Debugging MongoDB queries with explain('executionStats')
totalKeysExamined, totalDocsExamined, nReturned — the three numbers I look at first, and what their ratios tell me before I read a single index.
The ESR rule: how compound indexes really get used
Equality, Sort, Range — the three letters that decide whether your compound index is a thoroughbred or a paperweight. We dissect the planner's prefix-matching logic on a 40M doc collection.
Latest articles
N-gram contains search in MongoDB without paying Atlas Search
How to fake LIKE '%foo%' on Mongo with trigrams, a pre-computed token array, and a clever multikey index. ~12ms p99 on 8M documents.
Five types of scans every backend dev should recognise
Seq scan, index scan, index-only scan, bitmap heap scan, TID scan. When the planner picks each, and what it means when you see the wrong one.
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Postgres tuning: the eight knobs that actually matter
shared_buffers, work_mem, effective_cache_size, and five more — what they really do, how to size them, and which defaults are still stuck in 2008.
Covering indexes: when you can skip the heap entirely
If your index has every column the query needs, the database never has to fetch the row. Here's how to recognise the opportunity — and the storage trade.