On 2017/04/07 8:36, Tom Lane wrote: > I wrote: >> I propose to deal with this by reverting 3838074f8 in toto, and then >> trying to clarify that comment, and maybe adding a regression test case >> based on the example I showed earlier so that it will be a little more >> obvious if someone breaks this again. >> However, I see that 3838074f8 touches some partitioning code, which >> makes me wonder if there's anything in the partitioning logic that >> really depends on this erroneous "optimization".
Definitely misread the comment there, but was mystified why the tests didn't break. The partitioning tuple-routing code optionally avoids converting tuples by using this optimization. Since TupleDesc.tdtypeid of the parent and the partition to which a tuple is routed are never the same, tuples would always have to be converted before 3838074f8. One of the earlier versions of that patch introduced a consider_typeid parameter for which only ExecEvalConvertRowtype() passed true. > After further poking around, I've concluded that that approach is probably > an overreaction. Of the dozen or so callers of convert_tuples_by_position > and convert_tuples_by_name, it seems that ExecEvalConvertRowtype is the > only one that really needs the correct composite-datum headers in the > converted tuple; and even for it, forcing use of do_convert_tuple is > a pretty expensive, brute-force way to get that result. Ashutosh's > proposal to use heap_copy_tuple_as_datum when no column rearrangement > is required should be substantially more efficient. > > So I now think it's okay to remove consideration of matching the target > rowtype OID from the tupconvert.c functions, although we have to realize > that that is effectively an API change for them, one which has a definite > potential for biting third-party callers. And I see that just in 3f902354b08 lets the partition tuple-routing code keep utilizing that optimization. Thanks, Amit -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers