transactions will not assume that MyProc transaction was committed
before snapshot calculations. With old MyProc->xid assignment
(in xact.c:StartTransaction()) there was ability to see the same
row twice (I used gdb for this)!...
2. Assignments of InvalidTransactionId to MyProc->xid and MyProc->xmin
are moved from xact.c:CommitTransaction() to
xact.c:RecordTransactionCommit() - this invalidation must be done
before releasing transaction locks or bad (too high) XmaxRecent value
might be used by vacuum ("ERROR: Child itemid marked as unused"
reported by "Hiroshi Inoue" <Inoue@tpf.co.jp>; once again, gdb
allowed me reproduce this error).
9680a71205