The Bachelor course on Information Retrieval here at VU is about the theory and principles behind search engines: How can we search huge collections of unstructured text data in an efficient and accurate manner? But apart from these theoretical considerations, it is also important to look at actual implementations and products, to understand how the theory translates to practical applications. Solr and Elasticsearch are currently the most popular search engine implementations, but only the latter shows a steep upward trend. And as it happens, the company behind Elasticsearch — called Elastic — is headquartered in Amsterdam! So it seemed only natural that the students of this Information Retrieval course should learn something about Elasticsearch. Elastic agreed without hesitation to provide a guest lecture, which was given by Boaz Leskes on Wednesday this week. He explained the different stages that a document goes through when it enters Elasticsearch and how it can later be retrieved when queries are executed, all in a scalable, robust, and (near-)real-time manner. The presentation was really nice and we all learned lots of interesting things about Elasticsearch and modern search engines in general. The slides can be found here, and we are of course very happy that this event was seen as a success from Elastic’s side as well, as you can read in their blog post. So, I would like to thank the people at Elastic to make this possible, and I hope we can do it again!