Re: Is txid_status() actually safe? / What is 011_crash_recovery.pl testing?

The txid_status() function was originally intended to be paired with a way to report topxid assignment to the client automatically, NOTIFY or GUC_REPORT-style. But that would not make this usage safe either, unless we delayed the report until WAL was flushed past the LSN of the xid assignment *or* some other txn with a greater xid committed.

This could be made safe with a variant of txid_current() that forced the xid assignment to be logged immediately if it was not already, and did not return until WAL flushed past the point of the assignment. If the client did most of the txn's work before requesting a guaranteed-durable xid, it would in practice not land up having to wait for a flush. But we'd have to keep track of when we assigned the xid in every single topxact in order to be able to promise we'd flushed it without having to immediately force a flush. That's pointless overhead all the rest of the time, just in case someone wants to get an xid for later use with txid_status().