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Type:
Bug
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Resolution: Gone away
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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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None
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Query Execution
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ALL
SERVER-84488 delivered a new method buildBlockAccumulatorSum() that injected some bugs. It also does not make $sum work in block processing mode (though the ticket was officially about making $count work in block processing mode, so maybe that bit was expected).
Reproduction (requires featureFlagSbeFull)
These repros are from master branch SHA f726b6db from 2024-03-01, which is four commits after SERVER-84488's commit d2663eca, also from 2024-03-01, that injected the issues.
0. Setup
db.coll.drop()
db.createCollection("coll", {timeseries: {timeField: "t"}})
db.coll.insert({t: new Date(), a: 4, b: 7, c: 5})
db.coll.insert({t: new Date(), a: 2, b: 9, c: 8})
db.coll.insert({t: new Date(), a: 3, b: 1, c: 6})
1. {$sum: "$a"} does NOT use block processing mode, because buildBlockAccumulatorSum() returns an empty vector unless the argument to $sum is a constant. Thus the caller falls back to the existing row-based $sum accumulator and gets the correct answer, but it may be a bug that it did not use block processing mode:
> db.coll.aggregate([{$project: {a: 1}},
{$group: {_id: null, x: {$sum : "$a"}}}], {allowDiskUse: false})
{ "_id" : null, "x" : 9 }
2. {$sum: 10} DOES use block processing mode, but gives wrong results (the sum of three 10s should be 30 but comes out as 10):
> db.coll.aggregate([{$project: {a: 1}},
{$group: {_id: null, x: {$sum : 10}}}], {allowDiskUse: false})
{ "_id" : null, "x" : 10 }
3. {$sum: "10"} (arg is a non-numeric constant) DOES use block processing mode but results in the server core dumping in the SBE VM:
> db.coll.aggregate([{$project: {a: 1}},
{$group: {_id: null, x: {$sum : "10"}}}], {allowDiskUse: false})
Error: network error while attempting to run command 'aggregate' on host '127.0.0.1:27017' :: caused by :: dbclient error communicating with server 127.0.0.1:27017 :: caused by :: futurize :: caused by :: Connection closed by peer :
Mongo.prototype.runCommand@src/mongo/shell/mongo.js:163:17
runClientFunctionWithRetries@src/mongo/shell/session.js:348:42
runCommand@src/mongo/shell/session.js:465:53
DB.prototype._runCommandImpl@src/mongo/shell/db.js:163:45
DB.prototype.runCommand@src/mongo/shell/db.js:178:21
DB.prototype.runReadCommand@src/mongo/shell/db.js:157:17
DB.prototype._runAggregate@src/mongo/shell/db.js:264:22
DBCollection.prototype.aggregate@src/mongo/shell/collection.js:985:21
@(shell):1:9
- is depended on by
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SERVER-87420 Temporarily disable block hashagg
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- Closed
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