Concepts

E-Maj is built on three core concepts.

Tables Group

A table group represents a set of application tables that share the same lifecycle. This means their content can be restored as a whole if needed. Typically, a table group includes all tables in a database that are updated by one or more sets of programs.

Each table group is identified by a unique name within its database.

Additionally, a table group can also include partitions of partitioned tables and sequences.

Tables (including partitions) and sequences in a table group can belong to different schemas within the database.

At any given time, a table group is in one of two states:

  • LOGGING: Updates applied to the tables in the group are recorded.

  • IDLE: Updates are NOT recorded.

A table group can be either:

  • ROLLBACKABLE (default): Allows reverting recorded changes.

  • AUDIT_ONLY: Reverting recorded changes is NOT possible. This type is useful for tables without an explicitly created PRIMARY KEY or for UNLOGGED tables.

Mark

A mark is a stable reference point in the lifecycle of a table group. It captures the state of all tables and sequences in the group at a specific moment. A mark is explicitly created by a user action

The mark is identified by a unique name within its table group.

Rollback

An E-Maj rollback operation resets all tables and sequences in a group to the state they had when a mark was set.

There are two types of rollback:

  • Unlogged rollback: Changes canceled by the rollback are permanently discarded, with no trace kept in the log tables.

  • Logged rollback: Changes canceled by the rollback are recorded in the log tables, allowing the rollback itself to be reversed later. In other words, a logged rollback can be rolled back.

Note that the E-Maj rollback concept is distinct from PostgreSQL’s transaction rollback mechanism.