[rt-users] RT 4.4.1 and transaction isolation level on Postgres

[Alex Vandiver]

On Mon, 2 Jan 2017 17:12:29 +0100
Václav Ovsík <vaclav.ovsik at i.cz> wrote:
> Can anybody confirm on different system?

Thanks for the detailed replication instructions.  I can replicate, and
have tracked down a minimal replication case.  I'll drop my findings
and suggestion on your ticket.

The short form is that this is due to 4.4's new PreviewScrips
functionality, which simulates (then rolls back) all of the changes,
which is racing with the actual change.  The bad news is that it's the
real change, not the dry run, which gets killed in the deadlock
detector, meaning that the owner does go unchanged.  At least this is
bubbled up to the user in the ticket display page, but this is still
quite unfortunate.

Amusingly, there are some strong parallels to the canonical Therac-25
case[1] -- the race here requires that one trigger a PreviewScrips very
quickly before submitting, which is rare except with users quite
accustomed to the UI.  In the Therac-25 case, only skilled users
could navigate to the bottom of the form within 8 seconds and thus
deliver lethal doses of radiation to their patients.

...RT is designed to be robust, but there's a reason it doesn't rate
itself as meant to be used for safety- or life-critical applications.

 - Alex


[1] https://en.wikipedia.org/wiki/Therac-25