Replace unnecessary Lock()/Unlock()s with RLock()/RUnlock()s

[CaojiamingAlan]

What would you like to be added?

Follow up #16068 (comment)
There are some read transactions use Lock()/Unlock() when trying to get data from backend. We should replace them with RLock()/RUnlock() to allow more concurrent reads.

• Current main branch Replace unnecessary Lock()/Unlock()s with RLock()/RUnlock()s #16248
• Backport to 3.5 [3.5]Replace unnecessary Lock()/Unlock()s with RLock()/RUnlock()s #16297
• Backport to 3.4 [3.4]Replace unnecessary Lock()/Unlock()s with RLock()/RUnlock()s #16298

Why is this needed?

Improve concurrency