Danno / Dannotate Troubleshooting

This section gives some hints on troubleshooting problems with Danno and Dannotate.

Java Exceptions

The following exceptions may be logged in the Danno.log file, or elsewhere depending on the circumstances

Failed to lock database after N attempts

This happens with an Jena/RDB triple store when something (e.g. the Danno servlets, admin tools or unit tests) attempts to gain an exclusive lock on the triple store's SQL database and fails.

  1. See if anything else may be accessing the triple store, shut down the offending application(s) and repeating the action that failed.
  2. It is possible that there is a stale lock on the triple store database. In the case of MySQL, look for a table called "jena_mutex" in the database. If you find the table, DROP it and repeat the operation.