The talk was given by Martin from the Bulgaria jug and focused on the internals of ElasticSearch, as well as its architecture. Martin discussed the ElasticSearch stack, including components like Kibana and Logstash, and highlighted the benefits of using ElasticSearch over relational databases. He explained the ElasticSearch data structure, the inverted index, and the usage of primary and replica shards for high availability and search performance. Martin also explored the code structure of ElasticSearch and demonstrated how to build a simple ElasticSearch plugin. The talk provided valuable insights for developers and users of ElasticSearch, giving them a deeper understanding of its inner workings and how to leverage its capabilities.