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07-20-2023, 01:29 PM
The accepted answer is spot on the basic definition of horizontal vs vertical scaling. But unlike the common belief that horizontal scaling of databases is only possible with Cassandra, MongoDB, etc I would like to add that horizontal scaling is also very much possible with any traditional RDMS; that too without using any third party solutions.
I know of many companies, specially SaaS based companies that do this. This is done using simple application logic. You basically take a set of users and divide them over multiple DB servers. So for example, you would typically have a "meta" database/table that would store clients, DB server/connection strings, etc and a table that stores client/server mapping.
Then simply direct requests from each client to the DB server they are mapped to.
Now some may say this is akin to horizontal partitioning and not "true" horizontal scaling and they will be right in some ways. But the end result is that you have scaled your DB over multiple Db servers.
The only difference between the two approaches to horizontal scaling is that one approach (MongoDB, etc) the scaling is done by the DB software itself. In that sense you are "buying" the scaling. In the other approach (for RDBMS horizontal scaling), the scaling is built by application code/logic.
I know of many companies, specially SaaS based companies that do this. This is done using simple application logic. You basically take a set of users and divide them over multiple DB servers. So for example, you would typically have a "meta" database/table that would store clients, DB server/connection strings, etc and a table that stores client/server mapping.
Then simply direct requests from each client to the DB server they are mapped to.
Now some may say this is akin to horizontal partitioning and not "true" horizontal scaling and they will be right in some ways. But the end result is that you have scaled your DB over multiple Db servers.
The only difference between the two approaches to horizontal scaling is that one approach (MongoDB, etc) the scaling is done by the DB software itself. In that sense you are "buying" the scaling. In the other approach (for RDBMS horizontal scaling), the scaling is built by application code/logic.