  Concurrency control protocols are the key to scaling current DBMS
performances. They efficiently interleave read and write operations in
transactions, but occasionally they restrict concurrency by using coordination
such as exclusive lockings. Although exclusive lockings ensure the correctness
of DBMS, it incurs serious performance penalties on multi-core environments. In
particular, existing protocols generally suffer from emerging highly write
contended workloads, since they use innumerable lockings for write operations.
In this paper, we rethink the Thomas write rule (TWR), which allows the
timestamp ordering (T/O) protocol to omit write operations without any
lockings. We formalize the notion of omitting and decouple it from the T/O
protocol implementation, in order to define a new rule named non-visible write
rule (NWR). When the rules of NWR are satisfied, any protocol can in theory
generate omittable write operations with preserving the correctness without any
lockings. In the experiments, we implement three NWR-extended protocols:
Silo+NWR, TicToc+NWR, and MVTO+NWR. Experimental results demonstrate the
efficiency and the low-overhead property of the extended protocols. We confirm
that NWR-extended protocols achieve more than 11x faster than the originals in
the best case of highly write contended YCSB-A and comparable performance with
the originals in the other workloads.
