ServerLog ERD

The K2ServerLog Database/ServerLog schema contains all current and completed workflow data transactions. It can basically be divided into 2 halves: the Workflow-Definition data and the Workflow-Reporting data.

The Workflow-Definition data contains all the process definitions. The reason that this data is duplicated here (when one would expect that this data would only appear within the Transaction database) is that reporting components (such as K2 View Flow) make use of this definition data in order to render a view of the process definition, and thereupon overlay the reporting data over it.
The following pdf document contains ERD diagram for Workflow-Definition tables: Workflow Definition ERD

The Workflow-Reporting (also called the Instance data) contains all the data for the running instances of processes and their components. This potentially includes detail all the way down to audit data for the changing of process and activity data. The level of data logging is set in the K2 Service Manager, and can be set per process. By default, all details for each process are logged.
The following pdf document contains ERD diagram for the Workflow-Reporting tables: Workflow Reporting ERD

The only component that logs any data into the Log database is the K2LogServer. All other components merely read data from within this database.