Sunday, May 24, 2020

Database Management Systems (DBMS) Question Bank 05

What are the challenges of scaling RDBMS, list the challenges to be faced while scaling the database management system, scaling possibilities for RDBMS


Discuss the challenge of scaling a relational database management system (RDBMS)

In a relational DBMS, the most difficult feature to scale are transactions. If a database grows such that it no longer fits on one server but must instead be spread across multiple servers, then a single transaction may update data on multiple machines. Here, the challenge is about satisfying the ACID properties. In order to provide ACID properties, the transaction must be committed using an expensive two-phase commit protocol that requires multiple rounds of communication between the machines involved.
If a database fits on one machine but must support a high transaction rate, scalability is also a challenge. One solution is to replicate the database such that the requests can be spread across the replicas. For queries that only read data, this approach works very well. In the case of updates, however, the challenge is in keeping the replicas up-to-date. If we need to propagate each update synchronously to all replicas, updates will be slow. If we return to the user without propagating the update to all replicas, some operations can end-up reading stale values and we also risk losing recent updates in case of failures.
Finally, parallel queries that read and process a lot of data nicely scale but they also use a lot of resources.


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