How do I calculate the size of a Cassandra Partition?

CREATE TABLE IF NOT EXISTS video (key int, value int, PRIMARY KEY (key, value));

Here Partition Key is key and Clustering Key is value. No regular columns. Assume, there are 1000000 rows in this partition.

What is the size of the partition?

To calculate the partition size, you need the following data points:

• size of the partition key columns
• size of static columns
• size of cells in the partition (clustering + regular columns)
• size of metadata overhead per row

In your case:

• the size the partition key (a single int column) is 4 bytes
• the size of static columns (there are none) is 0 bytes
• the size of the cells (clustering int + 0 regular columns) is 4 + 0 bytes
• the size of the metadata overhead is 8 bytes on average

So for 1M rows:

partition size = 4B + 0B + (4B x 1,000,000 cells) + (8B x 1,000,000,000 rows)
               = 12,000,004 bytes
               = 11.44 MB

Cheers!