mongodb text index not working - mongodb

Question

mongo3.4.6
hi export, I am new to mongodb, and I have some problem with indexing. below I create a text index on RequestId(string) inside recordInfo collection:
db.getCollection("RecordInfo").createIndex({"RequestId":"text"})
but when I　try to query below:
db.getCollection("RecordInfo").find({"RequestId":"4513456313212313212aaaa"}).explain("executionStats"), you can see it's not using index:
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 17,
"totalKeysExamined" : 0,
"totalDocsExamined" : 9998,
"executionStages" : {
"stage" : "COLLSCAN",
"filter" : {
"RequestId" : {
"$eq" : "4513456313212313212aaaa"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 21,
"works" : 10000,
"advanced" : 1,
"needTime" : 9998,
"needYield" : 0,
"saveState" : 78,
"restoreState" : 78,
"isEOF" : 1,
"invalidates" : 0,
"direction" : "forward",
"docsExamined" : 9998
}
},
then I try below with $text:
db.getCollection("RecordInfo").find({$text:{$search:"4513456313212313212aaaa"}}).explain("executionStats")
it gives me below,which I think pretty good one:
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 1,
"totalKeysExamined" : 1,
"totalDocsExamined" : 1,
"executionStages" : {
"stage" : "TEXT",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 1,
"needTime" : 3,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"indexPrefix" : {
},
"indexName" : "RequestId_text",
"parsedTextQuery" : {
"terms" : [
"4513456313212313212aaaa"
],
"negatedTerms" : [ ],
"phrases" : [ ],
"negatedPhrases" : [ ]
},
"textIndexVersion" : 3,
"inputStage" : {
"stage" : "TEXT_MATCH",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 1,
"needTime" : 3,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsRejected" : 0,
"inputStage" : {
"stage" : "TEXT_OR",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 5,
"advanced" : 1,
"needTime" : 3,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 1,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 1,
"executionTimeMillisEstimate" : 0,
"works" : 2,
"advanced" : 1,
"needTime" : 0,
"needYield" : 0,
"saveState" : 0,
"restoreState" : 0,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"_fts" : "text",
"_ftsx" : 1
},
"indexName" : "RequestId_text",
"isMultiKey" : true,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "backward",
"indexBounds" : {
},
"keysExamined" : 1,
"seeks" : 1,
"dupsTested" : 1,
"dupsDropped" : 0,
"seenInvalidated" : 0
}
}
}
}
},
but why mongo don't use a index by default, so I use hint to force a index query with below:
db.getCollection("RecordInfo").find({"RequestId":"4513456313212313212aaaa"}).hint("RequestId_text").explain("executionStats"), it give me these, which it's not that good:
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 1,
"executionTimeMillis" : 93,
"totalKeysExamined" : 49378,
"totalDocsExamined" : 9998,
"executionStages" : {
"stage" : "FETCH",
"filter" : {
"RequestId" : {
"$eq" : "4513456313212313212aaaa"
}
},
"nReturned" : 1,
"executionTimeMillisEstimate" : 91,
"works" : 49379,
"advanced" : 1,
"needTime" : 49377,
"needYield" : 0,
"saveState" : 386,
"restoreState" : 386,
"isEOF" : 1,
"invalidates" : 0,
"docsExamined" : 9998,
"alreadyHasObj" : 0,
"inputStage" : {
"stage" : "IXSCAN",
"nReturned" : 9998,
"executionTimeMillisEstimate" : 50,
"works" : 49379,
"advanced" : 9998,
"needTime" : 39380,
"needYield" : 0,
"saveState" : 386,
"restoreState" : 386,
"isEOF" : 1,
"invalidates" : 0,
"keyPattern" : {
"_fts" : "text",
"_ftsx" : 1
},
"indexName" : "RequestId_text",
"isMultiKey" : true,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 2,
"direction" : "forward",
"indexBounds" : {
"_fts" : [
"[MinKey, MaxKey]"
],
"_ftsx" : [
"[MinKey, MaxKey]"
]
},
"keysExamined" : 49378,
"seeks" : 1,
"dupsTested" : 49378,
"dupsDropped" : 39380,
"seenInvalidated" : 0
}
}
},
To summaize, I want to use index or whatever method to query RequestId field which is string column fast. but if I force to use index, it seems not work for me only make my query worse. but if I use index another way, like below, I can see a pretty good query. but I can't specify on wich field I want to query this way.
db.getCollection("RecordInfo").find({$text:{$search:"4513456313212313212aaaa"}}).explain("executionStats")

Answer 1

Text search only works using the $text query operator.
When you execute db.getCollection("RecordInfo").find({"RequestId":"4513456313212313212aaaa"}), you're running a query for an exact match on that field.
From the question, it seems what you're looking for is a regular index, which you can create using db.getCollection("RecordInfo").createIndex({"RequestId": 1})
This will make your query using $text fail (because there is no text index) but will make the regular one use the index and avoid COLLSCAN.