you06

@cfzjywxk @sticnarf can you give some advice on this document?

I added the railroad diagrams and here is a screenshot of doc page. @cfzjywxk @sticnarf PTAL again.

@shichun-0415 PTAL

@tisonkun I created the issues for transaction sections, can you help to assign these issues and add them to the tracing list?

How the temp mutations of optimistic transactions are buffered in TiDB may be discussed.

There are still some format issues: - The bold marks are not work in code blocks, which should be removed. - The main body's function names are in quotation marks,...

rest LGTM

@wshwsh12 PTAL

> @you06 Any update? I'm fixing the tests broken by this PR.

> Any bench result to show the great improvement of this change? I attached the bench result to the description.