Hi! As part of a PoC, I did some experimentation on a very simple local cluster (sharded, two nodes with some zones contraints). Everything’s going fine, but I’ve got a gap between my experiment and the documentation concerning sharded views. The documentation (6.0+) states:
Views are considered sharded if their underlying collection is sharded. You cannot specify a sharded view for the
fromfield in$lookupand$graphLookupoperations.
However, it works perfectly on my test example (a sharded collection groups and a simple view groupsView that only contains a sort stage).
I was wondering if this was an omission linked to 5.1 release, which allows to use sharded collections from lookup and graphlookup? Or maybe my test case is too simplistic? If I can provide you with more details, please don’t hesitate to ask.
MongoDB version: 6.0.5
Sharded view:
db.createView(
"groupsView",
"groups",
[{ $sort: { name: 1 } }]
)
Execution stats :
{
"serverInfo" : {
"host" : "b68e294df2ba",
"port" : 27017.0,
"version" : "6.0.5",
"gitVersion" : "c9a99c120371d4d4c52cbb15dac34a36ce8d3b1d"
},
"serverParameters" : {
"internalQueryFacetBufferSizeBytes" : 104857600.0,
"internalQueryFacetMaxOutputDocSizeBytes" : 104857600.0,
"internalLookupStageIntermediateDocumentMaxSizeBytes" : 104857600.0,
"internalDocumentSourceGroupMaxMemoryBytes" : 104857600.0,
"internalQueryMaxBlockingSortMemoryUsageBytes" : 104857600.0,
"internalQueryProhibitBlockingMergeOnMongoS" : 0.0,
"internalQueryMaxAddToSetBytes" : 104857600.0,
"internalDocumentSourceSetWindowFieldsMaxMemoryBytes" : 104857600.0
},
"mergeType" : "mongos",
"splitPipeline" : {
"shardsPart" : [
{
"$graphLookup" : {
"from" : "groupsView",
"as" : "toto",
"connectToField" : "group_index",
"connectFromField" : "group_index",
"startWith" : "$group_index"
}
}
],
"mergerPart" : [
{
"$mergeCursors" : {
"lsid" : {
"id" : "e3671c9d-6a7b-4c22-9d53-8708bd4a1299",
"uid" : "47DEQpj8HBSa+/TImW+5JCeuQeRkm5NM.. 8 more bytes"
},
"compareWholeSortKey" : false,
"tailableMode" : "normal",
"nss" : "pocDB.groups",
"allowPartialResults" : false,
"recordRemoteOpWaitTime" : false
}
}
]
},
"shards" : {
"rs-shard-eu-frc-2" : {
"host" : "mongodb-shard-eu-frc-2-001:27017",
"stages" : [
{
"$cursor" : {
"queryPlanner" : {
"namespace" : "pocDB.groups",
"indexFilterSet" : false,
"parsedQuery" : {
},
"queryHash" : "17830885",
"planCacheKey" : "17830885",
"maxIndexedOrSolutionsReached" : false,
"maxIndexedAndSolutionsReached" : false,
"maxScansToExplodeReached" : false,
"winningPlan" : {
"stage" : "SHARDING_FILTER",
"inputStage" : {
"stage" : "COLLSCAN",
"direction" : "forward"
}
},
"rejectedPlans" : [
]
},
"executionStats" : {
"executionSuccess" : true,
"nReturned" : 10000.0,
"executionTimeMillis" : 24023.0,
"totalKeysExamined" : 0.0,
"totalDocsExamined" : 10000.0,
"executionStages" : {
"stage" : "SHARDING_FILTER",
"nReturned" : 10000.0,
"executionTimeMillisEstimate" : 1.0,
"works" : 10002.0,
"advanced" : 10000.0,
"needTime" : 1.0,
"needYield" : 0.0,
"saveState" : 11.0,
"restoreState" : 11.0,
"isEOF" : 1.0,
"chunkSkips" : 0.0,
"inputStage" : {
"stage" : "COLLSCAN",
"nReturned" : 10000.0,
"executionTimeMillisEstimate" : 1.0,
"works" : 10002.0,
"advanced" : 10000.0,
"needTime" : 1.0,
"needYield" : 0.0,
"saveState" : 11.0,
"restoreState" : 11.0,
"isEOF" : 1.0,
"direction" : "forward",
"docsExamined" : 10000.0
}
}
}
},
"nReturned" : 10000,
"executionTimeMillisEstimate" : 17
},
{
"$graphLookup" : {
"from" : "groupsView",
"as" : "toto",
"connectToField" : "group_index",
"connectFromField" : "group_index",
"startWith" : "$group_index"
},
"nReturned" : 10000,
"executionTimeMillisEstimate" : 24024
}
]
}
},
"command" : {
"aggregate" : "groups",
"pipeline" : [
{
"$graphLookup" : {
"from" : "groupsView",
"startWith" : "$group_index",
"connectFromField" : "group_index",
"connectToField" : "group_index",
"as" : "toto"
}
}
],
"cursor" : {
}
},
"ok" : 1.0,
"$clusterTime" : {
"clusterTime" : "2023-06-05T09:08:26.000+0000",
"signature" : {
"hash" : "AAAAAAAAAAAAAAAAAAAAAAAAAAA=",
"keyId" : 0
}
},
"operationTime" : "2023-06-05T09:08:26.000+0000"
}