> Great to read from someone who knows it so deeply.

I'd say it's a decent read on Elasticsearch tuning at the intermediate level, but not enough to really get high performance from Elastic.

One of the problems with Elastic tuning is that the tuning parameters depend deeply on the type of data you're indexing. Indexing text is far different than indexing numbers or dates. A mapping with a large number of fields will behave differently than with just a few. Some datasets can easily be split up into different indexes, and others are cannot be.

To really get the most from Elasticsearch, you have to know what it's doing under-the-hood, and how that maps on to your data. Elasticsearch hides so much complexity (generally a good thing), but unfortunately, it can be difficult to know where the bottlenecks are.