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Type:
Bug
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Resolution: Duplicate
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Priority:
Major - P3
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None
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Affects Version/s: 3.0.6, 3.0.7
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Component/s: Querying
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ALL
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Hi!
I have noticed that MongoDB won't use indexes when querying for a distinct value on a field. I will use it on some fields, but won't on others.
Here's the example:
db.product.createIndex({"_indexed.preventieve_mondzorg-max_bedrag_p_jr": 1});
db.runCommand({distinct: "product", key:"_indexed.preventieve_mondzorg-max_bedrag_p_jr"});
And that's what it produces:
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 50,
"numIndexesAfter" : 50,
"note" : "all indexes already exist",
"ok" : 1
}
{
"values" : [
"€ 250,- | 75%",
"Geen dekking",
"...",
],
"stats" : {
"n" : 33660,
"nscanned" : 0,
"nscannedObjects" : 33660,
"timems" : 12531,
"planSummary" : "COLLSCAN"
},
"ok" : 1
}
On the other hand
db.product.createIndex({"free_choice.value": 1});
db.runCommand({distinct: "product", key:"free_choice.value"});
Will the index:
{
"createdCollectionAutomatically" : false,
"numIndexesBefore" : 50,
"numIndexesAfter" : 50,
"note" : "all indexes already exist",
"ok" : 1
}
{
"values" : [
"gedeeltelijk",
"geen",
"ja"
],
"stats" : {
"n" : 4,
"nscanned" : 4,
"nscannedObjects" : 4,
"timems" : 2,
"planSummary" : "DISTINCT { free_choice.value: 1.0 }"
},
"ok" : 1
}
So... what could be the difference between those two fields?
Is it a bug, or I am doing something wrong?
- duplicates
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- Closed
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