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One-hash Bloom filters can spare Bluesky millions of database queries per second

calabro.io 6 min read Editor score 7/10

Bloom filters can rule out keys without disk access, and Bluesky uses them to avoid millions of Scylla queries per second. The post explores a one-hash variant with potential lessons for latency-sensitive data systems.

What

Bloom filters are probabilistic set-membership structures that answer “definitely not” or “probably” using little memory.

How

Bluesky loads blocks, mutes and list items into filters; a real-time firehose consumer adds new items.

Why it matters

A roughly 1% positive hit rate lets Bluesky skip database queries 99% of the time, helping it scale and operate cheaply.

Read on calabro.io → Lobsters · 8 comments

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