Do you remember the task with the users import from the recipe named How to properly configure Data Import Handler? We imported all the users from our client database but it took ages – about two weeks. Our client is very happy with the results. His database is now not used for searching but only updating. And yes, that is the problem for us – how do we update data in the index? We can't fetch the whole data every time – it took two weeks. What we can do is an incremental import which will modify only the data that has changed since the last import. This task will show you how to do that.
Please refer to the How to properly configure Data Import Handler recipe in this chapter to get to know the basics of the Data Import Handler configuration. I assume that Solr is set up according to the description given in the mentioned recipe.