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Type:
New Feature
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Resolution: Unresolved
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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: None
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Query Optimization
I have seen a number of customer queries use $addToSet in scenarios that it is not necessary for and is in fact a bad choice due to it's materialization of a giant array. For example:
[
{
"$match": {
"myField.target": "TARGET"
}
},
{
"$group": {
"_id": {},
"value": {
"$addToSet": "$metadata.something_id"
}
}
},
{
"$project": {
"_id": 0,
"value": {
"$size": "$value"
}
}
}
]
This query only needs the size of the resulting "value" array, so could be re-written like so:
[
{
"$match": {
"metadata.target": "cloud"
}
},
{
"$group": {
"_id": "$metadata.something_id"
}
},
{
"$group": {
"_id": {},
value: {$sum: 1}
}
},
{
"$project": {
"_id": 0
}
}
]
- related to
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- Backlog
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