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From "Lars Hofhansl (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-11292) Add an "undelete" operation
Date Sat, 26 Jul 2014 21:23:38 GMT

    [ https://issues.apache.org/jira/browse/HBASE-11292?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14075492#comment-14075492
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Lars Hofhansl commented on HBASE-11292:
---------------------------------------

Can we turn this around and implement undelete with redoing the corresponding put and handling
the ambiguities with seq ids?
I've been arguing against this, since it would break idempotency of HBase actions, but on
light of this I might relent :)
I guess it would require to know what exactly the delete affected, which may or may not possible.

Yet another way to look at it is: why undelete at all? Ignoring failed transactions needs
to be implemented anyway, so instead of undo one could just continue to ignore the transaction.

> 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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