June 2020 Summaries

Apache Cassandra is a distributed database system that scales without limits and is used by Ably Realtime for persistent storage of messages. However, the company experienced disruptions in early 2020 due to issues with counter columns in Cassandra. The problem was eventually traced back to excessive retries on an operation involving counter column updates. To resolve the issue, rate limiting was implemented and the use of counter columns was eliminated from the system. This resulted in a significant reduction in load on the Cassandra instances. The experience highlighted the importance of considering practical considerations alongside theoretical knowledge when building distributed systems at scale.

Ably has introduced a new feature called Message Delta Compression that reduces the bandwidth required for transmitting realtime messages by sending only the changes from the previous message instead of the entire message. This feature is now available in Client Library SDKs v1.2, including JavaScript, Java, Cocoa, and .NET versions. By using this technique, developers can optimize their applications' performance while reducing costs associated with bandwidth usage.

This article discusses the implementation of diff algorithms in Ably's distributed pub/sub messaging platform. It provides a detailed overview of diff algorithms, their purpose and usage, three generations of diff algorithms, current delta generation algorithms, delta file formats, testing open-vcdiff and xdelta, and finally, how these concepts were applied at Ably. The article also includes a comparison between the Google Open VCDiff and XDelta algorithms in terms of time complexity and performance.

Ably, a company that provides APIs for developing realtime applications, has issued a statement addressing global racial justice protests. They acknowledge the role of silence, ignorance, and apathy in perpetuating racism, and pledge to contribute to the Minnesota Freedom Fund, matching staff donations to this and other relevant charities. They express their commitment to education as a means of facilitating lasting change and are sharing Anti-Racism resources with staff. Ably also plans to review and adjust their recruitment, staff management, development, and overall business practices to better promote equality. Alongside this, they continue to offer their services for building realtime applications.