Writing about MongoDB from the people building a MongoDB IDE. Query plans, schema cost, and what the server actually does on your version.https://monghoul.com/en-ushttps://monghoul.com/blog/mongodb-mcp-server-scope/https://monghoul.com/blog/mongodb-mcp-server-scope/The official server writes unless you pass --readOnly, its confirmations depend on the client supporting elicitation, and its Atlas tools create users.Sun, 13 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/aggregation-stages-by-version/https://monghoul.com/blog/aggregation-stages-by-version/The answer to "why does $percentile not work" is almost always the server version. Here is what arrived in each release from 5.0 to 8.3.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/allow-disk-use-by-default/https://monghoul.com/blog/allow-disk-use-by-default/Most guides say a stage over 100 MB errors unless you pass allowDiskUse. That has been wrong since MongoDB 6.0, and the new failure is quiet.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/bsonobjecttoolarge/https://monghoul.com/blog/bsonobjecttoolarge/The 16 MB limit is on the encoded document, not on what you think you stored. The usual culprit is an array nobody bounded.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/extended-json-pitfalls/https://monghoul.com/blog/extended-json-pitfalls/JSON has no date type and no 64-bit integer. Extended JSON has both, in two modes, and relaxed mode loses less than people think and more than they check.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/index-field-order/https://monghoul.com/blog/index-field-order/The same three fields in a different order decides whether the index serves your sort or the server does it in memory. The plan says which you have.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/indexed-and-still-slow/https://monghoul.com/blog/indexed-and-still-slow/An IXSCAN in the plan is not the finish line. The number that matters is how many documents the server had to read to return the ones you asked for.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/lookup-vs-embedding-measured/https://monghoul.com/blog/lookup-vs-embedding-measured/A $lookup on an indexed key cost nothing here. Sorting on the joined field cost nine seconds. The gap between those two is the whole decision.Mon, 07 Sep 2026 00:00:00 GMThttps://monghoul.com/blog/mongodb-mcp-read-only/https://monghoul.com/blog/mongodb-mcp-read-only/A read-only flag that works by reading the query text can be walked past in four lines. Where the check runs matters more than what it is called.Mon, 07 Sep 2026 00:00:00 GMT