[cricketlover]

Good post but given my lack of experience, I could only follow about half of it.

What would be a good place for me to understand how Query Processing Engines excute and optimise in general? I want to see and understand actual system calls behind them.

[ChrisWint]

I can recommend the lecture for implementing database systems by Thomas Neumann, who spearheaded the Umbra system which CedarDB builds on. The slides and lecture recordings are available online:

https://db.in.tum.de/teaching/ss21/moderndbs/