Operational Defect Database
BugZero found this defect 39 days ago.
Data sources
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MongoDB | 2638273
cache pressure causes one bucket per single document with time series collections
Last update date:
4/11/2024
Affected products:
MongoDB Server
Affected releases:
7.0.4
7.0.5
Fixed releases:
No fixed releases provided.
Description:
Info
A while (several days usually) after starting up the database (sharded cluster), newly inserted time series collection will have exactly (as far as I personally observed) as many buckets as documents, regardless of granularity or metafield settings. The stats() command shows that the buckets were closed due to cache pressure (numBucketsClosedDueToCachePressure). I also experience the issue with after deleting a time series collection, and inserting either the same or other collections. This behavior has also been documented/observed in: https://www.mongodb.com/community/forums/t/suboptimal-bucket-creation-in-timeseries-collection-due-to-cache-pressure/249863 https://dba.stackexchange.com/questions/336013/mongodb-timeseries-data-at-high-load-causes-cache-pressure-in-time https://www.mongodb.com/community/forums/t/why-timeseries-bucket-count-is-different-on-2-independent-environment-with-same-data/265066/
Top User Comments
JIRAUSER1265262 commented on Thu, 11 Apr 2024 01:16:44 +0000: Hi zongli@amzracing.ch, Thanks for your report. In order to proceed, would you please archive (tar or zip) the mongod.log files and the $dbpath/diagnostic.data directory (the contents are described here) and upload them to this support uploader location? Files uploaded to this portal are visible only to MongoDB employees and are routinely deleted after some time. To give more context around our investigation, please also provide: A clear description of the nature if your insert/delete workload (such as a sample document, number of documents) Clear timestamp of when the offending workload begins Clear timestamp of when you observe an articulable issue with the workload Chris
Steps to Reproduce
In a sharded mongodb cluster (in my case 7.0.4). Insert time-series collection into a sharded database. Either keep inserting, or in my case, delete the one, and re-insert the same time-series collection. The bucket count equals the document count.
