[GitHub] [incubator-druid] jihoonson commented on a change in pull request #8173: Add a cluster-wide configuration to force timeChunk lock and add a doc for segment locking

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jihoonson commented on a change in pull request #8173: Add a cluster-wide configuration to force timeChunk lock and add a doc for segment locking
URL: https://github.com/apache/incubator-druid/pull/8173#discussion_r310265674
 
 

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 File path: docs/content/ingestion/locking-and-priority.md
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 @@ -24,30 +24,73 @@ title: "Task Locking & Priority"
 
 # Task Locking & Priority
 
+This document explains the task locking system in Druid. Druid's locking system
+and versioning system are tighly coupled with each other to guarantee the correctness of ingested data.
+
+## Overshadow Relation between Segments
+
+You can run a task to overwrite existing data. The segments created by an overwriting task _overshadows_ existing segments.
+Note that the overshadow relation holds only for the same time chunk and the same data source.
+These overshadowed segments are not considered in query processing to filter out stale data.
 
 Review comment:
   Sounds good. Added a brief description about major and minor versions.

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