In the last few weeks I have been having a lot of issues with connecting to databases from KNIME.
For example, if I connect to an Oracle database, I sometimes get the message:-
Could not create connection to database: Could not find driver class: oracle.jdbc.driver.T4CDriverExtension
The issue is resolved by saving the KNIME workflow, closing the KNIME application entirely and re-starting KNIME etc.
The connection always works again after this.
These issues did not occur before the most recent KNIME update - but I have no evidence that the update itself caused any issues - it may be mere coincidence.
Does anyone have any idea what may be causing this issue? I can only find resolutions for this error, relating to the absence of the driver (which certainly does not apply here).
I've been having very similar problems, ever since I've updated my Knime to 3.3.0; The driver I used for oracle stopped working entirely, and I had to download a new version, ojdbc7.jar. I get the same error message as above.
What I've noticed though, is that even if I remove the jar file from Preferences -> KNIME -> Databases, I'm still able to select oracle.jdbc.OracleDriver from the drivers list in Database Connector node.
I've tried adding new node, and filling out the config, still the same error. I've tried flushing dns, still the same error.
Is there a way to fix it, or at least troubleshoot, so that we can get to the bottom of this?
can you have a look into the KNIME log when the error occurs. To view the KNIME log open KNIME and go to View->Open KNIME log. In the KNIME log you should find several log entries regarding which driver KNIME is used etc. When KNIME starts the user defined drivers are loaded at the beginning. To find these entries search for "Load driver from file" or "Load driver from directory" in the log file. When executing a DB node KNIME is also logging which driver is used to establish the connection. To find these entries search for "Loading driver from DB factory" in the KNIME log.
I have tried to view the log when the problem occured, but it's not updating, I've just tried to run my workflow, the mysql connector worked fine, the database connector (oracle) threw this error:
ERROR Database Connector 2:1179 Execute failed: Could not create connection to database: Could not find driver class: oracle.jdbc.driver.T4CDriverExtension
But when I go to knime log, the last entry I see is from yesterday:
2017-02-05 16:14:22,754 : DEBUG : main : NodeContainerEditPart : : : GroupBy 0:1260 (EXECUTED)
Could the knime log not updating be part of the issue?
the Log file view within KNIME does not update automatically. In order to see the latest log messages you have to reopen it. You can also have a look at the log file with any other text viewer e.g. Wordpad. The location of the log file is displayed in the KNIME console at startup right below the header which contains the KNIME version. The line starts with "Log file is located at: ".
I'm afraid that didn't work. I checked the file itself, and it has stopped recording more than 20 minutes before the error occured. When I try to run any other node, nothing gets recorded in the knime log. I have to shut down knime and reopen, then it works fine.
Although, I've heard that some other people in my organisation have problems with their java application, so it may not necessarily be a problem with knime per se. And given that noone else reports this, it may be internal issue we're experiencing.