On 2019-Jan-07, Nikolay Shaplov wrote: > Asserts are cool thing. I found some unexpected stuff. > > parallel_workers option is claimed to be heap-only option. > > But in src/backend/optimizer/util/plancat.c in get_relation_info > RelationGetParallelWorkers is being called for both heap and toast tables > (and > not only for them).
Ugh. I wonder if it makes sense for a toast table to have parallel_workers. I suppose it's not useful, since a toast table is not supposed to be scanned in bulk, only accessed through the tuptoaster interface. But on the other hand, you *can* do "select * from pg_toast_NNN", and it almost all respects a toast table is just like a regular heap table. > Because usually there are no reloptions for toast, it returns default -1 > value. If some reloptions were set for toast table, > RelationGetParallelWorkers > will return a value from uninitialized memory. Well, if it returns a negative number or zero, the rest of the server should behave identically to it returning the -1 that was intended. And if it returns a positive number, the worst that will happen is that a Path structure somewhere will have a positive number of workers, but since queries on toast tables are not planned in the regular way, most likely those Paths will never exist anyway. So while I agree that this is a bug, it seems pretty benign. Unless I overlook something. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
