CODEWITHSUNDEEP
cassandra
Hadi Moloodi
Hadi Moloodi

Reputation: 639

Cassandra Internal Storage

If I create a table like this in Cassandra

   CREATE TABLE example (  
   key1 text PRIMARY KEY,  
   map1 map<text,text>,  
   list1 list<text>,  
   set1 set<text>
);

and insert some data like this

INSERT INTO example (  
   key1,  
   map1,  
   list1,  
   set1  
) VALUES (  
   'john',  
   {'patricia':'555-4326','doug':'555-1579'},  
   ['doug','scott'],  
   {'patricia','scott'}  
);

and look at the storage using CLI, I will see this

RowKey: john  
=> (column=, value=, timestamp=1374683971220000)  
=> (column=map1:doug, value='555-1579', timestamp=1374683971220000)  
=> (column=map1:patricia, value='555-4326', timestamp=1374683971220000)  
=> (column=list1:26017c10f48711e2801fdf9895e5d0f8, value='doug', timestamp=1374683971220000)  
=> (column=list1:26017c12f48711e2801fdf9895e5d0f8, value='scott', timestamp=1374683971220000)  
=> (column=set1:'patricia', value=, timestamp=1374683971220000)  
=> (column=set1:'scott', value=, timestamp=1374683971220000)

Now my question is this: what is the first row in CLI output? what does it mean? why it does not have any Column nor Value but has a timestamp?

Upvotes: 1

Views: 86

Answers (2)

Schildmeijer
Schildmeijer

Reputation: 20946

The "row marker" was introduced [1] so the row doesn't disappear when you remove (set a column to null) the last column. Aligned with how traditional SQL implementations behaves)

You have also found out how cassandra represents collections under the hood. Remember that

  • Map keys should be unique (solved)
  • List can contain duplicates (solved by appending a uuid)
  • Set should not contain duplicates (solved)

[1] https://issues.apache.org/jira/browse/CASSANDRA-4361

Upvotes: 1

Saifallah KETBI
Saifallah KETBI

Reputation: 313

This because while using cassandra-cli, you get a thrift representation of the rows. First information are for primary key, as your is just a partition key, it's the same as the row key. So you have your value : as rowKey (John in your example) then the timestamp

You will have more readable result set if you usin cqlsh instead. you can find more detail here : https://thelastpickle.com/blog/2013/01/11/primary-keys-in-cql.html

I hope this helps

Upvotes: 0

Related Questions