We tracked down a memory leak hiding in Meilisearch for 1.5 years – and fixed it by switching to mimalloc v3. Here's what we found, what broke, and how we solved it.

MeiliSearch is an open-source search engine that provides fast and relevant search capabilities for developers. Readers can learn about search algorithms, indexing techniques, and building search functionality into their applications. With documentation, tutorials, and community support, MeiliSearch empowers developers to enhance the search experience for their users.

Meilisearch

A deep investigation into a memory leak in Meilisearch that persisted for 1.5 years. The root cause was twofold: a bumpalo bump allocator misuse where std::Vec objects stored inside bumpalo::Vec never had their drop glue run, and a more significant issue where LMDB (a C library) and Meilisearch used different allocators (system allocator vs mimalloc v2), preventing memory page reuse. Switching to mimalloc v3 with its override feature to unify allocations across both Rust and C code resolved the leak, yielding lower RSS memory usage and performance improvements of around 13% in some benchmarks. The investigation used jemalloc's profiling tools and LLM-assisted heap analysis to identify the issues.

The Good, the Bad, and the Leaky: jemalloc, bumpalo, and mimalloc in Meilisearch

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