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From Mike Malone <m...@simplegeo.com>
Subject Re: Do supercolumns have a purpose?
Date Wed, 09 Feb 2011 18:14:22 GMT
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
>>>>
>>>
>>>
>>
>>
>

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