On Wed, Apr 13, 2016 at 2:11 PM, Robert Haas <robertmh...@gmail.com> wrote: > So, clearly that's not good. It should at least be consistent. But > more than that, the fact that postgres_fdw sets the xmax to 0xffffffff > is also pretty wacky. We might use such a value as a sentinel for > some data type, but for transaction IDs that's just some random normal > transaction ID, and it's NOT coming from t1. I haven't tracked down > where it *is* coming from yet, but can't imagine it's any place very > principled.
And, yeah, it's not very principled. rhaas=# select ft1.xmin, ft1.xmax, ft1.cmin from ft1; xmin | xmax | cmin ------+------------+------- 96 | 4294967295 | 16392 96 | 4294967295 | 16392 96 | 4294967295 | 16392 96 | 4294967295 | 16392 (4 rows) What's happening here is that heap_getattr() is being applied to a HeapTupleHeaderData which contains DatumTupleFields. So 96 is datum_len_, 4294967295 is the -1 recorded in datum_typmod, and 16392 is the compose type OID recorded in datum_typeid, which happens in this case to be the OID of ft1. Isn't that special? It's hard for me to view this as anything other than a bug in postgres_fdw - which of course means that this open item boils down to the complaint that the way system columns are handled by join pushdown isn't bug-compatible with the existing behavior.... -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers