dougwilson
commented
2 years ago Hello, and thank you for opening a new issue for this, so I can fix the error handling under that first ticket.
What's so special about Error: read ETIMEDOUT at TCP.onStreamRead that prevents the pool from reconnecting to the database?
That error is not actually produced from this library, rather it comes from Node.js. It is the representation of a TCP timeout on the system (OS) network stack. When it occurs, the TCP connection is no longer functional. You would need to create a new connection to the database. If you are using the pool, you would do this using .getConnection or use .createConnection if not using the pool.
How can I reproduce this?
Unfortunately I am not sure. It is poasible the Node.js project may know how, but I unfortunately do not.
What does this mean: Cannot enqueue Query after fatal error.? My first thought was that the fatal error was a fatal error on the connection itself, but that doesn't seem to be the case as I get a fatal error on the connection when I stop the database, but it comes back up just fine as previously described.
This means that you have a reference to a specific connection object in your code. That connection then emitted an error that had the .fatal property set to true, but then your code called .query on that same object after the error.
Ideally if you get a fatal error on a connection, you should either call .release on it to destroy it and call .getConnection to get a new one if you are using the pool, or just call .createConnection to create a new connection if not. Always be careful how you structure your logic, as when the TCP connection is lost from the server, ant temp tables, variables, and uncommitted transactions are lost.
bmaupin
I'm indirectly using this library via loopback-connector-mysql. By default, that library creates a pool with 10 connections, so any time there is a database issue, my expectation would be that once the database was reachable again, any bad connections would be terminated and the pool would be filled with good connections. This is what I've observed so far in my testing with a local database. If I stop the database, I get errors such as:
Or if I then start up a dummy server that times out connections, e.g.
(https://stackoverflow.com/a/37465639/399105)
I get errors such as:
In both cases (and others I tried), after bringing the database back up, the application was able to reconnect to it without any intervention.
However, in a production application we ran into some errors where the application was hung and would not reconnect to the database until the application was restarted:
(the last error is repeated, I'm guessing for each connection in the pool).
So I have some questions:
Error: read ETIMEDOUT at TCP.onStreamReadthat prevents the pool from reconnecting to the database?Cannot enqueue Query after fatal error.? My first thought was that the fatal error was a fatal error on the connection itself, but that doesn't seem to be the case as I get a fatal error on the connection when I stop the database, but it comes back up just fine as previously described.Thanks!