![[str_idx_ivfflat.png|256]] - **Description**: Divides vector space into clusters (lists) and searches only the most relevant ones. Faster to build and uses less memory than HNSW, but with lower query throughput. - **Extension**: Requires `pgvector`. - **Supported Operators**: `<->`, `<#>`, `<=>`, `<+>` (L1 distance). - **Key Parameters**: - `lists`: Number of clusters to create (training required). - `probes`: Number of clusters to search during a query (runtime tuning). - **Metaphor**: A city map divided into distinct neighborhoods. Instead of searching every house in the city, you identify the 2 or 3 neighborhoods most likely to contain your target and only search there.