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SERVER-49602 Architecture guide: Clustered Indexes

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Louis Williams 2021-04-02 13:45:12 -04:00 committed by Evergreen Agent
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src/mongo/db/catalog/README.md
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@ -1718,6 +1718,27 @@ schema, per returned document:
} }
``` ```
# Time-series Collections
## Clustered Collections
Collections clustered by _id store documents in _id-order on the RecordStore. Unlike regular
collections, they do not require a separate index from _id values to RecordIds. RecordIDs are
encoded using each document's _id value, rather than a 64-bit integer. Currently, this value must be
an ObjectId.
Clustered collections may be created with the `clusteredIndex` collection creation option, but this
feature is limited to internal time-series buckets collections only.
## TTL Deletions
Like a secondary TTL index, clustered collections can delete old data when created with the
`expireAfterSeconds` collection creation option.
The TTL monitor will only delete data from a time-series bucket collection when a bucket's minimum
time, _id, is past the expiration plus the bucket maximum time span (default 1 hour). This
procedure avoids deleting buckets with data that is not older than the expiration time.
# Glossary # Glossary
**binary comparable**: Two values are binary comparable if the lexicographical order over their byte **binary comparable**: Two values are binary comparable if the lexicographical order over their byte
representation, from lower memory addresses to higher addresses, is the same as the defined ordering representation, from lower memory addresses to higher addresses, is the same as the defined ordering