How do I calculate the size of a Cassandra Partition?

Question

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?

Answer 1

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!