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https://issues.apache.org/jira/browse/HBASE-23602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17001165#comment-17001165
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Geoffrey Jacoby commented on HBASE-23602:
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Some potential use cases where this is required for correctness:
1. A change stream producer that shows both new and old versions of a row after
a change (DynamoDB has something similar to this)
2. Guaranteeing that all intermediate values are still present on disk when a
backup tool generates a daily HBase snapshot.
3. Raw consistency verification between two replicated tables both taking
writes.
> TTL Before Which No Data is Purged
> ----------------------------------
>
> Key: HBASE-23602
> URL: https://issues.apache.org/jira/browse/HBASE-23602
> Project: HBase
> Issue Type: New Feature
> Reporter: Geoffrey Jacoby
> Priority: Major
>
> HBase currently offers operators a choice. They can set
> KEEP_DELETED_CELLS=true and VERSIONS to max value, plus no TTL, and they will
> always have a complete history of all changes (but high storage costs and
> penalties to read performance). Or they can have KEEP_DELETED_CELLS=false and
> VERSIONS/TTL set to some reasonable values, but that means that major
> compactions can destroy the ability to do a consistent snapshot read of any
> prior time. (This limits the usefulness and correctness of, for example,
> Phoenix's SCN lookback feature.)
> I propose having a new TTL property to give a minimum age that an expired or
> deleted Cell would have to achieve before it could be purged. (I see that
> HBASE-10118 already does something similar for the delete markers
> themselves.)
> This would allow operators to have a consistent history for some finite
> amount of recent time while still purging out the "long tail" of obsolete /
> deleted versions.
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