Roundup: Optimising SQL queries and fast software, the best software
Ben Baumann
Aug. 2, 2019
Optimising SQL queries Oskar P
https://towardsdatascience.com/learning-sql-201-optimizing-queries-regardless-of-platform-918a3af9c8b1
This article includes quite a lot of detail about how to optimise SQL queries, covering indexes, index cardinality, index hinting, and more. In my experience, most of the time a site has performance problems it seems to be a poorly-indexed database table, or a query that can never use an index. Have a read of this to figure out what you can tune to resolve these sorts of issues.
Fast Software, The Best Software Oskar P
https://craigmod.com/essays/fast_software/
A compelling discussion on how software speed can be a proxy for overall software quality and focus.