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Type:
Bug
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Resolution: Cannot Reproduce
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Priority:
Major - P3
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None
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Affects Version/s: None
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Component/s: Index Maintenance
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Labels:
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Query Optimization
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ALL
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Query 2020-07-27, Query 2020-08-10, Query 2020-08-24, Query 2020-09-07
In load MongoDB log file, we can see a lot of slow queries. Most of them are not using the best index and consequently the best execution plan is not used. However, when I run the same queries by myself in mongo shell, the correct index is used. So why for same query, we don't have same execution plan ?
Kindly find the log below using wrong index :
2020-05-25T04:55:51.624+0000 I COMMAND [conn301319] command mydb.mycoll command: aggregate { aggregate: "mycoll", pipeline: [ { $match: { networkId.$id: { $in: [ ObjectId('5e0ed9eb60b2533bda7a0fa8') ] }, status: "0", alarmType: "1" } }, { $group: { _id:{ networkId: "$networkId" }, alarmCount: { $sum: 1 } } } ] } planSummary: IXSCAN { status: 1 } keysExamined:35350 docsExamined:35350 numYields:280 nreturned:0 reslen:135 locks:{ Global: { acquireCount:{ r: 574 }, acquireWaitCount: { r: 92 }, timeAcquiringMicros: \{ r: 1590945 } }, Database: { acquireCount:{ r: 287 }}, Collection: { acquireCount:{ r: 286 }} } protocol:op_query 1980ms
Index On collection:
db.getCollection('mycoll').getIndexes()
[
{
"v" : 1,
"key" :{ "_id" : 1 },
"name" : "_id_",
"ns" : "mydb.mycoll"
},
{
"v" : 1,
"key" :{ "networkId.$id" : 1, "status" : 1, "alarmType" : 1 },
"name" : "networkId.$id_1_status_1_alarmType_1",
"ns" : "mydb.mycoll"
},
{
"v" : 2,
"key" :{ "status" : 1 },
"name" : "status_1",
"ns" : "mydb.mycoll",
"background" : true
}
]