"Jeroen T. Vermeulen" <jtv(at)xs4all(dot)nl> writes:
> Now if I understood a bit more of what's going on here, at least I could
> document it...
Well, you could dig through backend/executor/node*.c and see which of
the node types pay attention to es_direction. To a first approximation
it looks like these do:
Functionscan
Append
Indexscan
Mergejoin
Limit
Material
Subqueryscan
Seqscan
Sort
Tidscan
although I have not thought about which other upper plan nodes might be
okay (ie, they're safe if their input nodes are). Also, a Material or
Sort node will hide any direction-unsafety in its input.
regards, tom lane