MongoDB索引管理——建立索引，查看索引，刪除索引，重建索引

標籤：除了   複合式索引   end   use   key   讀寫   min   導致   指定   

先給users集合插入兩條記錄，然後用users集合來進行索引管理的示範：

> user1={"name":"liming","age":20,"gender":"F"}{ "name" : "liming", "age" : 20, "gender" : "F" }> db.users.insert(user1)WriteResult({ "nInserted" : 1 })> user2={"name":"zhangsan","age":25,"gender":"F"}{ "name" : "zhangsan", "age" : 25, "gender" : "F" }> db.users.insert(user1)WriteResult({ "nInserted" : 1 })> db.users.count()2

建立索引：

mongodb使用createIndex()和ensureIndex()方法來建立索引，前者用於3.0及以上版本，後者用於3.0以下版本。
例1：給name欄位建立正序索引

> db.users.createIndex({"name":1}){    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1}

例2：給name欄位建立倒序索引

> db.users.createIndex({"name":-1}){    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 2,    "numIndexesAfter" : 3,    "ok" : 1}

例3：給name，age欄位建立複合式索引

> db.users.createIndex({"name":1,"age":1}){    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 3,    "numIndexesAfter" : 4,    "ok" : 1}

例4：在後台給age欄位建立索引

> db.users.createIndex({age:1},{background:1}){    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 4,    "numIndexesAfter" : 5,    "ok" : 1}

在後台建立索引的原因：
在前台建立索引期間會鎖定資料庫，會導致其它操作無法進行資料讀寫，在後台建立索引是，會定期釋放寫鎖，從而保證其它操作的運行，但是後台操作會在耗時更長，尤其是在頻繁進行寫入的伺服器上。

查看索引：

MongoDB提供的查看索引資訊的方法：
getIndexes()方法可以用來查看集合的所有索引，
getIndexKeys()方法查看索引鍵。
totalIndexSize()查看集合索引的總大小，
getIndexSpecs()方法查看集合各索引的詳細資料
例1： getIndexes()的用法

> db.users.getIndexes()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1        },        "name" : "name_1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : -1        },        "name" : "name_-1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1,            "age" : 1        },        "name" : "name_1_age_1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "age" : 1        },        "name" : "age_1",        "ns" : "test1.users",        "background" : 1    }]

例2：getIndexKeys()的用法

> db.users.getIndexKeys()[    {        "_id" : 1    },    {        "name" : 1    },    {        "name" : -1    },    {        "name" : 1,        "age" : 1    },    {        "age" : 1    }]

例3：totalIndexSize()的用法

> db.users.totalIndexSize()81920

例4：getIndexSpecs()的用法

> db.users.getIndexSpecs()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1        },        "name" : "name_1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : -1        },        "name" : "name_-1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1,            "age" : 1        },        "name" : "name_1_age_1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "age" : 1        },        "name" : "age_1",        "ns" : "test1.users",        "background" : 1    }]

刪除索引：

不再需要的索引，我們可以將其刪除，mongodb提供兩種刪除索引的方法：
dropIndex()方法用於刪除指定的索引
dropIndexes()方法用於刪除全部的索引
例1:dropIndex()的用法

> db.users.dropIndex("name_1"){ "nIndexesWas" : 5, "ok" : 1 }> db.users.dropIndex("name_1_age_1"){ "nIndexesWas" : 4, "ok" : 1 }> db.users.getIndexSpecs()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : -1        },        "name" : "name_-1",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "age" : 1        },        "name" : "age_1",        "ns" : "test1.users",        "background" : 1    }]

我們可以看到,name欄位的索引和name與age欄位的複合式索引皆被刪除

例2:dropIndexes()的用法

> db.users.dropIndexes(){    "nIndexesWas" : 3,    "msg" : "non-_id indexes dropped for collection",    "ok" : 1}> db.users.getIndexSpecs()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    }]

在使用了dropIndexes()方法後,我們之前建的所有索引都被刪除掉了

索引重建:

我們之前把users的索引全部刪除了,現在在name欄位上建立一個正序索引,然後在name欄位上重建倒序索引,可以看到重建索引是把之前name欄位的索引刪掉再建立一個索引的,重建之前name欄位還是只有一個索引.

> db.users.createIndex({name:1}){    "createdCollectionAutomatically" : false,    "numIndexesBefore" : 1,    "numIndexesAfter" : 2,    "ok" : 1}> db.users.getIndexSpecs()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1        },        "name" : "name_1",        "ns" : "test1.users"    }]> db.users.reIndex({name:-1}){    "nIndexesWas" : 2,    "nIndexes" : 2,    "indexes" : [        {            "key" : {                "_id" : 1            },            "name" : "_id_",            "ns" : "test1.users"        },        {            "key" : {                "name" : 1            },            "name" : "name_1",            "ns" : "test1.users"        }    ],    "ok" : 1}> db.users.getIndexSpecs()[    {        "v" : 1,        "key" : {            "_id" : 1        },        "name" : "_id_",        "ns" : "test1.users"    },    {        "v" : 1,        "key" : {            "name" : 1        },        "name" : "name_1",        "ns" : "test1.users"    }]

MongoDB索引管理——建立索引，查看索引，刪除索引，重建索引