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HBase >> mail # user >> When to expand vertically vs. horizontally in Hbase


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Re: When to expand vertically vs. horizontally in Hbase
Sure. Maybe it's useful to talk about the functional aspect of relationships in models. In an RDBMS, explicit relationship play a couple roles:

- foreign key constraints: don't allow a tuple in relation A to point to a row in relation B that doesn't exist
- join optimization - knowledge of how two relations are logically connected can help perform joins in a more optimal way

HBase, of course, provides neither of these features out of the box, so there is no difference between an implied (weakly coupled, to use your term) relationship and something stronger.

Where it gets interesting is in the kind of denormalization you're talking about, where information that properly belongs to one entity is copied into another one for efficiency's sake, or to get some kind of atomicity protection. Your scenario below is doing this (duplicating customer info in the order records).

To be fair, relational DBs also force this kind of behavior sometimes, again for efficiency reasons (we've all done it). HBase just starts there. :)

Ian

On Jul 5, 2013, at 4:22 PM, "Michael Segel" <[EMAIL PROTECTED]> wrote:

> An entity is an entity.
> When you couple them you are saying that there's a relationship to them in the model.
>
> What I am saying is that you can have an HBase model which is not a single table, however when you look at your use case, you are querying data from a single table at a time.
>
> Going back to the order entry system. You may have a customer table which maintains all of the information about your customer yet you will also duplicate portions of the data in to the order system.  You still have other entities such as your orders, pick slips, shipping and invoices. There won't be a hard or strong relationship between the customer table and the order table.
>
> When you go to your ERD tool, you wouldn't show a strong coupling of the data.
>
> Does that make sense?
>
> On Jul 5, 2013, at 1:56 PM, Ian Varley <[EMAIL PROTECTED]> wrote:
>
>> Mike, what do you mean by "you can have entities, except that they are not coupled"? You mean, they have no relationship to each other? Or the relationship is defined elsewhere (e.g. application code)? The concept of "coupling" seems a little overloaded and not as concise here as "relationship". Two tuples in a database can have a wide number of relationships to each other; the kinds of relationships that are actively supported differs between a traditional RDBMS and HBase, and proper HBase design requires understand these limitations precisely.
>>
>> I'm not trying to be an ER<http://en.wikipedia.org/wiki/Entity%E2%80%93relationship_model> apologist, there are a lot of ways in which it sucks. :) But if we want to evolve, we can't just pretend there's no history here to build on.
>>
>> Ian
>>
>> On Jul 5, 2013, at 1:41 PM, Michael Segel wrote:
>>
>> LOL...
>>
>> Ian wrote:
>> "But, something just occurred to me: just because your physical implementation (HBase) doesn't support normalized entities and relationships doesn't mean your *problem* doesn't have entities and relationships. :) An Author is one entity, a Title is another, and a Genre is a third. Understanding how they interact is a prerequisite for translating into a physical model that works well in HBase. (ERD modeling is not categorically the only way to understand that, but I've yet to hear a credible alternative that doesn't boil down to either ERD or "do it in your head").
>> "
>>
>> You can have entities, except that they are not coupled.
>>
>> If you have a common key, then you may have a use for column families, it just depends on your data and how you access your data.
>>
>> Its not rocket science, but its a non-trivial matter. Not doing it right may mean that you are not going to get the most out of your system.
>>
>>
>> On Jul 5, 2013, at 1:26 PM, Ian Varley <[EMAIL PROTECTED]<mailto:[EMAIL PROTECTED]>> wrote:
>>
>> But, something just occurred to me: just because your physical implementation (HBase) doesn't support normalized entities and relationships doesn't mean your *problem* doesn't have entities and relationships. :) An Author is one entity, a Title is another, and a Genre is a third. Understanding how they interact is a prerequisite for translating into a physical model that works well in HBase. (ERD modeling is not categorically the only way to understand that, but I've yet to hear a credible alternative that doesn't boil down to either ERD or "do it in your head").
NEW: Monitor These Apps!
elasticsearch, apache solr, apache hbase, hadoop, redis, casssandra, amazon cloudwatch, mysql, memcached, apache kafka, apache zookeeper, apache storm, ubuntu, centOS, red hat, debian, puppet labs, java, senseiDB