danny0405 commented on code in PR #9291:
URL: https://github.com/apache/hudi/pull/9291#discussion_r1275646230


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website/docs/timeline.md:
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@@ -39,4 +44,36 @@ organization reflects the actual time or `event time`, the 
data was intended for
 
 When there is late arriving data (data intended for 9:00 arriving >1 hr late 
at 10:20), we can see the upsert producing new data into even older time 
buckets/folders.
 With the help of the timeline, an incremental query attempting to get all new 
data that was committed successfully since 10:00 hours, is able to very 
efficiently consume
-only the changed files without say scanning all the time buckets > 07:00.
\ No newline at end of file
+only the changed files without say scanning all the time buckets > 07:00.
+
+### Active and Archived timeline
+Hudi divides the entire timeline into active and archived timeline. As the 
name suggests active timeline is consulted all
+the time to serve metadata on valid data files and to ensure reads on the 
timeline does not incur unnecessary latencies 
+as timeline grows, the active timeline needs to be bounded on the metadata 
(timeline instants) it can serve. To ensure this, 
+after certain thresholds the archival kicks in to move older timeline events 
to the archived timeline. In general, archival 
+timeline is never contacted for regular operations of the table and is merely 
used for book-keeping and debugging purposes.

Review Comment:
   We are rebuilding the archived timeline stuff, it could served for more 
frequent queries by the writer/readers. Should be fine we put it like this in 
current branch.



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