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Comment by zaphar | Hacker News Reader

If it stores data it's a database. Filesystems are databases, MongoDB is a database. LevelDB is a database. Postgres and MySQL are databases. Kafka is a database. They are all very different in features and functionality though.

What the authors mean is that kafka is not a traditional database and doesn't solve the same problems that traditional databases solve. Which is a useful distinction to make but is not the distinction they make.

The reality is that database is now a very general term and for many usecases you can choose to special purpose databases for what you need.

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I think I'd differentiate between a database and a data store.

I'd argue that a filesystem is a data store, rather than a database.

Some say that Microsoft Excel is the world's most popular database engine.

Honestly, I'd agree with that, too, at least in a colloquial sense.

The most popular database where the number of concurrent users = 1

Depends on how many people are looking over your shoulder.

Excel allows you to perform queries for almost arbitrary data on a spreadsheet. I wouldn't doubt for a minute that with sufficient time and motivation you could write a full sql engine with excel functions.

Excel has had a robust built-in columnar database along with decent query semantics and data modeling for awhile now (Power Query/Power Pivot).

I’d say initially file systems were data stores but once they developed hierarchies they became more akin to a database. I’m not sure there’s a huge difference but it seems a database is a collection of data stores (though there or probably a more technical and correct definition.)

What is your distinction? Is mongodb a database? What about leveldb?

Whether we want it to be so or not the term database is much more encompassing thank it used to be. You can try to fight that change if you want to but it means you'll be speaking a different language that most of the rest of us as a result.

You're using the term "traditional database" two levels up. Whatever your definition of that is, it's their definition of "database".

Your initial post says "I have a different definition of 'database'", which is different than anyone else's, as you acknowledge when you refer to that common definition as a 'traditional database'.

Then, you fault them for making an argument that is invalid for your non-standard definition of a database!

You would like Kafka, the author.

No my post said that the term database has evolved beyond their definition. If you want to fight that trend then you will be swimming against the current.

Honestly, where I'd draw the distinction between a database and a datastore is the ability to do multi-statement transactions. So, a filesystem? A datastore. Some support fsync on a single file, but multi-file sync isn't usually supported.

MongoDB and LevelDB both support transactions, so I'd err on calling them databases myself.

I would draw the line at semantic indexing. If the data is only accessible through immediate metadata (filename, sequence number, datetime, etc) then it's just a data_store_. If the engine also maintains indexes derived from the data being stored, then it's a data_base_. In that regard, Kakfa would not be a database since it has no knowledge of what it is storing.

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