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From "James Taylor (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11292) Add an "undelete" operation
Date Tue, 03 Jun 2014 17:36:02 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14016905#comment-14016905
] 

James Taylor commented on HBASE-11292:
--------------------------------------

+1 for this new operation as it will help in the implementation of transactions. Would every
*type* of Delete need a corresponding Undelete?

When KEEP_DELETED_CELLS is on, assume:
- Put is done at t1
- Delete is done at t5
- Undelete is done at t7

If a client does a read at t6, the Delete would be in effect, while if a client does a read
at t8, the Delete would not be in effect. Is that how it'd work?

> Add an "undelete" operation
> ---------------------------
>
>                 Key: HBASE-11292
>                 URL: https://issues.apache.org/jira/browse/HBASE-11292
>             Project: HBase
>          Issue Type: New Feature
>          Components: Deletes
>            Reporter: Gary Helmling
>              Labels: Phoenix
>
> While column families can be configured to keep deleted cells (allowing time range queries
to still retrieve those cells), deletes are still somewhat unique in that they are irreversible
operations.  Once a delete has been issued on a cell, the only way to "undelete" it is to
rewrite the data with a timestamp newer than the delete.
> The idea here is to add an "undelete" operation, that would make it possible to cancel
a previous delete.  An undelete operation will be similar to a delete, in that it will be
written as a marker ("tombstone" doesn't seem like the right word).  The undelete marker,
however, will sort prior to a delete marker, canceling the effect of any following delete.
> In the absence of a column family configured to KEEP_DELETED_CELLS, we can't be sure
if a prior delete marker and the effected cells have already been garbage collected.  In this
case (column family not configured with KEEP_DELETED_CELLS) it may be necessary for the server
to reject undelete operations to avoid creating the appearance of a client contact for undeletes
that can't reliably be honored.
> I think there are additional subtleties of the implementation to be worked out, but I'm
also interested in a broader discussion of interest in this capability.



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