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javaspring-bootcassandra
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Reputation: 57

Add Column to Cassandra db with out losing data

I am using Cassandra database integrated into a spring boot application.

My Question is around the schema actions. If I need to make structural changes to the DB, say add a column to a table, the database needs to be recreated, however this means all the existing data gets deleted:

schema-action: CREATE_IF_NOT_EXISTS

The only way I have managed to solve this is by using the RECREATE scheme action, but as mentioned earlier, this results in data-loss.

What would be the best approach to handle this? To add structural changes such as a column name with out having to recreate the database and lose all existing data?

Thanks

Upvotes: 0

Views: 655

Answers (1)

Nadav Har'El
Nadav Har'El

Reputation: 13731

Cassandra does allow you to modify the schema of an existing table without recreating it from scratch, using the ALTER TABLE statement via cqlsh. However, as explained in that link, there are some important limitations on the kind of changes you can do. You cannot modify the primary key of the table at all, you can add or delete regular columns, and you can't change the type of a column to a non-compatible one.

The reason for most of these limitations is how Cassandra needs to deal with the old data that already exists in the table. For example, it doesn't make sense to say that a column A that until now contained strings - will now contain integers - how are we supposed to handle all the old values in column A which weren't integers?

As Aaron rightly said in a comment, it is unlikely you'll want to do these schema changes as part of your application. These are usually rare operations which are done manually, or via some management application - not your usual application.

Upvotes: 2

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