Collscan on Browsing a Collection

[Xeroxxx]

I've the problem that when I open a large collection (~10.000.000 Obj, 22kb Avg, 100GB).

I takes ages to load and I can see a COLLSCAN of _id in the logs.

mongo-1          | {"t":{"$date":"2024-04-20T23:47:40.771+00:00"},"s":"I",  "c":"COMMAND",  "id":51803,   "ctx":"conn26","msg":"Slow query","attr":{"type":"command","ns":"xxx.xxx",
"command":{"aggregate":"xxx","pipeline":[{"$match":{}},{"$group":{"_id":1,"n":{"$sum":1}}}],"cursor":{},"lsid":{"id":{"$uuid":"2b51c014-62f7-49d0-8279-979a8dfa868d"}},"$db":"poedata"},
"planSummary":"COLLSCAN","planningTimeMicros":166,"keysExamined":0,"docsExamined":9343804,"fromPlanCache":true,"cursorExhausted":true,"numYields":47869,"nreturned":1,"queryHash":"366C3F12","planCacheKey":"58CF6002","queryFramework":"sbe","reslen":128,"locks":{"FeatureCompatibilityVersion":{"acquireCount":{"r":47870}},"Global":{"acquireCount":{"r":47870}}},"storage":{"data":{"bytesRead":215941107656,"timeReadingMicros":641289510},"timeWaitingMicros":{"cache":588}},"cpuNanos":351818832796,"remote":"172.18.0.3:46260","protocol":"op_msg","durationMillis":861631}}

The extracted query of mongo express is an aggregate on:

{"$match":{}},{"$group":{"_id":1,"n":{"$sum":1}}}

Replacing the match with for ex sort uses the _id index and then its fast.

Can anyone explain why the Index is not used for browsing a collection and why the index is not used for _id?

[xTudoS]

Are you using the master version or 1.0.2 ?

[Xeroxxx]

Are you using the master version or 1.0.2 ?

I'm using latest docker image: https://hub.docker.com/_/mongo-express

Its tagged as 1.0.2-20

[xTudoS]

Are you using the master version or 1.0.2 ?

I'm using latest docker image: https://hub.docker.com/_/mongo-express

Its tagged as 1.0.2-20

try to build and use your own mongo-express image from master
use this repo to it: https://github.com/mongo-express/mongo-express-docker

official docker image is out-of-date

[Xeroxxx]

Master branch does not change the behavior.

I remember this was working late 2022 early 2023 or so. Thought is was update releated when I updated from mongo 5 to 6.