Antonin Houska <a...@cybertec.at> wrote: > I spent some time thinking about a special case of evaluation of the row > filter and wrote a comment that might be useful (see the attachment). However > now I think that it's not perfect if the code really relies on the fact that > value of an indexed column cannot be TOASTed due to size restrictions. > > I could hit two different error messages when trying activate TOAST on an > index column (in this case PG was build with 16kB pages), but still I think > the code is unnecessarily fragile if it relies on such errors: > > > ERROR: index row requires 8224 bytes, maximum size is 8191 > > ERROR: index row size 8048 exceeds btree version 4 maximum 5432 for index > "b_pkey" > DETAIL: Index row references tuple (0,3) in relation "b". > HINT: Values larger than 1/3 of a buffer page cannot be indexed. > > > Note that at least in ExtractReplicaIdentity() we do expect that an indexed > column value can be TOASTed. > > /* > * If the tuple, which by here only contains indexed columns, still has > * toasted columns, force them to be inlined. This is somewhat unlikely > * since there's limits on the size of indexed columns, so we don't > * duplicate toast_flatten_tuple()s functionality in the above loop over > * the indexed columns, even if it would be more efficient. > */ > if (HeapTupleHasExternal(key_tuple)) > { > HeapTuple oldtup = key_tuple; > > key_tuple = toast_flatten_tuple(oldtup, desc); > heap_freetuple(oldtup); > } > > Do I miss anything?
Well, I see now that the point might be that, in heap_update(), "id_has_external" would be true the indexed value could be TOASTed, so that the (flattened) old tuple would be WAL logged: old_key_tuple = ExtractReplicaIdentity(relation, &oldtup, bms_overlap(modified_attrs, id_attrs) || id_has_external, &old_key_copied); Nevertheless, a comment in pgoutput_row_filter(), saying that TOASTed values are not expected if old_slot is NULL, might be useful. -- Antonin Houska Web: https://www.cybertec-postgresql.com