"Bryan Murphy" <bryan(dot)murphy(at)gmail(dot)com> writes:
> When we run pg_dump on our database, our web site becomes completely
> unresponsive. ...
> Does pg_dump create table locks? It doesn't look like an I/O problem
> as far as I can tell...
Only access-share locks, but that could still be an issue if anything in
your system likes to take exclusive locks. Have you looked into
pg_locks to see if anything's getting blocked?
pg_dump is entirely capable of causing an unpleasant amount of I/O
load, but that shouldn't result in "complete unresponsiveness",
and anyway your iostat output doesn't look like you're saturated...
regards, tom lane