Beyond =~: How Milvus 3.0 Turns Regex into a Native Database Filter

This post details the implementation of native regex filtering (`=~`, `!~`) in Milvus 3.0. It covers the design choices for user-facing semantics, the use of raw strings for manageable escaping, the adoption of RE2 for predictable cost and avoidance of ReDoS, and a layered execution path including rewriting simple regex, treating regex as a heavy predicate, using Volnitsky string search for literal prefiltering, and NGRAM indexing for candidate generation. It also addresses the handling of nullability with three-valued logic and the importance of preserving correctness when candidate reduction is not provably safe.