public byte[] findStartKeyOfNextRegion(final byte[] key) {
        Requires.requireNonNull(key, "key");
        final StampedLock stampedLock = this.stampedLock;
        long stamp = stampedLock.tryOptimisticRead();
        // get the least key strictly greater than the given key
        byte[] nextStartKey = this.rangeTable.higherKey(key);
        if (!stampedLock.validate(stamp)) {
            stamp = stampedLock.readLock();
            try {
                // get the least key strictly greater than the given key
                nextStartKey = this.rangeTable.higherKey(key);
            } finally {
                stampedLock.unlockRead(stamp);
            }
        }
        return nextStartKey;
    }
Returns the startKey of next region.
jraft-rheakv/rheakv-core/src/main/java/com/alipay/sofa/jraft/rhea/client/RegionRouteTable.java