# Side bucket catalog > Source-anchored research for Side bucket catalog. Run status: COMPLETED. Parent: [Bucket catalog memory and closure reasons](https://llms-explorer.com/tree/bucket-catalog-memory-and-closure-reasons/) · 2 facets · 8 facts · page: https://llms-explorer.com/tree/side-bucket-catalog/ ## How it works - Alibaba Cloud’s July 2025 engine-parameter release notes list exposure of timeseriesSideBucketCatalogMemoryUsageThreshold for its MongoDB 8.0 service; this is a managed-service availability date, not evidence that upstream MongoDB introduced the mechanism in July 2025. (low confidence) — [source](https://help.aliyun.com/en/mongodb/product-overview/engine-release-notes) - The parameter defines when idle-bucket expiry begins; treating it as a guaranteed ceiling on total mongod memory is unsupported by these interfaces and the regression test. (medium confidence) — [source](https://github.com/mongodb/mongo/blob/35647d07bc4bc11966c90fe7100eb1db0b0ac1d9/src/mongo/db/timeseries/timeseries.idl) ## Facts and statements - At MongoDB revision 35647d07bc4bc11966c90fe7100eb1db0b0ac1d9, timeseriesSideBucketCatalogMemoryUsageThreshold is a byte threshold above which idle buckets in the side bucket catalog are expired; Alibaba Cloud documents the same threshold semantics. (medium confidence) — [source](https://github.com/mongodb/mongo/blob/35647d07bc4bc11966c90fe7100eb1db0b0ac1d9/src/mongo/db/timeseries/timeseries.idl) - At MongoDB commit 35647d07, timeseriesSideBucketCatalogMemoryUsageThreshold is expressed in bytes and defaults to 104857600 bytes (100 MiB); the ApsaraDB MongoDB 8.0 parameter table independently lists the same numeric default. (high confidence) — [source](https://github.com/mongodb/mongo/blob/35647d07bc4bc11966c90fe7100eb1db0b0ac1d9/src/mongo/db/timeseries/timeseries.idl) - The pinned parameter definition allows startup and runtime configuration. MongoDB’s regression test at revision 46e8db22 exercises both configuration modes. (high confidence) — [source](https://github.com/mongodb/mongo/blob/35647d07bc4bc11966c90fe7100eb1db0b0ac1d9/src/mongo/db/timeseries/timeseries.idl) - The side catalog has a separate idle-bucket-expiry memory threshold, timeseriesSideBucketCatalogMemoryUsageThreshold; the regression test isolates it by configuring 1 MiB for the side catalog and 100 MiB for the main catalog. (high confidence) — [source](https://github.com/mongodb/mongo/blob/35647d07bc4bc11966c90fe7100eb1db0b0ac1d9/src/mongo/db/timeseries/timeseries.idl) - The regression test at revision 46e8db22 expects numBucketsArchivedDueToMemoryThreshold to increase after it induces side-catalog memory pressure; its comments allow subsequent closure if archival does not reclaim enough memory, and it checks that memory-triggered closures do not outnumber memory-triggered archivals. (low confidence) — [source](https://github.com/mongodb/mongo/blob/46e8db22d75751f6469d95f87a5ad700f51264d6/jstests/noPassthrough/timeseries/timeseries_side_bucket_catalog_memory_usage_threshold.js) - The BucketCatalog header provides getSideBucketCatalogCollectionStats and documents that it assumes statistics for one collection; it also declares mergeExecutionStatsToBucketCatalog for merging collection execution statistics. (low confidence) (verified as of 2026-10-24) — [source](https://github.com/mongodb/mongo/blob/master/src/mongo/db/timeseries/bucket_catalog/bucket_catalog.h)