Extended RUM in DocumentDB extension for PostgreSQL: Efficient ESR (Equality, Sort, Range) Queries
Last year, I examined RUM indexes within this series on multi-key indexing, demonstrating that they cannot substitute MongoDB's compound indexes for sorted queries. A year later, Microsoft has fixed this in the DocumentDB extension for PostgreSQL with an Extended RUM index that preserves the ordering of the keys, allowing an ordered scan rather than a bitmap scan. Let's revisit our pagination query to see how it performs now. I start a container with the latest DocumentDB (version v0.112-0 from May 26, 2026): docker run -d --name documentdb-local -p 10260:10260 -p 9712:9712 ghcr.io/documentdb/documentdb/documentdb-local:latest --username franck --password franck --start-pg I can connect to PostgreSQL on port 9712, where many extensions are installed, including the extended RUM index: docker exec -it documentdb-local psql -p 9712 postgres psql ( 17.10 ( Debian 17.10-1.pgdg13+1 )) Type "help" for help. postgres = # \dx List of installed extensions Name | Version | Schema | Description ------------------------- +---------+------------+------------------------------------------------------------ documentdb | 0.112-0 | public | API surface for DocumentDB for PostgreSQL documentdb_core | 0.112-0 | public | Core API surface for DocumentDB on PostgreSQL documentdb_extended_rum | 0.112-0 | public | DocumentDB Extended RUM index access method pg_cron | 1.6 | pg_catalog | Job scheduler for PostgreSQL plpgsql | 1.0 | pg_catalog | PL/pgSQL procedural language postgis | 3.6.3 | public | PostGIS geometry and geography spatial types and functions tsm_system_rows | 1.0 | public | TABLESAMPLE method which accepts number of rows as a limit vector | 0.8.2 | public | vector data type and ivfflat and hnsw access methods ( 8 rows ) postgres = # I can also connect to the MongoDB-compatible API: docker exec -it documentdb-local mongosh -u franck -p franck 'mongodb://localhost:10260/?tls=true&tlsAllowInvalidCertificates=true' Current Mongosh Log ID: 6a0b3b537d2a1c3471d1a7ba Connecting to: mo