This replaces the start_time, end_time, and previous_end_time columns on
the session_state table with a time range column that records when the
state was active. This allowed for dropping several constraints on the
session_state table that were used to ensure that states for a session
did not overlap. Instead this can be ensured with a single exclusion
constraint. By reducing the number of constraints, it improves the
performance for a number of queries involved with session state. Most
notably when resolving delete cascades of resources related to sessions,
such as targets, where as part of the delete transaction large numbers
of sessions get canceled. Similarly, when sessions get deleted, and the
corresponding session_state rows are deleted, these constraints all must
be checked during the transaction.
The domain layer continues to expose StartTime and EndTime fields on
session.State. However it drops PreviousEndTime, which was never used by
anything calling the domain layer.
See:
https://www.postgresql.org/docs/current/ddl-constraints.html#DDL-CONSTRAINTS-EXCLUSIONhttps://www.postgresql.org/docs/current/rangetypes.html
Timothy Messier
Todd
