Description:

------------

These path introduces several improvement for InnoDB read-only

workload:

1. Remove trx_sys_t::ro_trx_list, all transaction will start with

read only mode, and change to rw mode while encountering DML

statement. For more details, refer to mysql worklog WL#6047.

2. Read view object is cached for read-only statement if no rw

statement happens during two read only statements of the same

session.

3. Ignore acquiring lock_sys mutex contention while commiting

read only transaction.