When a resource relating to a session is deleted,
notably a target, host, or auth_token, the corresponding sessions are
marked as canceled via a database trigger that calls the cancel_session
function. This function was performing a select as part of the insert
call to ensure that it would not attempt to insert a session_sate of
canceled if it was an invalid state transition. However, since this
function was first introduced, there has been additional constraints
added that would prevent an invalid state transition. In addition,
performing a select as part of an insert increases the chances for
contention with other queries that interact with the session_state
table, especially since a large number of sessions and session_state
rows can be included in a single transaction when things like
auth_tokens or targets get deleted.
Now, the cancel_function will perform the insert, and catch any of the
potential violations, allowing the query to continue without needing to
perform the select, thus reduction the potential for contention.
Timothy Messier
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