The maze of the elephant

The maze of the elephant

In the previous post we introduced the PostgreSQL’s dependency system.

At first sight the implementation can look like a maze where the succession of relationships are not clear.

This post will try to give a practical example to show how pg_depend can act like an Ariadne’s thread in order to resolve the dependencies.

The scenario presented is very simple but can be used as a starting point for more complex requirements.

The dependency ladder

The dependency ladder

One of the things that distinguish PostgreSQL from other database systems is the way the dependencies between database objects are managed.

PostgreSQL do not allow any invalid object like views or functions. Therefore any action that can invalidate dependent objects results in an error or it’s propagated to the dependent objects.

The mechanism could be confusing at first sight. However the implementation is brilliant and gives great flexibility.

Checkpoints and wals, fantastic beasts (and where to find them)

Checkpoints and wals, fantastic beasts (and where to find them)

Back in the days of when I was an Oracle DBA I had to solve a strange behaviour on an Oracle installation. The system for some reasons stopped accepting the writes occasionally and without an apparent reason. This behaviour appeared odd to anybody except for my team, which addressed the issue immediately. The problem was caused by a not optimal configuration on the Oracle instance. This thought led me to writing this post.