测试索引

新建50万条数据

for(var i=0;i<500000;i++){db.myusers.insert({"i":i,"username":"user"+i,"age":Math.floor(Math.random()*120),"created":new Date()});}
db.myusers.find({username:"user111"}).explain(true)

{

 ............

 "executionStats" : {

 "executionSuccess" : true,

 "nReturned" : 1,

 "executionTimeMillis" : 238,//-------------

 "totalKeysExamined" : 0,

 "totalDocsExamined" : 500000,//-------------

 "executionStages" : {

 "stage" : "COLLSCAN",//-------------

 "filter" : {

 "username" : {

 "$eq" : "user111"

 },

 ..............

}

增加索引

db.myusers.createIndex({"username":1})
好处:提高查询效率
坏处:数据增删改时会变慢
限制:每个集合最多64个索引

db.myusers.find({username:"user111"}).explain(true)
{

 .................

 "executionStats" : {

 "executionSuccess" : true,

 "nReturned" : 1,

 "executionTimeMillis" : 0, //-------------

 "totalKeysExamined" : 1,

 "totalDocsExamined" : 1,//-------------

 "executionStages" : {

 "stage" : "FETCH",//-------------

 "nReturned" : 1,

 "executionTimeMillisEstimate" : 0,

 .................. 

}

复合索引

索引--{"age":1,"username":1}
db.myusers.find({"age":21}) 高效
db.myusers.find({"age":21}).sort({"username":-1})高效
db.myusers.find({"age":{"$gte":21,"$lte":30}})高效
db.myusers.find({"age":{"$gte":21,"$lte":30}}).sort({"username":-1})一般

特殊索引

创建一个固定集合，最大1000字节，最多100个文档，超过后会自动删除最老的文档
db.createCollection('my_collection',{'capped':true,'size':1000,'max':'100'})

TTL索引

在lastUpdated字段建立TTL索引，当服务器时间比该字段存储的日期类型时间晚86400秒之后，文档立即删除。
Mongodb每分钟对ttl索引执行一次清理
db.my_collection.createIndex({"lastUpdated":1},{"expireAfterSecs":86400})

地理空间索引

2dsphere,用于球体表面，使用GeoJSON格式(geojson.org)
点
{'name':'Sjm','loc':{'type':'Point','coordinates':[116.34,40.02]}}
线
{'name':'River','loc':{'type':'Line','coordinates':[[0,1],[0,2],[1,2]]}}
面
{'name':'Beijing','loc':{'type':'Polygon','coordinates':[[2,1],[2,2],[4,2]]}}

创建索引

db.world.createIndex({'loc':'2dsphere'})
查询
var littleVillage={
'type':'Polygon',
'coordinates':[[-70,30],[-71,40],[-70,38],[-71,40]]
}
与littleVillage有交集的区域的文档:
db.world.find({'loc':{'$geoIntersects':{'$geometry':littleVillage}}})
完全包含在littleVillage区域的文档
db.world.find({'loc':{'$within':{'$geometry':littleVillage}}})
littleVillage区域附近的文档
db.world.find({'loc':{'$near':{'$geometry':littleVillage}}})