Items tagged scaling, cassandra
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How Discord Stores Trillions of Messages (via) This is a really interesting case-study. Discord migrated from MongoDB to Cassandra back in 2016 to handle billions of messages. Today they’re handling trillions, and they completed a migration from Cassandra to Scylla, a Cassandra-like data store written in C++ (as opposed to Cassandra’s Java) to help avoid problems like GC pauses. In addition to being a really good scaling war story this has some interesting details about their increased usage of Rust. As a fan of request coalescing (which I’ve previously referred to as dogpile prevention) I particularly liked this bit:
“Our data services sit between the API and our ScyllaDB clusters. They contain roughly one gRPC endpoint per database query and intentionally contain no business logic. The big feature our data services provide is request coalescing. If multiple users are requesting the same row at the same time, we’ll only query the database once. The first user that makes a request causes a worker task to spin up in the service. Subsequent requests will check for the existence of that task and subscribe to it. That worker task will query the database and return the row to all subscribers.” # 8th March 2023, 7:07 pm
How Discord Stores Billions of Messages (via) Fascinating article from 2017 describing how Discord migrated their primary message store to Cassandra (from MongoDB, but I could easily see them making the same decision if they had started with PostgreSQL or MySQL). The trick with scalable NoSQL databases like Cassandra is that you need to have a very deep understanding of the kinds of queries you will need to answer—and Discord had exactly that. In the article they talk about their desire to eventually migrate to Scylla (a compatible Cassandra alternative written in C++)—in the Hacker News comments they confirm that in 2021 they are using Scylla for a few things but they still have their core messages in Cassandra. # 24th August 2021, 9:31 pm
Up and running with Cassandra. Twitter are beginning to use Cassandra, the open source branch of Facebook’s BigTable-like non-relational database. Evan Weaver explains how to get started with it, but warns that it’s not yet a good idea to trust data to it without having a full backup in an unrelated storage engine. # 7th July 2009, 11:18 am