By some lakhs, I assume you mean 100,000s of DITA files.
We have achieved this in one of our solutions but beware that if you are using Windchill, you can have problems if you have a large amount of images (say more than 20GB). In that case you will want to ensure your server has sufficient disk space for the cache vault and also look into file vaulting instead of storing all content in the database.
To your original question, the fastest way to check in that many files is to build temporary DITA maps to hold references to each of the files. You can build those DITA maps via some sort of scripts or perhaps in Java DOM. Then you will check in each DITA map one after the other. Finally you will remove all DITA maps from the Windchill server and the DITA topics themselves will remain.
We found that only a few thousand DITA topics could be linked into a DITA map successfully, so you will need many DITA maps. Perhaps you can have up to 10,000 DITA topics in a map? You will need to test on your system to see what works best.
Hope that helps.
-Gareth
