I can iterate over JSON data stored in mongo and present it as a table with rows and columns. It does not make mongo a rowstore. 

On Fri, Sep 30, 2016 at 9:16 PM, Edward Capriolo <edlinuxguru@gmail.com> wrote:
The problem with calling it a row store:


In the context of a relational database, a row—also called a record or tuple—represents a single, implicitly structured data item in a table. In simple terms, a database table can be thought of as consisting of rows andcolumns or fields.[1] Each row in a table represents a set of related data, and every row in the table has the same structure.

When you have static columns and rows with maps, and lists, it is hard to argue that every row has the same structure. Physically at the storage layer they do not have the same structure and logically when accessing the data they barely have the same structure, as the static column is just appearing inside each row it is actually not contained in.

On Fri, Sep 30, 2016 at 4:47 PM, Jonathan Haddad <jon@jonhaddad.com> wrote:
+1000 to what Benedict says. I usually call it a "partitioned row store" which usually needs some extra explanation but is more accurate than "column family" or whatever other thrift era terminology people still use.
On Fri, Sep 30, 2016 at 1:53 PM DuyHai Doan <doanduyhai@gmail.com> wrote:
I used to present Cassandra as a NoSQL datastore with "distributed" table. This definition is closer to CQL and has some academic background (distributed hash table).

On Fri, Sep 30, 2016 at 7:43 PM, Benedict Elliott Smith <benedict@apache.org> wrote:
Cassandra is not a "wide column store" anymore.  It has a schema.  Only thrift users no longer think they have a schema (though they do), and thrift is being deprecated.

I really wish everyone would kill the term "wide column store" with fire.  It seems to have never meant anything beyond "schema-less, row-oriented", and a "column store" means literally the opposite of this.

Not only that, but people don't even seem to realise the term "column store" existed long before "wide column store" and the latter is often abbreviated to the former, as here: http://www.planetcassandra.org/what-is-nosql/ 

Since it no longer applies, let's all agree as a community to forget this awful nomenclature ever existed.

On 30 September 2016 at 18:09, Joaquin Casares <joaquin@thelastpickle.com> wrote:
Hi Mehdi,

I can help clarify a few things.

As Carlos said, Cassandra is a Wide Column Store. Theoretically a row can have 2 billion columns, but in practice it shouldn't have more than 100 million columns.

Cassandra partitions data to certain nodes based on the partition key(s), but does provide the option of setting zero or more clustering keys. Together, the partition key(s) and clustering key(s) form the primary key.

When writing to Cassandra, you will need to provide the full primary key, however, when reading from Cassandra, you only need to provide the full partition key.

When you only provide the partition key for a read operation, you're able to return all columns that exist on that partition with low latency. These columns are displayed as "CQL rows" to make it easier to reason about.

Consider the schema:

  bar uuid,
  boz uuid,
  baz timeuuid,
  data1 text,
  data2 text,
  PRIMARY KEY ((bar, boz), baz)

When you write to Cassandra you will need to send bar, boz, and baz and optionally data*, if it's relevant for that CQL row. If you chose not to define a data* field for a particular CQL row, then nothing is stored nor allocated on disk. But I wouldn't consider that caveat to be "schema-less".

However, all writes to the same bar/boz will end up on the same Cassandra replica set (a configurable number of nodes) and be stored on the same place(s) on disk within the SSTable(s). And on disk, each field that's not a partition key is stored as a column, including clustering keys (this is optimized in Cassandra 3+, but now we're getting deep into internals).

In this way you can get fast responses for all activity for bar/boz either over time, or for a specific time, with roughly the same number of disk seeks, with varying lengths on the disk scans.

Hope that helps!

Joaquin Casares
Austin, TX

Apache Cassandra Consulting

On Fri, Sep 30, 2016 at 11:40 AM, Carlos Alonso <info@mrcalonso.com> wrote:
Cassandra is a Wide Column Store http://db-engines.com/en/system/Cassandra

Carlos Alonso | Software Engineer | @calonso

On 30 September 2016 at 18:24, Mehdi Bada <mehdi.bada@dbi-services.com> wrote:
Hi all,

I have a theoritical question:
- Is Apache Cassandra really a column store?
Column store mean storing the data as column rather than as a rows.

In fact C* store the data as row, and data is partionned with row key.

Finally, for me, Cassandra is a row oriented schema less DBMS.... Is it true for you also???

Many thanks in advance for your reply

Best Regards
Mehdi Bada

Mehdi Bada | Consultant
Phone: +41 32 422 96 00 | Mobile: +41 79 928 75 48 | Fax: +41 32 422 96 15
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