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From "Jonathan Gray (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HBASE-2376) Add special SnapshotScanner which presents view of all data at some time in the past
Date Thu, 25 Mar 2010 16:01:27 GMT

    [ https://issues.apache.org/jira/browse/HBASE-2376?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12849738#action_12849738
] 

Jonathan Gray commented on HBASE-2376:
--------------------------------------

The initial idea is that we'd introduce a new per-family configuration, something like TTKAV
(Time To Keep All Versions).  This setting would define how far back you would be able to
perform this snapshot.  In practice, it might be something like 1 day or 1 week, but could
be configured.  This setting would ensure that no versions are deleted until outside the TTKAV.
 Once outside that range, the original TTL and MaxVersions settings would be enforced (on
major compactions).

The second piece would be a special SnapshotScanner that took a timestamp and returned data
as it was at that timestamp.  This stamp would of course have to be less than now() and greater
than now() - TTKAV.  It would have the smarts to basically toss out anything with a newer
stamp, including deletes.

The reason for introducing a new parameter is that you must keep all versions of everything
in order to perform the back-in-time snapshot, but you don't want to force constraints on
how you would use the normal maxVersions/TTL parameters to clear out multiple versions of
stuff during major compactions (once outside the snapshotable time window).

> 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: Hadoop HBase
>          Issue Type: New Feature
>          Components: client, regionserver
>    Affects Versions: 0.20.3
>            Reporter: Jonathan Gray
>
> 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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