Re: pgsql: Add the "snapshot too old" feature

Kevin,

This commit makes me very uneasy.  I didn't much care about this patch mainly because I didn't imagine its consequences. Now, I see following:

1) We uglify buffer manager interface a lot.  This patch adds 3 more arguments to BufferGetPage().  It looks weird.  Should we try to find less invasive way for doing this?

2) Did you ever try to examine performance regression?  I tried simple read only test on 4x18 Intel server.

pgbench -s 1000 -c 140 -j 100 -M prepared -S -T 300 -P 1 postgres (data fits to shared_buffers)

So, for read-only benchmark this patch introduces more than 5 times regression on big machine.