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 relation and scan-in-progress, with 
indices counting as relations. In that case, with max_connections=100, my tests 
shouldn't pin 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 the number 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


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