Ok, the problem was a little bit more trivial than I thought.
The issue is that under a low rate there may be no transaction in progress, however the wait procedure was relying on select's timeout. If nothing is active there is nothing to wait for, thus it was an active loop in this case...
I've introduced a usleep call in place of select for this particular case. Hopefully this is portable.
Shouldn't we use pg_usleep to ensure portability? it is defined for front-end code. But it returns void, so the error check will have to be changed.
I didn't see the problem before the commit I originally indicated , so I don't think it has to be back-patched to before v10.
