Database Reader error

  In my Knime workflow I have used a Database Reader node to fetch data from a MySQL database. I have written SQL query to select the required data. But the node fails execution with below error message

"Database Reader 266:373:368 - ERROR: Execute failed: Error writing file '/tmp/MYv30nfW' (Errcode: 28)"

 What is the reason for this error? Why is a file being created?

That error is very likely generated by MySQL database driver which is trying to write a file to the tmp folder (probably to cache some of the data). Did you check the target drive? Is there enough space on it? Does the  KNIME process have the necessary authorization to write to your tmp folder?