Announcement from the HDF Group: First Alpha release of VFD SWMR


The HDF Group and Akadio are pleased to announce the first pre-release of the HDF5 library with support for the new Single-Writer/Multiple Reader (SWMR) capability, called “VFD SWMR.” VFD SWMR is designed to be a more flexible, more modular, and better-performing replacement for the existing HDF5 SWMR feature.

The VFD SWMR pre-release can be obtained from this Bitbucket repo.

We have included you in this email because you or your organization at some time expressed interest in this new version of SWMR. We hope you will try it out.

A special VFD SWMR mailing list ( and hdf forum category has been created for you to ask questions and report issues and other experiences. The attached document explains how the list works and how to subscribe and unsubscribe from the list.

  • If you have an HDF forum account, you have already been subscribed.

  • If you don’t have a forum account, the attached document explains how to join.

In the repo doc
directory, the document “" has instructions on using VFD SWMR, and “VFD_SWMR_RFC_200916.pdf” describes the architecture and implementation.

More about VFD SWMR. SWMR is a feature of the HDF5 library that lets a process write data to an HDF5 file while one or more processes reads from the file. Use cases range from monitoring data collection and/or steering experiments to financial applications.

VFD SWMR is designed to be a more flexible, more modular, better-performing replacement for the existing SWMR feature.

  • VFD SWMR allows HDF5 objects (groups, datasets, attributes) to be created and destroyed in the course of a reader-writer session. Creating and destroying objects is not possible using the existing SWMR feature.

  • It compartmentalizes much of the SWMR functionality
    in the bottom layers of the HDF5 library, which both eases the HDF Group’s software maintenance burden, and allows non-SWMR applications to avoid SWMR related overhead.

  • And it makes guarantees for the maximum time from write to availability of data for read, provided that the reading and writing systems and their interconnections can keep up with the data flow.
    For details about the VFD SWMR architecture, see the RFC.



How to use the SWMR VFD Mailing List.pdf (94.1 KB)