It´s a year old question...but i found something from unityjdbc.com:
They seem to have a JDBC Driver for MongoDB and Splunk: http://www.unityjdbc.com/mongojdbc/setup/mongodb_jdbc_splunk.pdf
JDBC Drive here: http://www.unityjdbc.com/mongojdbc/mongo_jdbc.php
Though i haven´t tried that yet.
I tried using this plugin to get db input into splunk.
The driver works fine when using DB Query (under Splunk DB Connect) but when trying to get data into splunk using tail method I have this problem here: http://answers.splunk.com/answers/246656/getting-mongodb-data-into-splunk-on-isodate-rising.html
Unfortunately, this is not supported via DBConnect at this time. One workaround for the time being is to do a scripted output against Python and output the results in a csv (lookup file).
If you are new to using Splunk, here's a link to how to setup a scripted input...quite easy!
To do lookups, here is a link: http://docs.splunk.com/Documentation/Splunk/5.0.3/Tutorial/Usefieldlookups
Question: what is your use case for MongoDB...very curious!
Thanks for the reply.I did a bit over the weekend. Getting closer to the goal. Will keep you posted.
Why MongoDB? Because of the unstructured format of the data which has to be plotted against multiple xml(s) and also the huge amount of data handling. Relational DBs, if used, will have the complexity of tweaking to a huge extent.