Function tikv::storage::txn::acquire_pessimistic_lock

pub fn acquire_pessimistic_lock<S: Snapshot>(
    txn: &mut MvccTxn, 
    reader: &mut SnapshotReader<S>, 
    key: Key, 
    primary: &[u8], 
    should_not_exist: bool, 
    lock_ttl: u64, 
    for_update_ts: TimeStamp, 
    need_value: bool, 
    min_commit_ts: TimeStamp, 
    need_old_value: bool
) -> MvccResult<(Option<Value>, OldValue)>