Another aspect of maintaining a highly available database is to know all important information about the contents of the database itself. In this case, we aim to focus on tables and indexes that receive the most activity. If any problems that might require maintenance or a restart arise, the most active portions are the likely origin.

What is activity? Inserts, updates, deletes, and selects are a good start. PostgreSQL collects statistics on all of this information, making it easy to collect and track. It also tracks how often indexes or tables are scanned and how many rows were affected by each. In addition, we can find out how much disk space any object consumes, and given the help of a couple contributed tools, we can also find out how much of this space is currently reusable.

Data like this tells us which tables and indexes are the most active, which objects have the highest row turnover, and which objects require a high disk I/O. Armed with these statistics...