修复first_or_initialize / first_or_create比赛

Question

基本上我发现所有“first_or_initialize”/“first_or_create”调用都有竞争条件。

正常情况：

server1: first_or_initialize -> initialize
server1: save new record
server2: first_or_initialize -> first
server2: update old record

种族案例：

server1: first_or_initialize -> initialize
server2: first_or_initialize -> initialize
server1: save new record
server2: save new record **ERROR:  duplicate key violates unique constraint**

我该如何解决？