This list is a compilation of readings which are valuable to a general understanding of the operation of Cockroach. This list is extensive (but not exhaustive), don't feel you need to read everything here, it's provided as a way to drill down into topics you find interesting, if you so choose. The entries in each section are roughly organized in recommended order of consumption, but this is not a strict ordering in any sense.
...
Enlightening the I/O Path: A Holistic Approach for Application Performance
Admission control and scheduling of remote processes in loosely-coupled distributed systems
Regulating I/O Performance of Shared Storage with a Control Theoretic Approach
...
Basics of SQL indexing, independent of database: https://use-the-index-luke.com/
Index Selection in CockroachDB: https://www.cockroachlabs.com/blog/index-selection-cockroachdb-2/
Not especially specific to Cockroach - great as an introduction to index selection
SQL Query Planning: https://github.com/cockroachdb/cockroach/blob/master/docs/RFCS/20171213_sql_query_planning.md
Andy K on Optimizer: The Story So Far (April 2018): https://www.youtube.com/watch?v=wAfAVv9SFIc
Andy Pavlo optimizer lectures
The Cascades Framework for Query Optimization
This is what our optimizer is based on.
Fundamental Techniques for Order Optimization by Simmen et. al
Explains how to manipulate orders, not aware of a publicly available PDF
pkg/sql/opt/doc.go: https://github.com/cockroachdb/cockroach/blob/master/pkg/sql/opt/doc.go
Optimization of Analytic Window Functions: http://vldb.org/pvldb/vol5/p1244_yucao_vldb2012.pdf
...