How to use Index in mongodb Database
This article will explain in detail how to use the index in the mongodb database. The content of the article is of high quality, so the editor will share it for you as a reference. I hope you will have a certain understanding of the relevant knowledge after reading this article.
Indexes can accelerate data output in relational databases, as well as non-relational databases, which can reduce disk IO access and have a significant effect on large amounts of data. Currently, mongodb supports the Btel TreeReferenceUniqueParseQuery hash index.
Generate data in a mongodb cluster
[root@node2 mongodb-4.0.8] # / bin/mongo-- host 172.16.8.24-- port 27017
MongoDB shell version v4.0.8
Connecting to: mongodb://172.16.8.24:27017/?gssapiServiceName=mongodb
Implicit session: session {"id": UUID ("a1abbd3a-fe32-46ac-a959-4f8a62abd990")}
MongoDB server version: 4.0.8
Server has startup warnings:
Wuhan:PRIMARY > for (var item1 witch I db.stu.find (). Count ()
one thousand
Wuhan:PRIMARY > db.stu.find ()
{"_ id": ObjectId ("5ca3004015fc3dad4a419a75"), "sn": 1, "name": "student1"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a76"), "sn": 2, "name": "student2"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a77"), "sn": 3, "name": "student3"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a78"), "sn": 4, "name": "student4"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a79"), "sn": 5, "name": "student5"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7a"), "sn": 6, "name": "student6"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7b"), "sn": 7, "name": "student7"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7c"), "sn": 8, "name": "student8"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7d"), "sn": 9, "name": "student9"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7e"), "sn": 10, "name": "student10"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a7f"), "sn": 11, "name": "student11"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a80"), "sn": 12, "name": "student12"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a81"), "sn": 13, "name": "student13"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a82"), "sn": 14, "name": "student14"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a83"), "sn": 15, "name": "student15"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a84"), "sn": 16, "name": "student16"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a85"), "sn": 17, "name": "student17"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a86"), "sn": 18, "name": "student18"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a87"), "sn": 19, "name": "student19"}
{"_ id": ObjectId ("5ca3004015fc3dad4a419a88"), "sn": 20, "name": "student20"}
Type "it" for more
Wuhan:PRIMARY >
I. use of B-Tree index
1. Single-column index use
Wuhan:PRIMARY > db.stu.ensureIndex ({sn:1})-- create an index on the sn field
Wuhan:PRIMARY > db.stu.find ({sn:50}). Explain ();-- check whether the execution plan is indexed
Wuhan:PRIMARY > db.stu.getIndexKeys ()-- see how many keys there are in the table
[{"_ id": 1}, {"sn": 1}]
Wuhan:PRIMARY > db.stu.getIndexes ()-- View all indexes of a table
[{"v": 2, "key": {"_ id": 1}, "name": "_ id_", "ns": "tong.stu"}, {"v": 2, "key": {"sn": 1}, "name": "sn_1", "ns": "tong.stu"}]
Wuhan:PRIMARY > db.stu.dropIndex ({sn:1});-- delete the index of the sn field
Wuhan:PRIMARY > db.stu.dropIndexes ();-- delete all indexes
two。 Use of multi-column indexes
Wuhan:PRIMARY > db.stu.ensureIndex ({name:1}, {name: "IX_name"})-create a multi-column index
{"createdCollectionAutomatically": false, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1, "operationTime": Timestamp (1554188377, 2), "$clusterTime": {"clusterTime": Timestamp (1554188377, 2), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY > db.stu.getIndexes ()-- View index information
[{"v": 2, "key": {"_ id": 1}, "name": "_ id_", "ns": "tong.stu"}, {"v": 2, "key": {"name": 1}, "name": "IX_name", "ns": "tong.stu"}]
Wuhan:PRIMARY > db.stu.dropIndex ({name: "IX_name"})-- delete one of the indexes
{"operationTime": Timestamp (1554188499, 1), "ok": 0, "errmsg": "can't find index with key: {name:\" IX_name\ "}", "code": 27, "codeName": "IndexNotFound", "$clusterTime": {"clusterTime": Timestamp (1554188499, 1), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
3. Subdocument index usage
Wuhan:PRIMARY > db.shop.insert ({name: "Nokia", spc: {weight:120,area: "taiwan"}})-- write data
WriteResult ({"nInserted": 1})
Wuhan:PRIMARY > db.shop.insert ({name: "sanxing", spc: {weight:100,area: "hanguo"}})-- write data
WriteResult ({"nInserted": 1})
Wuhan:PRIMARY > db.shop.find ()-- query data
{"_ id": ObjectId ("5ca337ff15fc3dad4a419e5d"), "name": "Nokia", "spc": {"weight": 120, "area": "taiwan"}}
{"_ id": ObjectId ("5ca3382c15fc3dad4a419e5e"), "name": "sanxing", "spc": {"weight": 100, "area": "hanguo"}}
Wuhan:PRIMARY > db.shop.find ({"spc.area": "hanguo"});-- query the data of the subdocument
{"_ id": ObjectId ("5ca3382c15fc3dad4a419e5e"), "name": "sanxing", "spc": {"weight": 100, "area": "hanguo"}}
Wuhan:PRIMARY > db.shop.ensureIndex ({"spc.area": 1});-- Sub-document creates index
{"createdCollectionAutomatically": false, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1, "operationTime": Timestamp (1554200928, 2), "$clusterTime": {"clusterTime": Timestamp (1554200928, 2), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY > db.shop.getIndexes ()
[{"v": 2, "key": {"_ id": 1}, "name": "_ id_", "ns": "tong.shop"}, {"v": 2, "key": {"spc.area": 1}, "name": "spc.area_1", "ns": "tong.shop"}]
Wuhan:PRIMARY >
two。 Unique index (the field value in the unique index must be unique)
Wuhan:PRIMARY > db.stu.ensureIndex ({name:1}, {unique:true})
{"createdCollectionAutomatically": false, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1, "operationTime": Timestamp (1554188549, 2), "$clusterTime": {"clusterTime": Timestamp (1554188549, 2), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY > db.stu.getIndexes ()
[{"v": 2, "key": {"_ id": 1}, "name": "_ id_", "ns": "tong.stu"}, {"v": 2, "unique": true, "key": {"name": 1}, "name": "name_1", "ns": "tong.stu"}]
Wuhan:PRIMARY > db.stu.totalIndexSize ()-- View the index size
40960
Wuhan:PRIMARY > db.stu.totalSize ()
69632
Wuhan:PRIMARY >
three。 Sparse index (create an index if a field has a value, no value without an index)
Wuhan:PRIMARY > db.shop.find ()
{"_ id": ObjectId ("5ca337ff15fc3dad4a419e5d"), "name": "Nokia", "spc": {"weight": 120, "area": "taiwan"}}
{"_ id": ObjectId ("5ca3382c15fc3dad4a419e5e"), "name": "sanxing", "spc": {"weight": 100, "area": "hanguo"}}
Wuhan:PRIMARY > db.shop.insert ({})-insert a null value
WriteResult ({"nInserted": 1})
Wuhan:PRIMARY > db.shop.find ()
{"_ id": ObjectId ("5ca337ff15fc3dad4a419e5d"), "name": "Nokia", "spc": {"weight": 120, "area": "taiwan"}}
{"_ id": ObjectId ("5ca3382c15fc3dad4a419e5e"), "name": "sanxing", "spc": {"weight": 100, "area": "hanguo"}}
{"_ id": ObjectId ("5ca3419c15fc3dad4a419e5f")}
Wuhan:PRIMARY > db.shop.ensureIndex ({name:1}, {sparse:true});-- create sparse index
{"createdCollectionAutomatically": false, "numIndexesBefore": 2, "numIndexesAfter": 3, "ok": 1, "operationTime": Timestamp (1554203093, 2), "$clusterTime": {"clusterTime": Timestamp (1554203093, 2), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY > db.shop.find ({name: "null"});-- null value is not displayed
Wuhan:PRIMARY >
four。 Hash index
Wuhan:PRIMARY > db.t.ensureIndex ({a: "hashed"})
{"createdCollectionAutomatically": false, "numIndexesBefore": 1, "numIndexesAfter": 2, "ok": 1, "operationTime": Timestamp (1554203661, 2), "$clusterTime": {"clusterTime": Timestamp (1554203661, 2), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY > db.t.find ({a: "25"}) .explain ()
{"queryPlanner": {"plannerVersion": 1, "namespace": "tong.t", "indexFilterSet": false, "parsedQuery": {"a": {"$eq": "25"}}, "winningPlan": {"stage": "FETCH", "filter": {"a": {"$eq": "25"}, "inputStage": {"stage": "IXSCAN" "keyPattern": {"a": "hashed"}, "indexName": "a_hashed"-- displayed as hash index "isMultiKey": false, "isUnique": false, "isSparse": false, "isPartial": false, "indexVersion": 2, "direction": "forward", "indexBounds": {"a": [7200060250846542811,7200060250846542811]]}}, "rejectedPlans": []}} "serverInfo": {"host": "node2", "port": 27017, "version": "4.0.8", "gitVersion": "9b00696ed75f65e1ebc8d635593bed79b290cfbb"}, "ok": 1, "operationTime": Timestamp (1554203690, 1), "$clusterTime": {"clusterTime": Timestamp (1554203690, 1), "signature": {"hash": BinData (0, "AAAAAAAAAAAAAAAAAAAAAAAAAAA="), "keyId": NumberLong (0)}
Wuhan:PRIMARY >
five。 Index rebuilding (when the index is not efficient, you can consider rebuilding the index)
Wuhan:PRIMARY > db.t.reIndex ();-- rebuild the index of t-table
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