support for PARALLEL SAFE #32
Description
Would it make sense to add PARALLEL SAFE to the SQL definitions for the q3c functions?
The Postgresql Documentation states:
Functions should be labeled parallel unsafe if they modify any database state, or if they make changes to the transaction such as using sub-transactions, or if they access sequences or attempt to make persistent changes to settings (e.g., setval). They should be labeled as parallel restricted if they access temporary tables, client connection state, cursors, prepared statements, or miscellaneous backend-local state which the system cannot synchronize in parallel mode (e.g., setseed cannot be executed other than by the group leader because a change made by another process would not be reflected in the leader). In general, if a function is labeled as being safe when it is restricted or unsafe, or if it is labeled as being restricted when it is in fact unsafe, it may throw errors or produce wrong answers when used in a parallel query. C-language functions could in theory exhibit totally undefined behavior if mislabeled, since there is no way for the system to protect itself against arbitrary C code, but in most likely cases the result will be no worse than for any other function. If in doubt, functions should be labeled as UNSAFE, which is the default.
From my admittedly limited understanding of the guts of q3c, it doesn't try to do anything that would prevent it from being PARALLEL SAFE, so is this a feasible change?