please read comment and first answer. question is solved.
https://mongoplayground.net/p/J1Hs5RKu39G
I need help interpreting the explain output. I can see that the index is used. However, I am still not sure whether the $sort, $skip, and $limit stages will be done in memory, ie be blocking and subjected to the 100MB limit. Note that the query contains 2 $or in the $match stage. And of course, there is the $regex. So when all of that is combined in one query, I am sure what will happen.
How can I tell from the explain whether or not the $sort, $skip, and $limit stages will be done in memory, ie be blocking and subjected to the 100MB limit?
schema and index:
[
{
"collection": "collection",
"count": 100,
"content": {
"name": {
"type": "enum",
"values": [
"a",
"b",
"c",
"d",
"e"
]
},
"name_1": {
"type": "enum",
"values": [
"a",
"b",
"c",
"d",
"e"
]
},
"utc": {
"type": "enum",
"values": [
1,
2,
3,
4,
5,
6,
7,
8,
9
]
},
"description": {
"type": "enum",
"values": [
"Coffee and cakes",
"Gourmet hamburgers",
"Just coffee",
"Discount clothing",
"Indonesian goods"
]
},
"description_2": {
"type": "enum",
"values": [
"Coffee and cakes",
"Gourmet hamburgers",
"Just coffee",
"Discount clothing",
"Indonesian goods"
]
}
},
"indexes": [
{
"name": "description_text_idx",
"key": {
"name": 1,
"utc": 1,
"description": 1
}
},
{
"name": "description_text_idx_2",
"key": {
"name": 1,
"utc": 1,
"description_2": 1
}
},
{
"name": "description_text_idx_3",
"key": {
"name_1": 1,
"utc": 1,
"description": 1
}
},
{
"name": "description_text_idx_4",
"key": {
"name_1": 1,
"utc": 1,
"description_2": 1
}
}
]
}
]
query:
db.collection.aggregate([
{
$match: {
$and: [
{
$or: [
{
name: "a"
},
{
name_1: "b"
}
]
},
{
$or: [
{
description: {
$regex: "and"
}
},
{
description_2: {
$regex: "goo"
}
}
]
}
]
}
},
{
$sort: {
timestamp_utc: -1
}
},
{
$skip: 10
},
{
$limit: 100
}
]).explain()
explain:
{
"$clusterTime": {
"clusterTime": Timestamp(1696816196, 105),
"signature": {
"hash": BinData(0, "tmzq2+QI7fODnvWyR/eC3yfzclA="),
"keyId": NumberLong(7230504570105888773)
}
},
"command": {
"$db": "49da1669e4de3fc843aebffc2dc28e0e",
"aggregate": "collection",
"cursor": {
"batchSize": 1000
},
"maxTimeMS": NumberLong(20000),
"pipeline": [
{
"$match": {
"$and": [
{
"$or": [
{
"name": "a"
},
{
"name_1": "b"
}
]
},
{
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
}
]
}
},
{
"$sort": {
"timestamp_utc": -1
}
},
{
"$skip": 10
},
{
"$limit": 100
}
]
},
"explainVersion": "1",
"operationTime": Timestamp(1696816196, 105),
"queryPlanner": {
"indexFilterSet": false,
"maxIndexedAndSolutionsReached": false,
"maxIndexedOrSolutionsReached": false,
"maxScansToExplodeReached": false,
"namespace": "49da1669e4de3fc843aebffc2dc28e0e.collection",
"optimizedPipeline": true,
"parsedQuery": {
"$and": [
{
"$or": [
{
"name": {
"$eq": "a"
}
},
{
"name_1": {
"$eq": "b"
}
}
]
},
{
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
}
]
},
"planCacheKey": "CB15319B",
"queryHash": "30C8890A",
"rejectedPlans": [
{
"inputStage": {
"inputStage": {
"filter": {
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
},
"inputStage": {
"inputStages": [
{
"direction": "forward",
"indexBounds": {
"description_2": [
"[MinKey, MaxKey]"
],
"name": [
"[\"a\", \"a\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_2",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description_2": 1,
"name": 1,
"utc": 1
},
"multiKeyPaths": {
"description_2": [],
"name": [],
"utc": []
},
"stage": "IXSCAN"
},
{
"direction": "forward",
"indexBounds": {
"description": [
"[MinKey, MaxKey]"
],
"name_1": [
"[\"b\", \"b\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_3",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description": 1,
"name_1": 1,
"utc": 1
},
"multiKeyPaths": {
"description": [],
"name_1": [],
"utc": []
},
"stage": "IXSCAN"
}
],
"stage": "OR"
},
"stage": "FETCH"
},
"limitAmount": 110,
"memLimit": 104857600,
"sortPattern": {
"timestamp_utc": -1
},
"stage": "SORT",
"type": "simple"
},
"skipAmount": 0,
"stage": "SKIP"
},
{
"inputStage": {
"inputStage": {
"filter": {
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
},
"inputStage": {
"inputStages": [
{
"direction": "forward",
"indexBounds": {
"description": [
"[MinKey, MaxKey]"
],
"name": [
"[\"a\", \"a\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description": 1,
"name": 1,
"utc": 1
},
"multiKeyPaths": {
"description": [],
"name": [],
"utc": []
},
"stage": "IXSCAN"
},
{
"direction": "forward",
"indexBounds": {
"description_2": [
"[MinKey, MaxKey]"
],
"name_1": [
"[\"b\", \"b\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_4",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description_2": 1,
"name_1": 1,
"utc": 1
},
"multiKeyPaths": {
"description_2": [],
"name_1": [],
"utc": []
},
"stage": "IXSCAN"
}
],
"stage": "OR"
},
"stage": "FETCH"
},
"limitAmount": 110,
"memLimit": 104857600,
"sortPattern": {
"timestamp_utc": -1
},
"stage": "SORT",
"type": "simple"
},
"skipAmount": 0,
"stage": "SKIP"
},
{
"inputStage": {
"inputStage": {
"filter": {
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
},
"inputStage": {
"inputStages": [
{
"direction": "forward",
"indexBounds": {
"description_2": [
"[MinKey, MaxKey]"
],
"name": [
"[\"a\", \"a\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_2",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description_2": 1,
"name": 1,
"utc": 1
},
"multiKeyPaths": {
"description_2": [],
"name": [],
"utc": []
},
"stage": "IXSCAN"
},
{
"direction": "forward",
"indexBounds": {
"description_2": [
"[MinKey, MaxKey]"
],
"name_1": [
"[\"b\", \"b\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_4",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description_2": 1,
"name_1": 1,
"utc": 1
},
"multiKeyPaths": {
"description_2": [],
"name_1": [],
"utc": []
},
"stage": "IXSCAN"
}
],
"stage": "OR"
},
"stage": "FETCH"
},
"limitAmount": 110,
"memLimit": 104857600,
"sortPattern": {
"timestamp_utc": -1
},
"stage": "SORT",
"type": "simple"
},
"skipAmount": 0,
"stage": "SKIP"
}
],
"winningPlan": {
"inputStage": {
"inputStage": {
"filter": {
"$or": [
{
"description": {
"$regex": "and"
}
},
{
"description_2": {
"$regex": "goo"
}
}
]
},
"inputStage": {
"inputStages": [
{
"direction": "forward",
"indexBounds": {
"description": [
"[MinKey, MaxKey]"
],
"name": [
"[\"a\", \"a\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description": 1,
"name": 1,
"utc": 1
},
"multiKeyPaths": {
"description": [],
"name": [],
"utc": []
},
"stage": "IXSCAN"
},
{
"direction": "forward",
"indexBounds": {
"description": [
"[MinKey, MaxKey]"
],
"name_1": [
"[\"b\", \"b\"]"
],
"utc": [
"[MinKey, MaxKey]"
]
},
"indexName": "description_text_idx_3",
"indexVersion": 2,
"isMultiKey": false,
"isPartial": false,
"isSparse": false,
"isUnique": false,
"keyPattern": {
"description": 1,
"name_1": 1,
"utc": 1
},
"multiKeyPaths": {
"description": [],
"name_1": [],
"utc": []
},
"stage": "IXSCAN"
}
],
"stage": "OR"
},
"stage": "FETCH"
},
"limitAmount": 110,
"memLimit": 104857600,
"sortPattern": {
"timestamp_utc": -1
},
"stage": "SORT",
"type": "simple"
},
"skipAmount": 0,
"stage": "SKIP"
}
},
"serverParameters": {
"internalDocumentSourceGroupMaxMemoryBytes": 104857600,
"internalDocumentSourceSetWindowFieldsMaxMemoryBytes": 104857600,
"internalLookupStageIntermediateDocumentMaxSizeBytes": 104857600,
"internalQueryFacetBufferSizeBytes": 104857600,
"internalQueryFacetMaxOutputDocSizeBytes": 104857600,
"internalQueryMaxAddToSetBytes": 104857600,
"internalQueryMaxBlockingSortMemoryUsageBytes": 104857600,
"internalQueryProhibitBlockingMergeOnMongoS": 0
}
}
You can tell it from this part:
"stage": "FETCH"
},
"limitAmount": 110,
"memLimit": 104857600,
"sortPattern": {
"timestamp_utc": -1
},
"stage": "SORT",
"type": "simple"
},
"skipAmount": 0,
"stage": "SKIP"
}
SORT indicates in-memory blocking sort.
memLimit on FETCH stage is the 100MB limit.