On Sat, May 11, 2024 at 4:12 PM Peter Geoghegan <p...@bowt.ie> wrote: > The dependency is fairly simple. In the presence of multiple arrays on > the same column, which must be contradictory/redundant, but cannot be > simplified solely due to lack of suitable cross-type support, we have > multiple arrays on the same index column. _bt_advance_array_keys wants > to deal with this by assuming that the scan key order matches the > array key order. After all, there is no indirection to disambiguate > which array belongs to which scan key.
Minor correction: there is an indirection. We can get from any BTArrayKeyInfo entry to its so->arrayData[] scan key using the BTArrayKeyInfo.scan_key offset. It'd just be inconvenient to do it that way around within _bt_advance_array_keys, since _bt_advance_array_keys's loop iterates through so->arrayData[] in the usual order (just like in _bt_check_compare). There is an assertion within _bt_advance_array_keys (and a couple of other similar assertions elsewhere) that verify that everybody got it right, though. The "Assert(array->scan_key == ikey);" assertion. So if _bt_preprocess_keys ever violated the expectations held by _bt_advance_array_keys, the problem would probably be detected before long. -- Peter Geoghegan
