Some notes on Mongo indexes
This article mainly introduces some instructions about Mongo index, which has certain reference value. Now I share it with you. Friends in need can refer to it
Index usage scenarios
Advantages: Speed up the query
Disadvantages: Additions, deletions and modifications will cause additional overhead and occupy space
tips: Return more than half of the data in the collection, and the full table scan is more efficient
Index basics
Basic operations
View index: db.test.getIndexes()
Create index: db.test.ensureIndex({" username":1},{"background":true,"name":"index_test_name"}) //When there is a large amount of data, it can be executed in the background without blocking
Delete the index: db.test.dropIndex({ "username":1})
View the index size: db.test.totalIndexSize()
Attribute
Index order:
1 is positive order, -1 is reverse order
In the composite index, you need to pay attention to the order (id:1, age:-1)
Index attributes:
Uniqueness
db.test.ensureIndex({x:1,y:1},{unique:true})
Sparseness
db.test.ensureIndexx({},{sparse:true/false}) 不稀疏(默认): 1. 可插入不存在索引字段的数据,null; 2. 可筛选不存在字段: db.test.find({m:{$exist:ture}}) 稀疏:
Optimization analysis method
-
explain
Learn how the system handles requests
cursor 返回游标类型(BasicCursor或BtreeCursor) nscanned 被扫描的文档数量 n 返回的文档数 millis 耗时(毫秒) indexBounds 所使用的索引
-
hint
Force the use of an index
db.test.find({"age":20}).hint({"name":1,"age":1}) // .hint(name_1_age_1)
-
profile
Set the log level and record slow queries
##Tips
- Automatically adjust the order of query conditions
- Can hit the index for the prefix regular expression (/^z /)
- Create indexes for keys that require a large amount of sorting to avoid loading all data into memory
- $ne, $nin will not use indexes
- _id index
- Single key index
- Multi-key index
- Compound index
- Expired index
- Full-text index
- Geographical Location Index
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