Here is the back trace from the core dump attached.
(gdb) bt
#0 0x00007f4a71424495 in raise () from /lib64/libc.so.6
#1 0x00007f4a71425c75 in abort () from /lib64/libc.so.6
#2 0x00000000009dc18a in ExceptionalCondition (conditionName=0xa905d0 "!(TransactionIdPrecedesOrEquals(oldestXact, ShmemVariableCache->oldestXid))",
errorType=0xa9044f "FailedAssertion", fileName=0xa90448 "clog.c", lineNumber=683) at assert.c:54
#3 0x0000000000524215 in TruncateCLOG (oldestXact=150036635, oldestxid_datoid=13164) at clog.c:682
#4 0x00000000006a6be8 in vac_truncate_clog (frozenXID=150036635, minMulti=1, lastSaneFrozenXid=200562449, lastSaneMinMulti=1) at vacuum.c:1197
#5 0x00000000006a6948 in vac_update_datfrozenxid () at vacuum.c:1063
#6 0x00000000007ce0a2 in do_autovacuum () at autovacuum.c:2625
#7 0x00000000007cc987 in AutoVacWorkerMain (argc=0, argv=0x0) at autovacuum.c:1715
#8 0x00000000007cc562 in StartAutoVacWorker () at autovacuum.c:1512
#9 0x00000000007e2acd in StartAutovacuumWorker () at postmaster.c:5414
#10 0x00000000007e257e in sigusr1_handler (postgres_signal_arg=10) at postmaster.c:5111
#11 <signal handler called>
#12 0x00007f4a714d3603 in __select_nocancel () from /lib64/libc.so.6
#13 0x00000000007dde88 in ServerLoop () at postmaster.c:1717
#14 0x00000000007dd67d in PostmasterMain (argc=3, argv=0x2eb8b00) at postmaster.c:1361
#15 0x000000000071a218 in main (argc=3, argv=0x2eb8b00) at main.c:228
(gdb) print ShmemVariableCache->oldestXid
$3 = 548