If they are defined, they can override table-level settings.
static void assertSessionIsNotExpired(zkutil::ZooKeeperPtr & zookeeper)
{
    if (!zookeeper)
        throw Exception("No ZooKeeper session.", ErrorCodes::NO_ZOOKEEPER);
    if (zookeeper->expired())
        throw Exception("ZooKeeper session has been expired.", ErrorCodes::NO_ZOOKEEPER);
}
void ReplicatedMergeTreeSink::checkQuorumPrecondition(zkutil::ZooKeeperPtr & zookeeper)