Some NoSQL Myths

[Tony Bain]

I have been busy travelling recently but thought I would jot down a couple of NoSQL myths that are fresh in my head from my recent discussions. Twitter use Cassandra internally but have not migrated their tweet store, despite their...

I have been busy travelling recently but thought I would jot down a couple of NoSQL myths that are fresh in my head from my recent discussions.

• Twitter use Cassandra internally but have not migrated their tweet store, despite their earlier plans to. *For now tweets are still stored in MySQL.
• Despite the widely accepted view that the use of Cassandra led to Diggs issues a couple of Digg engineers have apparently discounted this.
• Despite the widely accepted view that NoSQL databases all use eventual consistency this is not so. *HBase, for example, offers full consistency.
• Despite the widely accepted view that NoSQL is only about unlimited distributed scalability this is also not so. *Some of the most popular NoSQL platforms have fairly rudimentary (traditional RDBMS like) scalability options. *Such as CouchDB and MongoDB which use sharding + replication to achieve scale.
• Despite being commonly report as “easy to install” or “easy to use” the benefits of a document object model are much more significant. *Why did we spend so much time during the 90’s trying to build ORDBMS? *Because the Object-relational impedance mismatch is major and this translates into significant development overhead. *It is not uncommon to see 30-60% of all code in some applications purely “plumbing” to deal with mapping data to and from the RDBMS. *This is not something necessarily well understood by DBA’s or even some long time database designers, something I will write a follow up post on.

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