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From Josh Elser <>
Subject Re: [DISCUSS] Would a visibility histogram on a table be harmful?
Date Wed, 12 Oct 2016 16:25:50 GMT
Again, can we please bring this discussion back from discussions of 
implementations to security?

Does the fact that you three were discussing implementations imply that 
you do not think this invalidates one of the core tenets (security 
first) of Accumulo?

Christopher wrote:
> Keith, Russ, myself (and possible others) were discussing this at the
> hackathon after the Accumulo Summit, and I think our consensus were
> basically this:
> We need a generic pluggable mechanism for injecting arbitrary user counters
> into the RFiles. We can then use these counters in custom compaction
> strategies, or other analysis. We can aggregate these counters at the
> tablet, and table levels, and expose them in the API.
> These counters could store information about visibility frequencies, number
> of delete entries, etc.
> The interface might just be a Function<Entry<Key,Value>,Map<String, Long>>.
> In the discussion, there were lots of variations on the theme, though. So,
> the actual implementation could vary. But, having something like this could
> support a large number of use cases beyond just the histogram case.
> On Tue, Oct 11, 2016 at 10:06 PM Josh Elser<>  wrote:
>> Trivially. We could do something more intelligent like also cache it in
>> metadata (updating with compactions). Don't read too much into the
>> implementation at this point; it was just the first idea I had about how we
>> could do it :). I'm more concerned with the idea and its security
>> implications right now.
>> In general, it seems like people are ok with it protected by a new
>> permission role. Do you have more to add, Mike? Was your comment based on
>> your interpretation of how Accumulo works or more a concern about
>> implementing such a feature?
>> On Oct 11, 2016 21:29,<>  wrote:
>>> So, to get the set of visibilities used in a table, we would have to open
>>> all of the rfiles?
>>>> -----Original Message-----
>>>> From: Dylan Hutchison []
>>>> Sent: Tuesday, October 11, 2016 3:43 PM
>>>> To: Accumulo Dev List
>>>> Subject: Re: [DISCUSS] Would a visibility histogram on a table be
>>> harmful?
>>>> Interesting idea.  It begs the question: should we allow any custom
>>> index at
>>>> the RFile level?  If RFile indexes were user-extensible, then a
>>> visibility index
>>>> would be something any developer could write.  That said, we can still
>>>> include such an index as an example, and if we did it could be used by
>>> the
>>>> Accumulo monitor.
>>>> The RFile-level sampling followed this path.  I would support further
>>> work
>>>> similar to it, though I admit I don't know how difficult a job it
>>> entails.
>>>> Bonus points if the index information could be accessed from iterators
>>> the
>>>> same way that sampled data can.
>>>> I can't speak to the appropriateness of visibility histograms on the
>>> monitor
>>>> *by default*, but it would be a strictly useful feature if it could be
>>> enabled via
>>>> a conf option.
>>>> On Tue, Oct 11, 2016 at 12:20 PM, Josh Elser<>
>>> wrote:
>>>>> Today at Accumulo Summit, our own Russ Weeks gave a talk. One topic
>> he
>>>>> mentioned was the lack of insight into the distribution of data
>> marked
>>>>> with certain visibilities in a table. He presented an example similar
>>> to this:
>>>>> Image a hypothetical system backed by Accumulo which stores medical
>>>>> information. There are three labels in the system: PRIVATE,
>>>>> ANONYMIZED, and PUBLIC. PRIVATE data is that which could reasonably
>> be
>>>>> considered to identify the individual. ANONYMIZED data is some
>> altered
>>>>> version of the attribute that retains some portion of the original
>>>>> value, but is missing enough context to not identify the individual
>>>>> (e.g. converting the name "Josh Elser" to "J E"). PUBLIC data is for
>>>>> attributes which are cannot identify the individual.
>>>>> Doctors would be able to read the PRIVATE data, while researchers
>>>>> could only read the ANONYMIZED and PUBLIC data. This leads to a
>>>>> question: how much of each kind of data is in the system? Without
>>>>> knowing how much data is in the system, how can some application
>>>>> developer (who does not have the ability to read all of the PRIVATE
>>>>> data) know that their application is returning an reasonably correct
>>>>> amount of data? (there are many examples of questions which could be
>>>>> answer on this data alone)
>>>>> Concretely, this histogram would look like (50 records with PRIVATE,
>>>>> 50 with ANONYMIZED, and 20 with PUBLIC; 120 records total):
>>>>> ```
>>>>> PRIVATE: 50
>>>>> ANONYMIZED: 50
>>>>> PUBLIC: 20
>>>>> ```
>>>>> Technically, I think this would actually be relatively simple to
>>>>> implement. Inside of each RFile, we could maintain some histogram of
>>>>> the visibilities observed in that file. This would allow us to very
>>>>> easily report how much data in each table has each visibility label.
>>>>> However, would this feature be harmful to one of the core tenants of
>>>>> Accumulo? Or, is acknowledging the existence of data in Accumulo with
>>>>> a certain visibility acceptable? Would a new permission to use such
>> an
>>>>> API to access this information be sufficient to protect the data?
>>>>> - Josh

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