MongoDB performance guides
Original, technically reviewed guides with reproducible explain examples. Each guide links directly to the execution plan analyzer.
Reading execution stats
How to interpret nReturned, totalDocsExamined, totalKeysExamined and executionTimeMillis from a MongoDB explain result.
IXSCAN can still be expensive
How a compound index with the wrong fields causes high examination ratios — and how to fix it with a before/after example.
Covered queries
When all queried and projected fields are in the index, MongoDB skips document loading entirely. How to achieve and verify it.
Sharded explain plans
SINGLE_SHARD vs SHARD_MERGE, mergeType, per-shard stats, and what the analyzer currently supports for sharded output.
Related tools
- Execution plan analyzer — paste an explain result and get a visual plan tree
- How it works — how the analyzer normalizes explain output and fires findings