mongodb-usage — Анализ и оптимизация производительности MongoDB

--- name: mongodb-usage description: This skill should be used when user asks to "query MongoDB", "show database collections", "get collection schema", "list MongoDB databases", "search records in MongoDB", or "check database indexes". --- # MongoDB Best Practices ## MCP Limitation **This MCP operates in READ-ONLY mode.** No write, update, or delete operations are possible. ## Schema Design Patterns ### Embedding vs Referencing **Embed when:** - Data is accessed together frequently - Child documents are bounded (won't grow unbounded) - One-to-few relationships - Data doesn't change frequently **Reference when:** - Data is accessed independently - Many-to-many relationships - Documents would exceed 16MB limit - Frequent updates to referenced data ### Common Patterns **Subset pattern:** Store frequently accessed subset in parent, full data in separate collection. **Bucket pattern:** Group time-series data into buckets (e.g., hourly readings in one document). **Computed pattern:** Store pre-computed values for expensive calculations. ## Index Strategies ### Index Guidelines - Index fields used in queries, sorts, and aggregation $match stages - Compound indexes support queries on prefix fields - Covered queries (all fields in index) are fastest - Too many indexes slow writes ### Index Types - **Single field:** Basic index on one field - **Compound:** Multiple fields, order matters for queries - **Multikey:** Automatically created for array fields - **Text:** Full-text search on string content - **TTL:** Auto-expire documents after time period ### ESR Rule For compound indexes, order fields by: 1. **E**quality (exact match fields) 2. **S**ort (sort order fields) 3. **R**ange (range query fields like $gt, $lt) ## Aggregation Pipeline ### Performance Tips - Put `$match` and `$project` early to reduce documents - Use `$limit` early when possible - Avoid `$lookup` on large collections without indexes - Use `$facet` for multiple aggregations in one query ### Common Stages ```javascript // Filter documents { $match: { status: "active" } } // Reshape documents { $project: { name: 1, total: { $sum: "$items.price" } } } // Group and aggregate { $group: { _id: "$category", count: { $sum: 1 } } } // Sort results { $sort: { count: -1 } } // Join collections { $lookup: { from: "orders", localField: "_id", foreignField: "userId", as: "orders" } } ``` ## Connection Best Practices ### Connection String Formats - **Atlas:** `mongodb+srv://user:pass@cluster.mongodb.net/database` - **Local:** `mongodb://localhost:27017/database` - **Replica set:** `mongodb://host1,host2,host3/database?replicaSet=rs0` ### Connection Pooling - Use connection pooling in applications (default in drivers) - Set appropriate pool size for your workload - Don't create new connections per request ## Anti-Patterns to Avoid - **Unbounded arrays:** Arrays that grow without limit - **Massive documents:** Documents approaching 16MB - **Too many collections:** Use embedding instead - **Missing indexes:** Queries doing collection scans - **$where operator:** Use aggregation instead for security - **Storing files in documents:** Use GridFS for large files