Mongodb: index on subdocument array - node.js

Question

So i have this structure of a document:
{
_id: "123abc",
mainProps: [
{
"countrycode": "US"
},
{
"yearfounded": "2011"
},
{
"city": "New York"
},
...
],
otherProps: [{}, {}, ...]
}
I have an index set like this:
db.companies.ensureIndex({mainProps: 1})
The task is to create a webform for searching in these documents. Fields in the form are not fixed and can be added. Basically i don't know how what fields user would like to filter on, so I can't set proper compound index. Database will be more then 20mil documents, now it's about 10mil.
The problem is that my index doesn't work, or works wrong.
See some examples.
This query has no index at all.
db.companies.find({'mainProps.yearfounded': '2012'}).explain()
This query uses index and is fine.
db.companies.find({mainProps:{'yearfounded': '2012'}}).explain()
And something like this hangs (if I remove the explain() ) and I don't know whether it's executing or what's happening.
db.companies.find(
{$or: [
{ mainProps: {foundedyear: '2012'}},
{ mainProps: {foundedyear: '2011'}},
]}
).explain()
For the last query explain I got something like this.
{
"queryPlanner" : {
"plannerVersion" : 1,
"namespace" : "leadsbase.companies",
"indexFilterSet" : false,
"parsedQuery" : {
"$or" : [
{
"mainProps" : {
"$eq" : {
"foundedyear" : "2012"
}
}
},
{
"mainProps" : {
"$eq" : {
"foundedyear" : "2011"
}
}
}
]
},
"winningPlan" : {
"stage" : "SUBPLAN",
"inputStage" : {
"stage" : "FETCH",
"inputStage" : {
"stage" : "IXSCAN",
"keyPattern" : {
"mainProps" : 1
},
"indexName" : "mainProps_1",
"isMultiKey" : true,
"isUnique" : false,
"isSparse" : false,
"isPartial" : false,
"indexVersion" : 1,
"direction" : "forward",
"indexBounds" : {
"mainProps" : [
"[{ foundedyear: \"2011\
" }, { foundedyear: \"2011\" }]",
"[{ foundedyear: \"2012\
" }, { foundedyear: \"2012\" }]"
]
}
}
}
},
"rejectedPlans" : [ ]
},
"serverInfo" : {
"host" : "vm1",
"port" : 27017,
"version" : "3.2.8",
"gitVersion" : "ed70e33130c977bda0024c125b56d159573dbag0"
},
"ok" : 1
}
So as far as I understand index is present, but for some reason not working.
How should I structure my fields or how should I set indexes for this?

Answer 1

createIndex() will create indexes on collections whereas ensureIndex() creates an index on the specified field if the index does not already exist.
so your second query works while the firstQuery fails. try to delete your index with dropIndex(), and then rebuild the index with createIndex()
One way to check the performance o your indexscan , you can check for "executionStats"
db.collection.explain("executionStats").find( <your query>)
and then from the result, check for this two field:
executionSuccess.totalKeysExamined, executionSuccess.totalDocsExamined
For most case, if your index is good, both should have same number. Or you can read more in documentation
"executionStats" : {
"executionSuccess" : <boolean>,
"nReturned" : <int>,
"executionTimeMillis" : <int>,
"totalKeysExamined" : <int>, // this is your index keys
"totalDocsExamined" : <int>, // this is total docs examined
"executionStages" : {
"stage" : <STAGE1>
"nReturned" : <int>,
"executionTimeMillisEstimate" : <int>,
"works" : <int>,
"advanced" : <int>,
"needTime" : <int>,
"needYield" : <int>,
"isEOF" : <boolean>,
...
"inputStage" : {
"stage" : <STAGE2>,
...
"nReturned" : <int>,
"executionTimeMillisEstimate" : <int>,
"keysExamined" : <int>,
"docsExamined" : <int>,
...
"inputStage" : {
...
}
}
},