Today, PEAK-AIO announced pNFS Lattice, a metadata server for Parallel NFS. It is running on top of RonDB using an RDMA transporter.
Now you might wonder, does RonDB have an RDMA transporter? A few weeks ago the answer would have been no. It has been on the TODO list for more than a decade, but it was not prioritized. However, a few weeks ago Eyal Lemberger from PEAK-AIO contributed an RDMA transporter to RonDB. Me and Eyal worked on the contribution for a few weeks and it was stable enough to integrate into RonDB 26.02, our latest stable release.
In the normal builds, the RDMA transporter is disabled, so it requires manual building to integrate it. The aim is to integrate the RDMA transporter into the RonDB release planned for the end of the year 2026.
3x Latency Improvement
RDMA improved the latency of metadata operations by a factor of 3. Actually, this brings RonDB back to its roots. The very first transporter that NDB Cluster (RonDB is a fork of NDB Cluster) had was a Dolphin SCI transporter. I have worked with Dolphin for more than 30 years. Today Dolphin technology can be used with a normal TCP/IP transporter using normal sockets.
The Wakeup Cost Challenge
The biggest challenge of an RDMA transporter is the same as the challenge of the shared memory transporter. It is about how to wake up the receiving process—it is important not to pay the wakeup cost for every signal.
In RDMA, one can send batches and the wakeup is handled by the network card. Thus, the sender has no cost attached to sending other than writing to the receivers memory. The wakeup cost is only at the receiving side and is integrated in the network card, so the only cost is an occasional interrupt to ensure that the receiver is awake.
Great to see RonDB coming to good use and the open-source license making the technology available to many. Many thanks to PEAK-AIO for the contribution.
