Jeff Davis <pgsql(at)j-davis(dot)com> writes:
> I can't see any place that "cachedFetchXid" is ever invalidated.
> Shouldn't it be invalidated before transaction ID wraparound?
The assumption is that the value won't sit there (in a particular
session), without ever being replaced, while more than 2G transactions
elapse. Actually you'd need a full 4G transactions to elapse, and then
to wake up just in time to probe the doppelganger of the very same
transaction number, in order to have any risk of a failure.
If that makes you uncomfortable, I've got bad news: there are quite a
few other assumptions of the same ilk about the lifespan of a single
session. One comparable failure case is that starting a transaction
that acquires an XID, and then going to sleep for ~2G transactions,
will cause all kinds of trouble.
regards, tom lane
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