NeedSetRCCheckTSFlag checks whether it's needed to set `RCCheckTS` flag in current stmtctx.

NewPessimisticRCTxnContextProvider returns a new PessimisticRCTxnContextProvider.

NewPessimisticRRTxnContextProvider returns a new PessimisticRRTxnContextProvider.

NewPessimisticSerializableTxnContextProvider returns a new PessimisticSerializableTxnContextProvider.

OptimisticTxnContextProvider provides txn context for optimistic transaction.

PessimisticRCTxnContextProvider provides txn context for isolation level read-committed.

PessimisticRRTxnContextProvider provides txn context for isolation level repeatable-read.

PessimisticSerializableTxnContextProvider provides txn context for isolation level oracle-like serializable.