I've read the code and now I have more suggestions.
1. Easy one. The case of different natts of expected and acutal result throws same errmsg as the case of wrong types. I think we should assist the user more here
if (natts != tupdesc->natts) ereport(ERROR, (errcode(ERRCODE_DATATYPE_MISMATCH), errmsg("remote query result rowtype does not match the specified FROM clause rowtype")));
and here
if (type_id != tupdesc->attrs[i]->atttypid) ereport(ERROR, (errcode(ERRCODE_DATATYPE_MISMATCH), errmsg("remote query result rowtype does not match the specified FROM clause rowtype")));
2. This code errhint("You may need to increase max_worker_processes.") Is technically hinting absolutley right. But this extension requires something like pg_bouncer or what is called "thread pool". You just cannot safely fire a background task because you do not know how many workes can be spawned. Maybe it'd be better to create 'pool' of workers and form a queue of queries for them? This will make possible start a millions of subtasks.
This is not easy, because pgworker is related to database, not to server. There are servers where you can have thousands databases.
Regards
Pavel
3. About getting it to the core, not as an extension. IMO this is too sharp thing to place it into core, I think that it's best place is in contribs.
Thanks for the work on such a cool and fun extension.
