Let me confirm I got you right. So, by exception you mean the authentication/authorization/validation functions would return false in case of DB failure?
From what I read about WAL (you have been referring to this: http://www.postgresql.org/docs/current/static/wal-internals.html pg_xlog, right?) it allows us to know what happened, but does it warranty known secure state? I mean, I do not think it would help with this:
"In general, security mechanisms should be designed so that a failure will follow the same execution path as disallowing the operation. For example, application security methods, such as isAuthorized(), isAuthenticated(), and validate(), should all return false if there is an exception during processing. If security controls can throw exceptions, they must be very clear about exactly what that condition means. "
You are correct, that isn't the pg_xlog but yes, PostgreSQL will throw an exception in those types of cases.
Sincerely,
JD
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