MongoDB: 4. Index
來源：程序員人生 發布時間：2014-06-10 18:55:02 閱讀次數：3021次
MongoDB 提供了多樣性的索引支持。
> for (var i = 0; i < 30; i++) {
... u = { name : "user" + i,
... age : 20 + i,
... contact : {
... address : ["address1_" + i, "address2_" + i],
... postcode : 100000 + i,
... }
... };
... db.users.insert(u);
... }
索引信息被保存在 system.indexes 中，且默認總是為 _id 創建索引。
> show collections
system.indexes
users
> db.system.indexes.find()
{ "name" : "_id_", "ns" : "blog.users", "key" : { "_id" : 1 } }
1. ensureIndex / dropIndex / reIndex
使用 ensureIndex 創建索引，dropIndex() 刪除索引，dropIndexes() 刪除全部索引(不包括 _id 等系統索引)。
> db.users.ensureIndex({name:1})
> db.users.ensureIndex({age:1})
> db.system.indexes.find()
{ "name" : "_id_", "ns" : "blog.users", "key" : { "_id" : 1 } }
{ "_id" : ObjectId("4c4a...b798"), "ns" : "blog.users", "key" : { "name" : 1 }, "name" : "name_1" }
{ "_id" : ObjectId("4c4a...b799"), "ns" : "blog.users", "key" : { "age" : 1 }, "name" : "age_1" }
> db.users.dropIndex({age:1})
{ "nIndexesWas" : 3, "ok" : true }
> db.users.dropIndexes()
{
"nIndexesWas" : 2,
"msg" : "non-_id indexes dropped for collection",
"ok" : true
}
> db.system.indexes.find()
{ "name" : "_id_", "ns" : "blog.users", "key" : { "_id" : 1 } }
reIndex 則是重建索引。
> db.users.ensureIndex({name:1})
> db.users.ensureIndex({age:1})
> db.system.indexes.find()
{ "name" : "_id_", "ns" : "blog.users", "key" : { "_id" : 1 } }
{ "_id" : ObjectId("4c4a...b82a"), "ns" : "blog.users", "key" : { "name" : 1 }, "name" : "name_1" }
{ "_id" : ObjectId("4c4a...b82b"), "ns" : "blog.users", "key" : { "age" : 1 }, "name" : "age_1" }
> db.users.reIndex()
{
"nIndexesWas" : 3,
"msg" : "indexes dropped for collection",
"ok" : 1,
"nIndexes" : 3,
"indexes" : [
{
"name" : "_id_",
"ns" : "blog.users",
"key" : {
"_id" : 1
}
},
{
"_id" : ObjectId("4c4a...b82a"),
"ns" : "blog.users",
"key" : {
"name" : 1
},
"name" : "name_1"
},
{
"_id" : ObjectId("4c4a...b82b"),
"ns" : "blog.users",
"key" : {
"age" : 1
},
"name" : "age_1"
}
],
"ok" : 1
}
當系統已有大量數據時，創建索引就是個非常耗時的活，我們可以在后臺執行。
> db.users.dropIndexes()
{
"nIndexesWas" : 3,
"msg" : "non-_id indexes dropped for collection",
"ok" : true
}
> db.users.ensureIndex({name:1}, {backgroud:true})
> db.users.reIndex({backgroud:true})
{
"nIndexesWas" : 2,
"msg" : "indexes dropped for collection",
"ok" : 1,
"nIndexes" : 2,
"indexes" : [
{
"name" : "_id_",
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