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Type:
Improvement
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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: Query Planning
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Query Optimization
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Hi,
I have a time-series collection where I'm keeping the prices of cryptocurrencies for 30 days with the second granularity. Around 2000 cryptocurrency ticker data have been inserted into the time-series collection every one or two seconds. For some reason, I require to retrieve the distinct symbols. I have more than 2 Billion records in the time-series collection.
When I run the following query, it didn't complete in a few minutes and I had to stop it.
db.cryptoTickerBinance.distinct("symbol")
Available indexes on the collection are listed below:
[
{
"v": 2,
"key": {
"symbol": 1,
"time": 1
},
"name": "symbol_1_time_1"
},
{
"v": 2,
"key": {
"time": 1
},
"name": "time_1"
},
{
"v": 2,
"key": {
"symbol": 1,
"time": -1
},
"name": "sym2"
},
{
"v": 2,
"key": {
"time": -1
},
"name": "time_2"
}
]
However, when I use $group staging it works fast as expected since it's using DISTINCT_SCAN step.
db.cryptoTickerBinance.aggregate([
{
'$group': {
'_id': '$symbol'
}
}
]).explain('executionStats')
{ explainVersion: '1',
stages:
[ { '$cursor':
{ queryPlanner:
{ namespace: 'exchange.system.buckets.cryptoTickerBinance',
indexFilterSet: false,
parsedQuery: {},
queryHash: 'A855245D',
planCacheKey: 'A855245D',
maxIndexedOrSolutionsReached: false,
maxIndexedAndSolutionsReached: false,
maxScansToExplodeReached: false,
winningPlan:
{ stage: 'PROJECTION_COVERED',
transformBy: { meta: 1, _id: 0 },
inputStage:
{ stage: 'DISTINCT_SCAN',
keyPattern: { meta: 1, 'control.min.time': 1, 'control.max.time': 1 },
indexName: 'symbol_1_time_1',
isMultiKey: false,
multiKeyPaths: { meta: [], 'control.min.time': [], 'control.max.time': [] },
isUnique: false,
isSparse: false,
isPartial: false,
indexVersion: 2,
direction: 'forward',
indexBounds:
{ meta: [ '[MinKey, MaxKey]' ],
'control.min.time': [ '[MinKey, MaxKey]' ],
'control.max.time': [ '[MinKey, MaxKey]' ] } } },
rejectedPlans: [] },
executionStats:
{ executionSuccess: true,
nReturned: 2080,
executionTimeMillis: 52,
totalKeysExamined: 2080,
totalDocsExamined: 0,
executionStages:
{ stage: 'PROJECTION_COVERED',
nReturned: 2080,
executionTimeMillisEstimate: 49,
works: 2081,
advanced: 2080,
needTime: 0,
needYield: 0,
saveState: 4,
restoreState: 4,
isEOF: 1,
transformBy: { meta: 1, _id: 0 },
inputStage:
{ stage: 'DISTINCT_SCAN',
nReturned: 2080,
executionTimeMillisEstimate: 49,
works: 2081,
advanced: 2080,
needTime: 0,
needYield: 0,
saveState: 4,
restoreState: 4,
isEOF: 1,
keyPattern: { meta: 1, 'control.min.time': 1, 'control.max.time': 1 },
indexName: 'symbol_1_time_1',
isMultiKey: false,
multiKeyPaths: { meta: [], 'control.min.time': [], 'control.max.time': [] },
isUnique: false,
isSparse: false,
isPartial: false,
indexVersion: 2,
direction: 'forward',
indexBounds:
{ meta: [ '[MinKey, MaxKey]' ],
'control.min.time': [ '[MinKey, MaxKey]' ],
'control.max.time': [ '[MinKey, MaxKey]' ] },
keysExamined: 2080 } } } },
nReturned: 2080,
executionTimeMillisEstimate: 49 },
{ '$groupByDistinctScan': { newRoot: { _id: '$meta' } },
nReturned: 2080,
executionTimeMillisEstimate: 49 } ],
serverInfo:
{ host: 'atlas-3uvq7m-shard-00-02.iubjy.mongodb.net',
port: 27017,
version: '6.0.0',
gitVersion: 'e61bf27c2f6a83fed36e5a13c008a32d563babe2' },
serverParameters:
{ internalQueryFacetBufferSizeBytes: 104857600,
internalQueryFacetMaxOutputDocSizeBytes: 104857600,
internalLookupStageIntermediateDocumentMaxSizeBytes: 104857600,
internalDocumentSourceGroupMaxMemoryBytes: 104857600,
internalQueryMaxBlockingSortMemoryUsageBytes: 104857600,
internalQueryProhibitBlockingMergeOnMongoS: 0,
internalQueryMaxAddToSetBytes: 104857600,
internalDocumentSourceSetWindowFieldsMaxMemoryBytes: 104857600 },
command:
{ aggregate: 'system.buckets.cryptoTickerBinance',
pipeline:
[ { '$_internalUnpackBucket':
{ timeField: 'time',
metaField: 'symbol',
bucketMaxSpanSeconds: 3600,
assumeNoMixedSchemaData: true } },
{ '$group': { _id: '$symbol' } } ],
cursor: {},
collation: { locale: 'simple' } },
ok: 1,
'$clusterTime':
{ clusterTime: Timestamp({ t: 1659631070, i: 2089 }),
signature:
{ hash: Binary(Buffer.from("d16b946bcb75e6999bd12f47bf93c85c1bab16ea", "hex"), 0),
keyId: 7079845501138373000 } },
operationTime: Timestamp({ t: 1659631070, i: 2089 }) }
How the distinct() query can be optimized on time-series collections? It may be linked to another ticket (https://jira.mongodb.org/browse/SERVER-14227).
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