max_connections proposal

There might be a very cheap and simple way to help reduce the number of
people running into problems because they set massive max_connections
values that their server cannot cope with instead of using pooling.

In the default postgresql.conf, change:

max_connections = 100 # (change requires restart)
# Note: Increasing max_connections costs ~400 bytes of shared memory
# per connection slot, plus lock space (see max_locks_per_transaction).

to:

max_connections = 100 # (change requires restart)
# WARNING: If you're about to increase max_connections above 100, you
# should probably be using a connection pool instead. See:
# http://wiki.postgresql.org/max_connections
#
# Note: Increasing max_connections costs ~400 bytes of shared memory
# per connection slot, plus lock space (see max_locks_per_transaction).
#

... where wiki.postgresql.org/max_connections (which doesn't yet exist)
explains the throughput costs of too many backends and the advantages of
configuring a connection pool instead.

Sure, this somewhat contravenes the "users don't read - ever" principle,
but we can hope that _some_ people will read a comment immediately
beside the directive they're modifying.

--
Craig Ringer