Андрей Буров

$a=='1';
$b== '2';

$a = '1';
$b = '2';

# strings /usr/lib64/postgresql-9.6/bin/postgres|grep PostgreSQL

This is caused by an incomplete page split at crash recovery before upgrading to PostgreSQL 9.1.
PostgreSQL does not support leap seconds.
postgres (PostgreSQL) 9.6.3
....