I have a "Connection lost: The server closed the connection." error, please help!

[DmitriySheludko]

Hello!

I have an application that use ActionHeroJS + ah-sequelize-plugin + Sequelize ORM + node-mysql.

Sometimes, in realy random times, i see this error:

{"level":"error","message":"! uncaught error from task: Cannot read property 'class' of null on queue default","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"! Error: Connection lost: The server closed the connection.","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"!     at Protocol.end (/var/soft/kidguard-api/node_modules/mysql/lib/protocol/Protocol.js:103:13)","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"!     at Socket.<anonymous> (/var/soft/kidguard-api/node_modules/mysql/lib/Connection.js:88:28)","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"!     at Socket.emit (events.js:117:20)","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"!     at _stream_readable.js:929:16","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"!     at process._tickDomainCallback (node.js:463:13)","timestamp":"2014-08-28T00:29:28.572Z"}
{"level":"error","message":"*","timestamp":"2014-08-28T00:29:28.572Z"}

And after this error my system stops sending requests to mysql at all. If i request any method that uses mysql - request freezes.

Please help to fix this!

[dougwilson]

Hi! Your server closed the connection on you for whatever reason. It may be because you kept the connection open too long. Please make sure you are using our pool (https://github.com/felixge/node-mysql#pooling-connections) and not keeping a single long-lived connection open for all your requests.

[DmitriySheludko]

I use pools. I have 50 connections in the pool with same result... I tryed various params but still nothing.

[DmitriySheludko]

Here is my current conf

      "database"    : "database",
      "dialect"     : "mysql",
      "port"        : 3306,
      "host"        : "127.0.0.1", 
      "username"    : "database", 
      "password"    : "database",
      "native"      : true,
      "pool"        : { maxConnections: 50, maxIdleTime: 30},

[dougwilson]

I'm not sure, and with you going though all those layers (like sequelize, etc.), I have no idea if one of those things are contributing to your issue. If you can show the code that only uses this library that creates the issue, I can certainly help.

But really, the error you posted above was Connection lost: The server closed the connection. which means your MySQL server closed the connection on you. This can of course happen (though of course I cannot tell you why the server you are using closed the connection), but should not cause:

And after this error my system stops sending requests to mysql at all. If i request any method that uses mysql - request freezes.

The request freezing could be an issue with sequelize or something, I'm not sure. Can you try only using this library and not the others to see if the issue remains? I have no idea how ActionHeroJS, ah-sequelize-plugin, or sequelize works or what they are doing. And of course if you are going through all those abstractions, you cannot know that those libraries are not what is causing your requests to "freeze" after the error. If you were using the pool from this module directly correctly, then that error would at most cause an error on a single request, but not freeze all further requests.

[cusspvz]

@DmitriySheludko this error is currently being handled at sequelize/sequelize#2448

[cusspvz]

@dougwilson i have been testing my PR sequelize/sequelize#2450 for a while before it gets merged.

It seems that, even with error event listening, this error is getting throwed away as an uncaught error.
I don't have sure why, since i'm not familiarized with node-mysql at all, could you explain me why on https://github.com/felixge/node-mysql/blob/master/lib/protocol/sequences/Sequence.js#L43 the listening count of error event should be greater than one?

[dougwilson]

That check doesn't cause anything to throw; it is used to determine where to send the error that occurred. If you called query like

conn.query('blah', callback)

That test well send it to the callback, otherwise if you did

var query = conn.query('blah')
query.on('error', onerror)
query.on('result', onresult)

the error from that query will go to the onerror function. This is the case when the listening count would be greater than one.

if you made a query and did neither of those two, the error would eventually be emitted on conn.

If you can point to the code in MySQL that is throwing the uncaught exception, I can take a look, otherwise you can always provide me a test case that does not use sequelize that throws an uncaught exception and I can point where your missing error handling is.

[DoctorDimon]

I have found, that if some mysql query completes with an error (with fatal error from DB), this query freezes 1 connection from a pool. So if I have 50 connections in a pool, system will work upon 50 fatal errors have been appeared.

So in my case, I refactor my code to prevent any error from DB, like DUPLACATE ENTRY and so on. For now I have no errors with DB and I have no problems with connection pool.

[dougwilson]

@DoctorDimon your issue doesn't sound related to what is being talked about here?

[cusspvz]

That check doesn't cause anything to throw;

Sorry for my verboseless...

Sequence.prototype.hasErrorHandler is called in-stack of protocol fatal ending described by OP by shouldErrorBubbleUp.

For some reason, the error that the OP is describing is being throwed away even with a listener on connection.error, i need to understand why this is happening so i can complete Sequelize's PR sequelize/sequelize#2450 related to OP's problem.

[dougwilson]

@cusspvz I'm saying I really cannot answer that question without some code I can run so I can point to where the error handling is missing is all. The posted code should only use this library, please, and cause an error to be thrown.

[cusspvz]

To continue my research to understand the real problem, i just need some explanation why Sequence.prototype.hasErrorHandler is looking for more than one error event listeners. :)

[DoctorDimon]

@dougwilson I was talking about issue that I had wrote when I opened this ticket. I wrote about how I had fixed it, without actually fixing an error itself. Sorry if it was offtopic.

[cusspvz]

@DoctorDimon , the OP of this issue is @DmitriySheludko , maybe you are confusing with another issue?