MySQL: Architecture..!

Ah..! That's a very basic topic and I'm writing about it now..!! That's because it never lasts in my memory for long time. It always rolls back from my mind , might be because I never felt it's importance - apart from that of interviews !
However, after a brief Googling, here is an overview of MySQL's architecture in my words.

Unlike MS SQL Server or other RDBMS, MySQL doesn't have a standard architecture diagram that we can refer to. Or may be, couldn't find out from the official site of MySQL. 

Anyhow, I was able to get one of the know logical architecture diagram which describes MySQL well and easy to understand is :

That's a 3 layer logical architecture. 

The topmost layer facing the incoming connections/clients includes authentication, security related things.

The second layer is the most important one, which includes Parser, Query Cache and Optimizer.

Parser creates a Parse tree for every query that's been executed by the client. It uses Lex and Yacc compilers (What are they ? That's another big story..,may be in the next to next post..!?!) 

Then the Optimizer tries to optimize this Parse tree by applying different execution plans or by re-writing the query itself. 

This Optimized Parse Tree will be passed on to the third layer which comprise of the Storage engines. Storage engines just gives back the result and don't do any optimization to the query.

Meanwhile, the result sent back will be stored in the query cache to serve the repeating queries.

That's the briefest MySQL architecture, as I understood! Hope that gives an idea of how MySQL works.