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From Frank LoVecchio <fr...@isidorey.com>
Subject Re: Do supercolumns have a purpose?
Date Thu, 10 Feb 2011 18:16:38 GMT
I've found super column families quite useful when using
RandomOrderedPartioner on a low-maintenance cluster (as opposed to
Byte/Ordered), e.g. returning ordered data from a TimeUUID comparator type;
try doing that with one regular column family and secondary indexes (you
could obviously sort on the client side, but that is tedious and not logical
for older data).

On Thu, Feb 10, 2011 at 12:32 AM, David Boxenhorn <david@lookin2.com> wrote:

> Mike, my problem is that I have an database and codebase that already uses
> supercolumns. If I had to do it over, it wouldn't use them, for the reasons
> you point out. In fact, I have a feeling that over time supercolumns will
> become deprecated de facto, if not de jure. That's why I would like to see
> them represented internally as regular columns, with an upgrade path for
> backward compatibility.
>
> I would love to do it myself! (I haven't looked at the code base, but I
> don't understand why it should be so hard.) But my employer has other
> ideas...
>
>
> On Wed, Feb 9, 2011 at 8:14 PM, Mike Malone <mike@simplegeo.com> wrote:
>
>> On Tue, Feb 8, 2011 at 2:03 AM, David Boxenhorn <david@lookin2.com>wrote:
>>
>>> Shaun, I agree with you, but marking them as deprecated is not good
>>> enough for me. I can't easily stop using supercolumns. I need an upgrade
>>> path.
>>>
>>
>> David,
>>
>> Cassandra is open source and community developed. The right thing to do is
>> what's best for the community, which sometimes conflicts with what's best
>> for individual users. Such strife should be minimized, it will never be
>> eliminated. Luckily, because this is an open source, liberal licensed
>> project, if you feel strongly about something you should feel free to add
>> whatever features you want yourself. I'm sure other people in your situation
>> will thank you for it.
>>
>> At a minimum I think it would behoove you to re-read some of the comments
>> here re: why super columns aren't really needed and take another look at
>> your data model and code. I would actually be quite surprised to find a use
>> of super columns that could not be trivially converted to normal columns. In
>> fact, it should be possible to do at the framework/client library layer -
>> you probably wouldn't even need to change any application code.
>>
>> Mike
>>
>> On Tue, Feb 8, 2011 at 3:53 AM, Shaun Cutts <shaun@cuttshome.net> wrote:
>>>
>>>>
>>>> I'm a newbie here, but, with apologies for my presumptuousness, I think
>>>> you should deprecate SuperColumns. They are already distracting you, and
as
>>>> the years go by the cost of supporting them as you add more and more
>>>> functionality is only likely to get worse. It would be better to concentrate
>>>> on making the "core" column families better (and I'm sure we can all think
>>>> of lots of things we'd like).
>>>>
>>>> Just dropping SuperColumns would be bad for your reputation -- and for
>>>> users like David who are currently using them. But if you mark them clearly
>>>> as deprecated and explain why and what to do instead (perhaps putting a bit
>>>> of effort into migration tools... or even a "virtual" layer supporting
>>>> arbitrary hierarchical data), then you can drop them in a few years (when
>>>> you get to 1.0, say), without people feeling betrayed.
>>>>
>>>> -- Shaun
>>>>
>>>> On Feb 6, 2011, at 3:48 AM, David Boxenhorn wrote:
>>>>
>>>> "My main point was to say that it's think it is better to create tickets
>>>> for what you want, rather than for something else completely different that
>>>> would, as a by-product, give you what you want."
>>>>
>>>> Then let me say what I want: I want supercolumn families to have any
>>>> feature that regular column families have.
>>>>
>>>> My data model is full of supercolumns. I used them, even though I knew
>>>> it didn't *have to*, "because they were there", which implied to me that
I
>>>> was supposed to use them for some good reason. Now I suspect that they will
>>>> gradually become less and less functional, as features are added to regular
>>>> column families and not supported for supercolumn families.
>>>>
>>>>
>>>> On Fri, Feb 4, 2011 at 10:58 AM, Sylvain Lebresne <sylvain@datastax.com
>>>> > wrote:
>>>>
>>>>> On Fri, Feb 4, 2011 at 12:35 AM, Mike Malone <mike@simplegeo.com>wrote:
>>>>>
>>>>>> On Thu, Feb 3, 2011 at 6:44 AM, Sylvain Lebresne <
>>>>>> sylvain@datastax.com> wrote:
>>>>>>
>>>>>>> On Thu, Feb 3, 2011 at 3:00 PM, David Boxenhorn <david@lookin2.com>wrote:
>>>>>>>
>>>>>>>> The advantage would be to enable secondary indexes on supercolumn
>>>>>>>> families.
>>>>>>>>
>>>>>>>
>>>>>>> Then I suggest opening a ticket for adding secondary indexes
to
>>>>>>> supercolumn families and voting on it. This will be 1 or 2 order
of
>>>>>>> magnitude less work than getting rid of super column internally,
and
>>>>>>> probably a much better solution anyway.
>>>>>>>
>>>>>>
>>>>>> I realize that this is largely subjective, and on such matters code
>>>>>> speaks louder than words, but I don't think I agree with you on the
issue of
>>>>>> which alternative is less work, or even which is a better solution.
>>>>>>
>>>>>
>>>>> You are right, I put probably too much emphase in that sentence. My
>>>>> main point was to say that it's think it is better to create tickets
for
>>>>> what you want, rather than for something else completely different that
>>>>> would, as a by-product, give you what you want.
>>>>> Then I suspect that *if* the only goal is to get secondary indexes on
>>>>> super columns, then there is a good chance this would be less work than
>>>>> getting rid of super columns. But to be fair, secondary indexes on super
>>>>> columns may not make too much sense without #598, which itself would
require
>>>>> quite some work, so clearly I spoke a bit quickly.
>>>>>
>>>>>
>>>>>> If the goal is to have a hierarchical model, limiting the depth to
two
>>>>>> seems arbitrary. Why not go all the way and allow an arbitrarily
deep
>>>>>> hierarchy?
>>>>>>
>>>>>> If a more sophisticated hierarchical model is deemed unnecessary,
or
>>>>>> impractical, allowing a depth of two seems inconsistent and
>>>>>> unnecessary. It's pretty trivial to overlay a hierarchical model
on top of
>>>>>> the map-of-sorted-maps model that Cassandra implements. Ed Anuff
has
>>>>>> implemented a custom comparator that does the job [1]. Google's Megastore
>>>>>> has a similar architecture and goes even further [2].
>>>>>>
>>>>>> It seems to me that super columns are a historical artifact from
>>>>>> Cassandra's early life as Facebook's inbox storage system. They needed
>>>>>> posting lists of messages, sharded by user. So that's what they built.
In my
>>>>>> dealings with the Cassandra code, super columns end up making a mess
all
>>>>>> over the place when algorithms need to be special cased and branch
based on
>>>>>> the column/supercolumn distinction.
>>>>>>
>>>>>> I won't even mention what it does to the thrift interface.
>>>>>>
>>>>>
>>>>> Actually, I agree with you, more than you know. If I were to start
>>>>> coding Cassandra now, I wouldn't include super columns (and I would probably
>>>>> not go for a depth unlimited hierarchical model either). But it's there
and
>>>>> I'm not sure getting rid of them fully (meaning, including in thrift)
is an
>>>>> option (it would be a big compatibility breakage). And (even though I
>>>>> certainly though about this more than once :)) I'm slightly
>>>>> less enthusiastic about keeping them in thrift but encoding them in regular
>>>>> column family internally: it would still be a lot of work but we would
still
>>>>> probably end up with nasty tricks to stick to the thrift api.
>>>>>
>>>>> --
>>>>> Sylvain
>>>>>
>>>>>
>>>>>> Mike
>>>>>>
>>>>>> [1] http://www.anuff.com/2010/07/secondary-indexes-in-cassandra.html
>>>>>> [2] http://www.cidrdb.org/cidr2011/Papers/CIDR11_Paper32.pdf
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>
>>
>


-- 
Frank LoVecchio
Senior Software Engineer | Isidorey, LLC
Google Voice +1.720.295.9179
isidorey.com | facebook.com/franklovecchio | franklovecchio.com |
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