Question

Can you please point to alternative data storage tools and give good reasons to use them instead of good-old relational databases? In my opinion, most applications rarely use the full power of SQL–it would be interesting to see how to build an SQL-free application.

Answer 1

Plain text files in a filesystem

• Very simple to create and edit
• Easy for users to manipulate with simple tools (i.e. text editors, grep etc)
• Efficient storage of binary documents

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XML or JSON files on disk

• As above, but with a bit more ability to validate the structure.

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Spreadsheet / CSV file

• Very easy model for business users to understand

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Subversion (or similar disk based version control system)

• Very good support for versioning of data

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Berkeley DB (Basically, a disk based hashtable)

• Very simple conceptually (just un-typed key/value)
• Quite fast
• No administration overhead
• Supports transactions I believe

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Amazon’s Simple DB

• Much like Berkeley DB I believe, but hosted

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Google’s App Engine Datastore

• Hosted and highly scalable
• Per document key-value storage (i.e. flexible data model)

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CouchDB

• Document focus
• Simple storage of semi-structured / document based data

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Native language collections (stored in memory or serialised on disk)

• Very tight language integration

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Custom (hand-written) storage engine

• Potentially very high performance in required uses cases

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I can’t claim to know anything much about them, but you might also like to look into object database systems.