Here's a whole bunch of fascinating reading material I've accumulated these past few months. You can tell there's a lot of love going on for SQL/RDBMS. Then some crazy JVM deployments that make you sit up and wonder. There's also quite a bit of performance related articles on UI/browser technologies. 
Data tier:
Data tier:
- Using Arrays as Materialized Paths in Postgres
 - The Etsy Shard Architecture: Starts With S and Ends With Hard
 - Under the Hood: Automated backups
 - Databus: LinkedIn's low latency change data capture system
 - WAL internals of PostgreSQL
 - SQL on SSDs: Hot and Crazy Love
 - Sharding & IDs at Instagram
 - Counting Triangles Faster
 
- How much memory objects take on JVMs
 - NUMA-Aware Java Heaps for in-memory databases (Watch for the line that says "heaps approaching 1TB" in size! Of course they mean using DirectBuffers but still..)
 
Here's a nice tool that I've filed for later. Esp useful if you find yourself doing production/support calls - Your logs are your data: logstash + elasticsearch. Sort of a poor man's Splunk. 
UI (mostly beating the life out of HTTP and JavaScript):
UI (mostly beating the life out of HTTP and JavaScript):
- Faster Websites: Crash Course on Web Performance
 - How browsers work
 - WebKit in Your Living Room
 - Building the Netflix UI for Wii U
 - High Performance Networking in Google Chrome
 - Talks To Help You Become A Better Front-End Engineer In 2013 (There are some good ones there)
 
JUnit:
- Rules
 - Parameterized tests and its better description here
 - Assumptions
 - Theories and its nicer description here
 - Matchers