system.indexes下包含所有索引信息

自动创建的有每个集合的_id和shard key索引

mongos> db.system.indexes.find();
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.doc1" }
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.doc0" }
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.doc2" }
{ "v" : 1, "key" : { "int1" : 1, "int2" : 1 }, "name" : "int1_1_int2_1", "ns" : "test.doc0" }
{ "v" : 1, "key" : { "datee" : 1 }, "name" : "datee_1", "ns" : "test.doc1" }
{ "v" : 1, "key" : { "_id" : "hashed" }, "name" : "_id_hashed", "ns" : "test.doc2" }
{ "v" : 1, "key" : { "int1" : 1 }, "name" : "int1_1", "ns" : "test.doc2" }

创建单列索引

mongos> db.doc2.createIndex({int1: 1});
{
     "raw" : {
          "rs0/rs0-1:4021,rs0-2:4022" : {
               "createdCollectionAutomatically" : false,
               "numIndexesBefore" : 2,
               "numIndexesAfter" : 3,
               "ok" : 1,
               "$gleStats" : {
                    "lastOpTime" : Timestamp(1427783921, 1),
                    "electionId" : ObjectId("551a2ae2990be7dcbb04bc36")
               }
          },
          "rs1/rs1-1:4031,rs1-2:4032" : {
               "createdCollectionAutomatically" : false,
               "numIndexesBefore" : 2,
               "numIndexesAfter" : 3,
               "ok" : 1,
               "$gleStats" : {
                    "lastOpTime" : Timestamp(1427783920, 1),
                    "electionId" : ObjectId("551a2ae0533749e2a0afdff5")
               }
          },
          "rs2/rs2-1:4041,rs2-2:4042" : {
               "createdCollectionAutomatically" : false,
               "numIndexesBefore" : 2,
               "numIndexesAfter" : 3,
               "ok" : 1,
               "$gleStats" : {
                    "lastOpTime" : Timestamp(1427783920, 1),
                    "electionId" : ObjectId("551a2ae17178e928a24df7d7")
               }
          },
          "rs3/rs3-1:4051,rs3-2:4052" : {
               "createdCollectionAutomatically" : false,
               "numIndexesBefore" : 2,
               "numIndexesAfter" : 3,
               "ok" : 1,
               "$gleStats" : {
                    "lastOpTime" : Timestamp(1427783921, 1),
                    "electionId" : ObjectId("551a2aec443124be35cfec75")
               }
          }
     },
     "ok" : 1
}

mongos> db.addr.insert(
... {
...  "name": "John Doe",
...  "address": {
...         "street": "Main",
...         "zipcode": "53511",
...         "state": "WI"
...         }
... });
WriteResult({ "nInserted" : 1 })

在内嵌对象上创建索引 
db.addr.createIndex( { "address.zipcode": 1 } );

甚至直接为整个内嵌文档创建索引

db.addr.createIndex( { address: 1 });

复合索引

mongos> db.addr.insert(
...   {
...     id: 1,
...     name: "a"
...   }
... );

db.addr.createIndex({id:1, name:1});

复合索引的限制

符合索引的某个键可以是数组

mongos> db.addr.insert(

...   {

...     id: [1,2],

...     name: "a"

...   }

... );

WriteResult({ "nInserted" : 1 })

mongos> db.addr.insert({

...     id: 1,

...     name: ["x","y"]

...   }

... );

WriteResult({ "nInserted" : 1 })

但是不能有两个键的值都是数组

mongos> db.addr.insert({

...     id: [1,2],

...     name: ["x","y"]

...   }

... );

WriteResult({

"nInserted" : 0,

"writeError" : {

"code" : 10088,

"errmsg" : "cannot index parallel arrays [name] [id]"

}

})

multikey索引

mongos> db.addr.insert(
...   {
...     id: 1,
...     name: "a",
...     zips: [
...       {zipcode: 111},
...       {zipcode: 222},
...       {zipcode: 333}
...     ]
...   }
... );

上面addr的zips，是一个数组，里面有多个zipcode。可以用

db.addr.createIndex({'zips.zipcode': 1});

multikey索引的限制

shard key无法做multikey

哈希索引

和oracle一样，不支持范围扫描

db.aaa.createIndex( { a: "hashed" } )

TTL索引

数据插入一定时间后自动删除数据，单位是秒。

索引的字段必须是日期型，或包含日期类型的字段。

只支持单列索引。

db.doc2.createIndex({dt:1}, {expireAfterSeconds: 10})

db.doc2.insert({int1:99999, dt:new Date()})

...

...

上面设置的是10秒，但不一定真的能在10秒的时候删除。

sparse索引

这种索引只存储那些包含索引字段的文档，包括空值的。

db.doc2.createIndex( { "int2": 1 }, { sparse: true } )

后台创建索引

默认情况下创建索引会阻塞数据库上所有操作，除非指定后台创建。

指定后台创建时，只有当前session会被阻塞。

进行后台创建时，无法进行其它与这个集合相关的管理类操作。

db.doc2.createIndex( { int3: 1}, {background: true} )

删除索引

mongos> db.system.indexes.find({ns: "test.doc2"})
{ "v" : 1, "key" : { "_id" : 1 }, "name" : "_id_", "ns" : "test.doc2" }
{ "v" : 1, "key" : { "_id" : "hashed" }, "name" : "_id_hashed", "ns" : "test.doc2" }
{ "v" : 1, "key" : { "int1" : 1 }, "name" : "int1_1", "ns" : "test.doc2" }

db.doc2.dropIndex("int1_1")