Implementation detail about SET TRANSACTION ISOLATION LEVEL

[marsishandsome]

I'm confused when working on this PR: #10065.

I find that, SET TRANSACTION ISOLATION LEVEL will affect two internal variables:

1. tx_isolation
2. transaction_isolation

Can any body tell me, what's the difference between the two variables?

[lysu]

@marsishandsome

just alias, and mysql's old stuff.

"transaction_isolation was added in MySQL 5.7.20 as an alias for tx_isolation, which is now deprecated and is removed in MySQL 8.0. Applications should be adjusted to use transaction_isolation in preference to tx_isolation."

and there are same history question tx_read_only

Prior to MySQL 5.7.20, use tx_isolation and tx_read_only rather than transaction_isolation and transaction_read_only.