There appears to be a connection ticket leak in OurListener constructor (db.cpp) when a boost thread can't be created. The listener successfuly acquires a ticket from the TicketHolder and then relies on connThread method's TicketHolderReleaser to actually release the ticket when the thread finishes. But when the thread can't be created, the ticket is never released and a connection slot is left "used" forever. The fix should be a trivial call to connTicketHolder.release() when an exception ocurrs in OurListener constructor after the connection ticket has been acquired.