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From Ian Varley <ivar...@salesforce.com>
Subject Re: Efficiently wiping out random data?
Date Wed, 19 Jun 2013 18:28:56 GMT
At least in some cases, the answer to that question ("do you even have to destroy your tapes?")
is a resounding "yes". For some extreme cases (think health care, privacy, etc), companies
do all RDBMS backups to disk instead of tape for that reason. (Transaction logs are considered
different, I guess because they're inherently transient? Who knows.)

The "no time travel" fix doesn't work, because you could still change that code or ACL in
the future and get back to the data. In these cases, one must provably destroy the data.

That said, forcing full compactions (especially if they can be targeted via stripes or levels
or something) is an OK way to handle it, maybe eventually with more ways to nice it down so
it doesn't hose your cluster.


On Jun 19, 2013, at 11:27 AM, Todd Lipcon wrote:

I'd also question what exactly the regulatory requirements for deletion
are. For example, if you had tape backups of your Oracle DB, would you have
to drive to your off-site storage facility, grab every tape you ever made,
and zero out the user's data as well? I doubt it, considering tapes have
basically the same storage characteristics as HDFS in terms of inability to
random write.

Another example: deletes work the same way in most databases -- eg in
postgres, deletion of a record just consists of setting a record's "xmax"
column to the current transaction ID. This is equivalent to a tombstone,
and you have to wait for a VACUUM process to come along and actually delete
the record entry. In Oracle, the record will persist in a rollback segment
for a configurable amount of time, and you can use a Flashback query to
time travel and see it again. In Vertica, you also set an "xmax" entry and
wait until the next merge-out (like a major compaction).

Even in a filesystem, deletion doesn't typically remove data, unless you
use a tool like srm. It just unlinks the inode from the directory tree.

So, if any of the above systems satisfy their use case, then HBase ought to
as well. Perhaps there's an ACL we could add which would allow/disallow
users from doing time travel more than N seconds in the past..  maybe that
would help allay fears?


On Wed, Jun 19, 2013 at 8:12 AM, Jesse Yates <jesse.k.yates@gmail.com<mailto:jesse.k.yates@gmail.com>>wrote:

Chances are that date isn't completely "random". For instance, with a user
they are likely to have an id in their row key, so doing a filtering (with
a custom scanner) major compaction would clean that up. With Sergey's
compaction stuff coming in you could break that out even further and only
have to compact a small set of files to get that removal.

So it's hard, but as its not our direct use case, it's gonna be a few extra

On Wednesday, June 19, 2013, Kevin O'dell wrote:

Yeah, the immutable nature of HDFS is biting us here.

On Wed, Jun 19, 2013 at 8:46 AM, Jean-Daniel Cryans <jdcryans@apache.org<mailto:jdcryans@apache.org>

That sounds like a very effective way for developers to kill clusters
with compactions :)


On Wed, Jun 19, 2013 at 2:39 PM, Kevin O'dell <


  What about adding a flag for the delete, something like -full or
-true(it is early).  Once we issue the delete to the proper
run a flush, then execute a single region major compaction.  That
it is a single record, or a subset of data the impact is minimal.  If
delete happens to hit every region we will compact every region(not
Another thought would be an overwrite, but with versions this logic
becomes more complicated.

On Wed, Jun 19, 2013 at 8:31 AM, Jean-Daniel Cryans <
jdcryans@apache.org<mailto:jdcryans@apache.org> <javascript:;>

Hey devs,

I was presenting at GOTO Amsterdam yesterday and I got a question
about a scenario that I've never thought about before. I'm wondering
what others think.

How do you efficiently wipe out random data in HBase?

For example, you have a website and a user asks you to close their
account and get rid of the data.

Would you say "sure can do, lemme just issue a couple of Deletes!"
call it a day? What if you really have to delete the data, not just
mask it, because of contractual obligations or local laws?

Major compacting is the obvious solution but it seems really
inefficient. Let's say you've got some truly random data to delete
it happens so that you have at least one row per region to get rid
of... then you need to basically rewrite the whole table?

My answer was such, and I told the attendee that it's not an easy
case to manage in HBase.



Kevin O'Dell
Systems Engineer, Cloudera

Kevin O'Dell
Systems Engineer, Cloudera

Jesse Yates

Todd Lipcon
Software Engineer, Cloudera

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