查看执行计划的方法：explain （）

winningPlan是最终的执行计划 其中的indexBounds索引计划

1. 在age上建立索引
2. > db.person.ensureIndex({age:1});
3. {
4.    "createdCollectionAutomatically" : false,
5.    "numIndexesBefore" : 1,
6.    "numIndexesAfter" : 2,
7.    "ok" : 1
8. }
9. > db.person.getIndexes();
10. [
11.    {
12.       "v" : 1,
13.       "key" : {
14.          "_id" : 1
15.       },
16.       "name" : "_id_",
17.       "ns" : "mydb.person"
18.    },
19.    {
20.       "v" : 1,
21.       "key" : {
22.          "age" : 1
23.       },
24.       "name" : "age_1",
25.       "ns" : "mydb.person"
26.    }
27. ]
28. 查看执行计划 indexBounds可以看到走了age的索引
29. > db.person.find({age:30}).explain();
30. {
31.    "queryPlanner" : {
32.       "plannerVersion" : 1,
33.       "namespace" : "mydb.person",
34.       "indexFilterSet" : false,
35.       "parsedQuery" : {
36.          "age" : {
37.             "$eq" : 30
38.          }
39.       },
40.       "winningPlan" : {
41.          "stage" : "FETCH",
42.          "inputStage" : {
43.             "stage" : "IXSCAN",
44.             "keyPattern" : {
45.                "age" : 1
46.             },
47.             "indexName" : "age_1",
48.             "isMultiKey" : false,
49.             "direction" : "forward",
50.             "indexBounds" : {
51.                "age" : [
52.                   "[30.0, 30.0]"
53.                ]
54.             }
55.          }
56.       },
57.       "rejectedPlans" : [ ]
58.    },
59.    "serverInfo" : {
60.       "host" : "localhost.localdomain",
61.       "port" : 27017,
62.       "version" : "3.0.6",
63.       "gitVersion" : "1ef45a23a4c5e3480ac919b28afcba3c615488f2"
64.    },
65.    "ok" : 1
66. }
67. 没有走索引的计划是这样的
68. > db.person.find({name:‘zjf‘}).explain();
69. {
70.    "queryPlanner" : {
71.       "plannerVersion" : 1,
72.       "namespace" : "mydb.person",
73.       "indexFilterSet" : false,
74.       "parsedQuery" : {
75.          "name" : {
76.             "$eq" : "zjf"
77.          }
78.       },
79.       "winningPlan" : {
80.          "stage" : "COLLSCAN",
81.          "filter" : {
82.             "name" : {
83.                "$eq" : "zjf"
84.             }
85.          },
86.          "direction" : "forward"
87.       },
88.       "rejectedPlans" : [ ]
89.    },
90.    "serverInfo" : {
91.       "host" : "localhost.localdomain",
92.       "port" : 27017,
93.       "version" : "3.0.6",
94.       "gitVersion" : "1ef45a23a4c5e3480ac919b28afcba3c615488f2"
95.    },
96.    "ok" : 1
97. }

强制索引 hint()方法：

1. > db.person.ensureIndex({name:1,age:1});
2. {
3.    "createdCollectionAutomatically" : false,
4.    "numIndexesBefore" : 3,
5.    "numIndexesAfter" : 4,
6.    "ok" : 1
7. }
8. > db.person.getIndexes();
9. [
10.    {
11.       "v" : 1,
12.       "key" : {
13.          "_id" : 1
14.       },
15.       "name" : "_id_",
16.       "ns" : "mydb.person"
17.    },
18.    {
19.       "v" : 1,
20.       "key" : {
21.          "age" : 1
22.       },
23.       "name" : "age_1",
24.       "ns" : "mydb.person"
25.    },
26.    {
27.       "v" : 1,
28.       "key" : {
29.          "name" : 1
30.       },
31.       "name" : "name_1",
32.       "ns" : "mydb.person"
33.    },
34.    {
35.       "v" : 1,
36.       "key" : {
37.          "name" : 1,
38.          "age" : 1
39.       },
40.       "name" : "name_1_age_1",
41.       "ns" : "mydb.person"
42.    }
43. ]
44. //如果不加hint 默认走age上的索引。
45. > db.person.find({age:{$gt:0}}).explain();
46. {
47.    "queryPlanner" : {
48.       "plannerVersion" : 1,
49.       "namespace" : "mydb.person",
50.       "indexFilterSet" : false,
51.       "parsedQuery" : {
52.          "age" : {
53.             "$gt" : 0
54.          }
55.       },
56.       "winningPlan" : {
57.          "stage" : "FETCH",
58.          "inputStage" : {
59.             "stage" : "IXSCAN",
60.             "keyPattern" : {
61.                "age" : 1
62.             },
63.             "indexName" : "age_1",
64.             "isMultiKey" : false,
65.             "direction" : "forward",
66.             "indexBounds" : {
67.                "age" : [
68.                   "(0.0, inf.0]"
69.                ]
70.             }
71.          }
72.       },
73.       "rejectedPlans" : [ ]
74.    },
75.    "serverInfo" : {
76.       "host" : "localhost.localdomain",
77.       "port" : 27017,
78.       "version" : "3.0.6",
79.       "gitVersion" : "1ef45a23a4c5e3480ac919b28afcba3c615488f2"
80.    },
81.    "ok" : 1
82. }
83. //使用hint
84. > db.person.find({age:{$gt:0}}).hint({name:1,age:1}).explain();
85. {
86.    "queryPlanner" : {
87.       "plannerVersion" : 1,
88.       "namespace" : "mydb.person",
89.       "indexFilterSet" : false,
90.       "parsedQuery" : {
91.          "age" : {
92.             "$gt" : 0
93.          }
94.       },
95.       "winningPlan" : {
96.          "stage" : "KEEP_MUTATIONS",
97.          "inputStage" : {
98.             "stage" : "FETCH",
99.             "filter" : {
100.                "age" : {
101.                   "$gt" : 0
102.                }
103.             },
104.             "inputStage" : {
105.                "stage" : "IXSCAN",
106.                "keyPattern" : {
107.                   "name" : 1,
108.                   "age" : 1
109.                },
110.                "indexName" : "name_1_age_1",
111.                "isMultiKey" : false,
112.                "direction" : "forward",
113.                "indexBounds" : {
114.                   "name" : [
115.                      "[MinKey, MaxKey]"
116.                   ],
117.                   "age" : [
118.                      "[MinKey, MaxKey]"
119.                   ]
120.                }
121.             }
122.          }
123.       },
124.       "rejectedPlans" : [ ]
125.    },
126.    "serverInfo" : {
127.       "host" : "localhost.localdomain",
128.       "port" : 27017,
129.       "version" : "3.0.6",
130.       "gitVersion" : "1ef45a23a4c5e3480ac919b28afcba3c615488f2"
131.    },
132.    "ok" : 1
133. }

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