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Banner: MongoDB compound index reordered by the Equality, Sort, Range rule to remove an in-memory sort

Databases Bug Report

MongoDB query slow despite an index: in-memory SORT and the ESR rule

Daniel Tran · Jun 3, 2025 · 10 min read

A shipment timeline query had a compound index yet still took 2.4 seconds. explain() showed a blocking SORT stage and 180,000 documents examined for 50 results. Reordering the index by Equality, Sort, Range fixed it.

Banner: a PostgreSQL query plan tree with estimated and actual row counts highlighted

Databases

How to read Postgres EXPLAIN ANALYZE output: a practical field guide

Daniel Tran · Apr 22, 2025 · 10 min read

EXPLAIN ANALYZE prints a wall of nodes, costs and loops that most of us skim for the word Seq Scan. This guide walks a real slow query node by node: estimates vs actuals, loops, buffers, and the fixes each pattern points to.