PostgreSQL RDBMS is a complex piece of software that comprises many
subsystems, and its overall performance depends on these subsystems.
For an optimal performance, Postgres collects various statistics and
information from these subsystems. This helps Postgres to estimate its
effectiveness and act to improve the performance. However, there is a
lot of this information and statistics, and it is too complex to be
interpreted easily. Statistics processing and correct interpretation
is not an easy task itself, but, to make the matter worse, there are
plenty of available tools that may confuse even an experienced DBA.