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https://issues.apache.org/jira/browse/KUDU-3453?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Alexey Serbin updated KUDU-3453:
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    Summary: Fine-grained anchoring for WAL segments for tablet copy  (was: 
Fine-grained anchoring for WAL segments during tablet copying)

> Fine-grained anchoring for WAL segments for tablet copy
> -------------------------------------------------------
>
>                 Key: KUDU-3453
>                 URL: https://issues.apache.org/jira/browse/KUDU-3453
>             Project: Kudu
>          Issue Type: Improvement
>          Components: tablet, tserver
>            Reporter: Alexey Serbin
>            Priority: Major
>
> Tablet copying is a provision to implement the process of automatic tablet 
> re-replication in Kudu.  When the system catalog (Kudu master) detects that a 
> tablet replica is no longer available, it automatically re-replicates a 
> tablet to a destination tablet server using another healthy tablet replica in 
> the cluster as the source.
> When copying a tablet from one tablet server to another, the source tablet 
> copying session "anchors" WAL segments to be transfered to the destination 
> server, so they are not GC-ed by the tablet maintenance operation when they 
> are no longer needed locally, but the tablet copy session is still in 
> progress.
> The anchored WAL segments are releases all at once when the tablet copying 
> session completes with success of failure.  However, there might be long 
> running tablet copying sessions, and with high data ingest rate, the source 
> tablet replica might accumulate huge amount of WAL data which isn't relevant 
> at both the source and the destination server.
> To prevent accumulation of WAL data for long-running tablet copying sessions, 
> it's necessary to update the WAL anchors in a more granular manner, e.g. 
> un-anchor a segment once it has been successfully copied and persisted by the 
> client tablet copying session.



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