[solved] MySQL Connector not working with update to 3.7.1

I just updated and when running an existing workflow that worked find this morning it now errors. I’ve tried different configurations - with workflow credentials and with manual input - and, of course, verified that the database is reachable via a sql client with the same credentials.

The error message is Execute failed: Could not create connection to database: Host is down (connect failed)

Can anyone help me find a fix? Is it me or is there a problem with the update?


I have 3.7.1 and old workflows with MySQL connector work just fine. Looks like a problem at the server side.


Hi @mtshaw -

What node are you using for the connection? Can provide a bit more information about the configuration you’re using, and any log messages you might be seeing?

I’m not sure offhand what might be wrong, but an easy thing to try might be the new DB nodes. You can download them as part of the KNIME Database (Preview) extension - they’ll be located under KNIME Labs in the repository.

Hi @evert.homan, I think the issue is something else. My colleague can run the same workflow with the same configuration and it works perfectly as it always used to on my machine. So I doubt it’s server-related. He’s using an older version of Knime (3.7.0). My next step will be to revert, installing an older version of Knime, to see if it is related to the update.

Hi @ScottF, I tried the new node – thanks for the heads up on the change, by the way – but without any success.

The error code is different: “ERROR MySQL Connector (Labs) 3:930:964 Execute failed: DB Session [long id number] is invalid. Communications link failure” - note that I removed session id number.

I’m beginning to wonder if the problem is with the MySQL driver - that that was somehow corrupted separately but at the same time as the Knime update. Next step I’ll take is to reinstall Knime 3.7.0 and see if it works.

As an update here @evert.homan and @ScottF:
I did a clean install of Knime 3.7.0 on my machine and ran the same, unaltered workflow from the same local directory, without reconfiguring it, and it worked fine.

It was specifically the database readers that were not working in my version of 3.7.1. The workflow in question used the MySQL connector node but both the new labs version of that node and the generic DB connector also didn’t work. I’m not sure why the installation of 3.7.1 affected these nodes on my computer but it appears to have done so. For now I’ll use 3.7.0 but I realise that isn’t a long-term solution and any further suggestions for trouble shooting would be welcome.

Nothing changed in the code or with drivers from 3.7.0 to 3.7.1. I confirmed this in the changelog, but also consulting the lead engineer over the database frameworks. The current database nodes are in maintenance mode essentially, and the new DB nodes are the only ones being actively developed on. Once they are GA (later this year) we will provide a migration utility to convert workflows over.

That doesn’t help today, but wanted to get that info out there because I believe either this is an environment issue or perhaps a corrupted install.

Few things to try

  1. Add the “-clean” flag to your knime.ini file to clean up the eclipse environment. Just add it right before the “-vmargs” argument.
  2. When you mentioned using another client/tool to connect, was this a JDBC tool or the mysql client tools?
  3. Check the OS’s firewall or Antivirus to see if the connection is getting blocked. The is fairly common on Windows.
  4. Download and install a fresh 3.7.1 instance when you have time, and see if that works.

The fact that one instance works and another doesn’t makes me think it’s that instance. Although rare, I have run into cases where an upgrade seemed to finish successfully, but was corrupted for some reason. In those case I suggest backing your workflow repository up, saving your knime.ini file, and setting up a new instance. I would suggest running through a few of the steps above first, reinstall is always my last suggestion.



Hi @jeffgullick-knime, thanks for the timely help and for filling us in on the coming changes to the DB connectors.

I tried your suggestions in order and to my chagrin it was my computer’s network filtering (your point 3.) that proved the problem. A green flag to all traffic originating from and to Knime means it now works, though I’m still not sure what my computer was permitting in the old and the fresh installation of 3.7.0 and was blocking in my installation 3.7.1 or why this was never an issue with another update (I’ve used Knime for years.) I’m relieved to have it all working and to know that it won’t be an issue going forward.

Thanks for your help!


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