Enable fair locking model of pessimistic transactions by default #42147
Description
Enhancement
We've implemented a new locking model for pessimistic transactions, namely Aggressive Locking (and will be renamed to Fair Locking after #42107), which can significantly reduce tail latency in single-key pessimistic lock contention scenarios. Its progress is recorded in this issue.
In 7.0, we plan to enable it by default for new clusters. However for clusters upgraded from older version, it will still be kept disabled to avoid potential risk of performance regression.