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defe936ef8
vac_truncate_clog() uses its own transaction ID as the comparison point in a sanity check that no database's datfrozenxid has already wrapped around "into the future". That was probably fine when written, but in a lazy vacuum we won't have assigned an XID, so calling GetCurrentTransactionId() causes an XID to be assigned when otherwise one would not be. Most of the time that's not a big problem ... but if we are hard up against the wraparound limit, consuming XIDs during antiwraparound vacuums is a very bad thing. Instead, use ReadNewTransactionId(), which not only avoids this problem but is in itself a better comparison point to test whether wraparound has already occurred. Report and patch by Alexander Korotkov. Back-patch to all versions. Report: <CAPpHfdspOkmiQsxh-UZw2chM6dRMwXAJGEmmbmqYR=yvM7-s6A@mail.gmail.com>