MySQL giving “read ECONNRESET” error after idle time on node.js server

Question

I'm running a Node server connecting to MySQL via the node-mysql module. Connecting to and querying MySQL works great initially without any errors, however, the first query after leaving the Node server idle for a couple hours results in an error. The error is the familiar read ECONNRESET, coming from the depths of the node-mysql module.

A stack trace (note that the three entries of the trace belong to my app's error reporting code):

Error
at exports.Error.utils.createClass.init (D:\home\site\wwwroot\errors.js:180:16)
at new newclass (D:\home\site\wwwroot\utils.js:68:14)
at Query._callback (D:\home\site\wwwroot\db.js:281:21)
at Query.Sequence.end (D:\home\site\wwwroot\node_modules\mysql\lib\protocol\sequences\Sequence.js:78:24)
at Protocol.handleNetworkError (D:\home\site\wwwroot\node_modules\mysql\lib\protocol\Protocol.js:271:14)
at PoolConnection.Connection._handleNetworkError (D:\home\site\wwwroot\node_modules\mysql\lib\Connection.js:269:18)
at Socket.EventEmitter.emit (events.js:95:17)
at net.js:441:14
at process._tickCallback (node.js:415:13)

This error happens both on my cloud Node server and MySQL server as well as a local setup of both.

My questions:

1. Does this problem appear to be a disconnection of Node's connection to my MySQL server(s), perhaps due to a connection lifetime limitation?

2. When using connection pools, node-mysql is supposed to gracefully handle disconnections and prune them from the pool. Is it not aware of the disconnect until I make a query, thus making the error unavoidable?

3. Considering that I see the "read ECONNRESET" error a lot in other StackOverflow posts, should I be looking elsewhere from MySQL to diagnose the problem?

Update: After more browsing, I think my issue is a duplicate of this one. It appears his connection is disconnecting as well, but no one has suggested how to keep the connection alive or how to address the error outside of failing on the first query back.

Answer 1

I reached out to the node-mysql folks on their Github page and got some firm answers.

1. MySQL does indeed prune idle connections. There's a MySQL variable "wait_timeout" that sets the number of second before timeout and the default is 8 hours. We can set the default to be much larger than that. Use show variables like 'wait_timeout'; to view your timeout setting and set wait_timeout=28800; to change it.

2. According to this issue, node-mysql doesn't prune pool connections after these sorts of disconnections. The module developers recommended using a heartbeat to keep the connection alive such as calling SELECT 1; on an interval. They also recommended using the node-pool module and its idleTimeoutMillis option to automatically prune idle connections.

Answer 2

If this happens when establishing a single reused connection, it can be avoided by establishing a connection pool instead.

For example, if you're doing something like this...

var db = require('mysql')
  .createConnection({...})
  .connect(function(err){});

do this instead...

var db = require('mysql')
  .createPool({...});

Answer 3

Does this problem appear to be a disconnection of Node's connection to my MySQL server(s), perhaps due to a connection lifetime limitation?

Yes. The server has closed its end of the connection.

When using connection pools, node-mysql is supposed to gracefully handle disconnections and prune them from the pool. Is it not aware of the disconnect until I make a query, thus making the error unavoidable?

Correct, but it should handle the error internally, not pass it back to you. This appears to be a bug in node-mysql. Report it.

Considering that I see the "read ECONNRESET" error a lot in other StackOverflow posts, should I be looking elsewhere from MySQL to diagnose the problem?

It is either a bug in the node-MySQL connection pool implementation, o else you haven't configured it properly to detect failures.