IllegalStateException: additional jar file '<install-path>/cache/dfscache/<id>-sqljdbc4.jar does not exist

Problem Statement

The database driver is missing from cache. This has happen on several occasions and the last time we put the jar files in the custom-jars directory and that was suppose to resolve the issue. 

Error message

Troubleshooting steps 

- log into Datameer
- adjust the URL to reflect <datameer-server>:<port>/dev
- locate and select "Cache monitor" from the "Reports" near the bottom
- listed under "Configuration" you should see a "Max Elements" with a value
- further down you'll see "Elements in cache"
- check that your "Elements in cache" is not maxed out based on the value associated with "Max Elements"
- navigate to "Evict expired elements from cache"

Cause

It appears that the dfscache did get full locally and this caused items to get pushed out.

To work-around this issue, we'd like to recommend adding the jdbc-jar files into the install-path/etc/custom-jars directory in Datameer. This will be a permanent storage for these jar files rather than a local cache.

The cache is susceptible to getting full and purging elements. The fact that the element is not restored does seem like a Datameer bug which we will investigate in further detail. The cache should be repopulated with the files that are needed.