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Type:
Sub-task
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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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Labels:None
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Query Execution
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Fully Compatible
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QE 2024-04-15, QE 2024-04-29, QE 2024-05-13
Classic $group (the document source) uses ValueUnorderedMap which is defined as absl::node_hash_map. If we don't keep pointers into this map, we should look into changing the implementation to use absl::flat_hash_map, since this map requires less heap allocations and indirection.
MongoDB Enterprise > db.bar.aggregate([{$group: {_id: null, total: {$sum: "$a"}}}])
{ "_id" : null, "total" : 26624000 }
Do not see a noticeable speedup in SBE. All the "a" fields are "2". Saw ~4% speedup in classic mode, but this query runs in SBE by default. There may be queries that run in classic by default that could see some speedup?
Here's a group query that runs in classic by default
db.weather.insertMany( [
{
"metadata": { "sensorId": 5578, "type": "temperature" },
"timestamp": ISODate("1990-05-18T00:00:00.000Z"),
"temp": 12
},
{
"metadata": { "sensorId": 5578, "type": "temperature" },
"timestamp": ISODate("2021-05-18T04:00:00.000Z"),
"temp": 11
},
{
"metadata": { "sensorId": 5578, "type": "temperature" },
"timestamp": ISODate("2021-05-18T08:00:00.000Z"),
"temp": 11
},
{
"metadata": { "sensorId": 5578, "type": "temperature" },
"timestamp": ISODate("2021-05-18T12:00:00.000Z"),
"temp": 12
}
] )
db.weather.aggregate( [
{
$densify: {
field: "timestamp",
range: {
step: 1,
unit: "minute",
bounds:[ ISODate("1990-05-18T00:00:00.000Z"), ISODate("2021-05-18T04:00:00.000Z") ]
}
}
},
{
$group: {
_id: {"$dateTrunc":{"date":"$timestamp","unit":"year"}},
count: { $count: { } }
}
}
] )
Need to increase this knob
db.adminCommand({ setParameter: 1, "internalQueryMaxAllowedDensifyDocs": 50000000 })
Takes about 15 seconds, about 3% of which are in hash table try_emplace_back.
|------+----------------+-------| | flat | queryFramework | ms | |------+----------------+-------| | no | classic | 16729 | | no | classic | 16726 | |------+----------------+-------| | yes | classic | 16285 | | yes | classic | 16280 | | yes | classic | 16291 | |------+----------------+-------| | yes | sbe | 16301 | | yes | sbe | 16289 | |------+----------------+-------| | no | classic | 16817 | | no | classic | 16923 | | no | classic | 16918 | |------+----------------+-------| | no | sbe | 16885 | | no | sbe | 16896 | | no | sbe | 16959 | |------+----------------+-------|
