Data manager

At this step, the query manager is executing the query and needs the data from the tables and indexes. It asks the data manager to get the data, but there are 2 problems:

• Relational databases use a transactional model. So, you can’t get any data at any time because someone else might be using/modifying the data at the same time.
• Data retrieval is the slowest operation in a database , therefore the data manager needs to be smart enough to get and keep data in memory buffers.

In this part, we’ll see how relational databases handle these 2 problems. I won’t talk about the way the data manager gets its data because it’s not the most important (and this article is long enough!).