pg_mooncake is a Postgres extension that adds a custom table access method ('mooncake') backed by Apache Iceberg, enabling real-time analytics on columnar data stored in Iceberg tables. It integrates DuckDB (via pg_duckdb) as the query engine for fast analytics and provides a background worker (moonlink) that streams changes from regular Postgres heap tables to Iceberg tables via logical replication, ensuring sub-second data freshness. The extension exposes SQL procedures to create columnstore mirrors of Postgres tables, manage snapshots, load files, and optimize storage. It is built using the pgrx framework for Rust-based Postgres extensions and supports Postgres versions 14-18. The architecture is a hybrid of a shared library loaded into the Postgres backend and a separate background worker process. The codebase is well-structured and actively developed, though many table access method callbacks are still stubs, indicating it is in an early but functional stage.