Ref T11672. At low loads, this causes us to use more connections, which is pushing some installs over the default limits.

Rather than trying to walk users through changing max_connections, open_files_limit, fs.file-max, ulimit, etc., just put things back for now. After T11044 we should have headroom to use persistent connections within the default limits on all reasonable systems..

Loaded Phabricator, poked around.