PM2 Error: Connection lost: The server closed the

Question

PM2半夜莫名重启，然后报下面的错是什么意思？是mysql的原因？

Error: Connection lost: The server closed the connection.

    at Protocol.end (/xxxx/xxx/xxx/node_modules/mysql/lib/protocol/Protocol.js:113:13)

    at Socket.<anonymous> (/xxxx/xxx/xxx/node_modules/mysql/lib/Connection.js:109:28)

    at emitNone (events.js:111:20)

    at Socket.emit (events.js:208:7)

    at endReadableNT (_stream_readable.js:1056:12)

    at _combinedTickCallback (internal/process/next_tick.js:138:11)

    at process._tickDomainCallback (internal/process/next_tick.js:218:9)

Node.js的版本是v8.9.0. PM2的版本是2.9.1. mysql库的版本是2.15.0。