Is DynamoDB a wide-column store?

Question

Sources indicate that DynamoDB is a key/value store, document store, and/or wide-column store:

At the core, DynamoDB is a key/value store.

If the value stored is a document, DynamoDB provides some support for working with the underlying document. Even Amazon agrees. So far, so good.

However, I've seen some claims that DynamoDB is actually a wide-column store (1, 2, 3, etc.). This seems odd to me, since as I understand it, a wide-column store would technically require a different data storage model.

Is it appropriate to consider DynamoDB to be a wide-column store?

Answer 1

How does Wikipedia define a wide-column store?

https://en.wikipedia.org/wiki/Wide-column_store opens with:

A wide-column store (or extensible record store) is a type of NoSQL database. It uses tables, rows, and columns, but unlike a relational database, the names and format of the columns can vary from row to row in the same table. A wide-column store can be interpreted as a two-dimensional key–value store.

DynamoDB has tables, rows (called items), and columns (called attributes). The names and format can vary from row to row (except for the primary key).

I think most wide-column stores define their table's schema centrally while DynamoDB lets each item define its own schema.

A simple key-value store would only let you look up by a key value. DynamoDB gives you a lot more choices.

At the end of the day this nomenclature is just our collective attempt to group things into similar buckets. There's naturally going to be some fuzzy edges.

Answer 2

In How do you call the data model of DynamoDB and Cassandra? I asked a similar question. I noted that both Cassandra and DynamoDB, which have a very similar data model, are sometimes called "wide-column store" because of its sort key feature:

In DynamoDB (and in Cassandra), items are stored inside a partition contiguously, sorted by the so-called "sort key". To locate an item, you need to specify its partition key, and inside that partition, specify its sort key. This is exactly the two-dimensional key-value store described in Wikipedia's definition of wide-column store https://en.wikipedia.org/wiki/Wide-column_store.

The historic evolution of a wide-column store into a DynamoDB-like one is easier to understand in the context of Cassandra, whose data model is more-or-less the same as DynamoDB's: Cassandra started its life as a real "wide column store": Each row (called "partition") had an unlimited number of unrelated columns. Later, CQL was introduced which added the concept of a "clustering key" (this is Cassandra's equivalent of DynamoDB's sort key), and now each partition was no longer a very long list of unrelated columns - instead it became a very long (and sorted) list of separate items. I explained this evolution in my answer https://stackoverflow.com/a/47127723/8891224 comparing Cassandra's data model to Google Bigtable, which was the quintessential wide-column store.

Answer 3

To add up to the the great answer by Nadav, be careful with considering DynamoDB as wide column datastore...

Of course you can use wide-column-datastore patterns with DynamoDB with key range queries for instance (but the sortKey must be built smartly, nothing can prevent you from errors) but there is a hard limit to it, and it is the item size of a row that is limited to 400KB. This is great for most cases, but very narrow if you want to put, say hundreds of columns of data. And that is generally what you want to do with wide column datastores. Going around the limit is hell to put simply, you will add other tables and joins to compensate.

If you are really interested with using a columnar datastore on AWS, I personally would use AWS Keyspaces for that, it doesn't have the limits of DynamoDB. It will require you to design a database schema, but if you have so many columns, I see it as a plus. CQL is also better than DDB query API.