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Type:
Bug
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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 Integration
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ALL
Timeseries "last point" queries are those that pick out the most recent event in each series. For example:
{$group: {
_id: "$meta.sensor_id",
last_time: {$top: {sortBy: {time: 1}, output: "$time"}},
last_value: {$top: {sortBy: {time: 1}, output: "$value"}},
}}
We rewrite the query to pick out the latest bucket within each series, before unpacking. This assumes that the latest bucket contains the latest event, which is true when control.max.time is a tight upper bound.
However, for events before 1970 control.max.time is not a tight bound:
> db.createCollection('ts', {timeseries:{timeField:'t',metaField:'m'}}) { "ok" : 1 } > db.ts.insert({t: ISODate('1969-01-01T00:00:12.345')}) WriteResult({ "nInserted" : 1 }) > db.system.buckets.ts.find().pretty() { "_id" : ObjectId("fe1eccbc6f22cc96f1dd557f"), "control" : { "min" : { // Tight lower bound, not rounded. "t" : ISODate("1969-01-01T00:00:12.345Z") }, "max" : { // Rounded upper bound, not tight. "t" : ISODate("1969-01-01T00:01:00Z") } }, "data" : ... }
This means if a series contains only pre-1970 dates, the query can return a wrong event.
A simple / coarse way to fix this would be to disable this rewrite when the collection contains extended-range dates.
- is related to
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- Open
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- Backlog
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- related to
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SERVER-67825 Investigate where time-series functionality relies on control summary timestamps
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- Closed
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