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On 12/07/2010 10:41 AM, Matt Shields wrote:
> I think the NoSQL term "eventually consistant" sums up why it should 
> not be used for all situations.  They say that eventually all data 
> will be committed, but if your bank was running a NoSQL database and 
> you just deposited your money and expected the transaction to show up 
> when you looked at it from your phone and didn't see it there and they 
> told you your account would be "eventually consistant" with what they 
> were telling you, would you be happy?
> How about an environment where you have to make sure that transaction 
> 1 is processed before transaction 2.  From what I've read about NoSQL, 
> they cannot guarantee that.
> Sure, sites like Facebook and Twitter where you have status updates 
> and profiles, this is the perfect place to use NoSQL.

I don't want to come off as a member of the anti-NoSQL  (head spinning 
from negativity :-), but generally speaking, and this is understood to 
be a major generalization, NoSQL advocates don't really seem to get the 
depth that is involved with mature SQL databases.

Data access, searching, indexing, concurrency, consistency, caching, 
ordering, gathering access statistics, etc. are complex problems that 
have been studied for years, and the results and knowledge gained by, 
who knows how many man-lives of research, is embodied in products like 
PostgreSQL, DB2, Oracle, etc. Dismissing them because they are "old" is 
like dismissing algebra because it is an ancient egyptian math construct.

You brought up three very important issues: durability, atomicity and 
consistency. The idea that data is reliably saved, that specific 
transactions are performed individually with data in a known state and 
in the correct order. People have spent years studying how to do this 
well. You can trust a mature sql database to do this quickly and 
efficiently. This very difficult set of problems have been solved for 
you. Don't abandon these amazing systems because of a perception of 
oldness or being out of date. Regardless of whether or not you think you 
"need it," having it will make development easier because your data will 
be predictable.

There is a huge segment of the data storage environment for "NoSQL" type 
systems, but as I said, the preference should be toward using mature SQL 
systems for data and only after you've evaluated the problem as not 
being doable in SQL, then you should employ other systems, not the other 
way around. A SQL database either solves or provides facilities to solve 
an uncountable number of problems that a modern web site will encounter. 
The NoSQL systems merely claim that they scale better, and by scale, I 
mean they abandon "known good practices" in data management in favor of 
potentially more risky ones which may perform better.

> -matt

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