I may be worrying over nothing though if it's not common that
the restrictlist has pseudoconstant clauses.
Thanks
Richard