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https://issues.apache.org/jira/browse/HBASE-2376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13501710#comment-13501710
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Lars Hofhansl commented on HBASE-2376:
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MIN_VERSIONS affects expired KVs. It's means: "You can expire KVs after this
TTL, but keep at least MIN_VERSIONS versions around".
I was going to Jonathan's initial description:
bq. TTKAV (Time To Keep All Versions) This setting would define how far back
you would be able to perform this snapshot.
You'd do that by setting MAX_VERSIONS to MAX_LONG, TTL to the flashback time,
and MIN_VERSIONS to the number of version you want keep around. Now within the
TTL you'd keep all versions, outside of the TTL MIN_VERSIONS versions are kept.
But I see now. So the snapshot scanner is special in that only through this
specific scanner you can look further back than the TTL.
This does seem a pretty esoteric feature then, though.
Flashback only makes sense together with TTL (otherwise you could set the TTL).
You have a TTL and a sort of a super TTL for which you can only use a special
scanner.
> Add special SnapshotScanner which presents view of all data at some time in
> the past
> ------------------------------------------------------------------------------------
>
> Key: HBASE-2376
> URL: https://issues.apache.org/jira/browse/HBASE-2376
> Project: HBase
> Issue Type: New Feature
> Components: Client, regionserver
> Affects Versions: 0.20.3
> Reporter: Jonathan Gray
> Assignee: Pritam Damania
>
> In order to support a particular kind of database "snapshot" feature which
> doesn't require copying data, we came up with the idea for a special
> SnapshotScanner that would present a view of your data at some point in the
> past. The primary use case for this would be to be able to recover
> particular data/rows (but not all data, like a global rollback) should they
> have somehow been messed up (application fault, application bug, user error,
> etc.).
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