I am using Cassandra database and need to define the Primary Key which is a combination of partition key and clustering keys. The cassandra database needs to be queried based on the combination of two fields i.e. a customer number and createdAt (Unix timestamp value), as per the business requirement. These columns cannot be used as Primary key because they cannot uniquely identify a row in the database. So, is it correct to add the uuid column from database as a clustering key to make the primary key unique, so that the Primary key will become a combination of - customerNumber(Partition key), createdAt (ClusteringKey), uuid( clustering key). However the database will never be queried based on the whole primary key. It will always be queried based on the part of the Primary key i.e. Customer Number and createdAt. uuid will never be used to query the database.
Is it necessary to use all the columns defined as the primary key to query a Cassandra database?
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1 Answers
So if I understand correctly, your PRIMARY KEY definition looks like this:
PRIMARY KEY (customerNumber,createdAt,uuid)
It will always be queried based on the part of the Primary key
Yes, querying by part of the PRIMARY KEY definition is fine, in your case. Cassandra tries to restrict queries to a single node, and it achieves this by ensuring that an entire partition is written to a single node (and then replicated). Because of this, you really only need to supply the partition key on your queries (customerNumber), and they should work.
Supplying an additional PRIMARY KEY component however, is helpful. In a high-throughput scenario, the smaller you can keep your result set payloads, the better.
tl;dr;
Querying by customerNumber and createdAt will be just fine.
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