Reading up on ClickHouse
7 deep · digging since dec 01, 25
- I rewrote PostHog's SQL parser, 70x faster, while barely looking at the code
PostHog's engineer used parallel Claude Code sessions to rewrite their SQL parser, achieving a 70x speedup by fuzzing against the old ANTLR-based parser as an oracle.
- Karpathy's Autoresearch found a 3-year-old bug in our query engine (and improved performance by 11%) - PostHog
PostHog used a Karpathy-style AI agent to find a 3-year-old ClickHouse bug where `toTimeZone()` disabled primary key usage, and the fix cut query time by 37%
- Fast regex search: indexing text for agent tools
Cursor is building local indexes for regular expression search to reduce agent wait times from 15-second ripgrep runs in large monorepos.
- Inside our effort to improve the Mintlify assistant
Mintlify used ClickHouse to analyze negative assistant feedback, identified search as the main weakness, and shipped UI improvements like conversation history and mobile chat.
- 28M Hacker News comments as vector embedding search dataset
ClickHouse provides a 28.74-million Hacker News posting dataset with vector embeddings, enabling large-scale vector search application development and testing.