SSI error messages

Some of these new error messages from the SSI code are a mouthful:

not enough elements in RWConflictPool to record a rw-conflict
not enough elements in RWConflictPool to record a potential rw-conflict

These are basically "out of shared memory" conditions that could be
moved to a DETAIL message.

Canceled on identification as a pivot, during conflict out checking.
Canceled on conflict out to old pivot %u.
Canceled on identification as a pivot, with conflict out to old committed transaction %u.
Canceled on conflict out to old pivot.
Canceled on identification as a pivot, during conflict in checking.
Canceled on identification as a pivot, during write.
Canceled on conflict out to pivot %u, during read.
Canceled on identification as a pivot, during commit attempt.
Canceled on commit attempt with conflict in from prepared pivot.

These are DETAIL messages, with the rest of the report saying

ERROR: could not serialize access due to read/write dependencies among transactions
HINT: The transaction might succeed if retried.

AFAICT, the documentation doesn't mention anything about this "pivot"
that keeps coming up. Is it useful that have the user face this
information? Is there anything a user can derive from seeing one of
these messages versus another, and in addition to the error and hint,
that would help them address the situation?