Getting "ERROR: no unpinned buffers available" on HEAD, should I investigate?

Hi

When I run my FK concurrency test suite on an unpatched HEAD, I'm getting quite a lot of "no unpinned buffers
available"errors. 

Increasing shared_buffers from 32MB (the default) to 64MB makes the errors go away, as does setting fsync=off.

I'm not sure how many buffers a particular backend can hold at any time. I'd have though it'd be something like one per
relationand scan-in-progress, with indices counting as relations. In that case, with max_connections=100, my tests
shouldn'tpin more than a couple of hundred buffers at a time. That, however, amounts to about 1MB or so of pinned
buffers,so it shouldn't break with shared_buffers=32MB. 

I'm also confused by fsync=off making a difference. That should make writing dirty buffers slower, but would it affect
thenumber of buffers pinned? 

In short, I'm wondering whether I might have hit a bug, or if I should just increase shared_buffers and move on.

best regards,
Florian Pflug