Just like your house gets dirty and requires cleaning from time to time, your PostgreSQL database may accumulate “dust” too. Unwanted pieces of data make the DB grow bigger and bigger. However, there is a mechanism to get rid of junk data and the DB can do it automatically for you.How Does a Database Get “Dirty”?Let’s talk a little bit about concurrency in databases. Generally, when multiple users (or more concretely – database transactions) read or modify the data stored in a database at the same time, they may conflict with each other. One user wants to read the row while another one may want to modify it. They do these operations within different transactions so they should be able to do their jobs without worrying about someone else doing something with the same data. It’s the DBMS’s job to handle it. So let’s look at this problem from a DBMS’s perspective. There are a few possible strategies to do this.