Custom Transactional Apache Ignite queue

MyIgniteQueue.java

import org.apache.ignite.Ignite;
import org.apache.ignite.IgniteCache;
import org.apache.ignite.configuration.CacheConfiguration;
import org.apache.ignite.lang.IgniteBiTuple;
import org.apache.ignite.transactions.Transaction;
import org.apache.ignite.transactions.TransactionConcurrency;
import org.apache.ignite.transactions.TransactionIsolation;

import static org.apache.ignite.cache.CacheAtomicityMode.TRANSACTIONAL;

public class MyQueue {
    private static final String HEADER_KEY = "QUEUE_HEADER";

    private final IgniteCache<Object, Object> cache;

    private final Ignite ignite;

    public MyQueue(Ignite ignite, String name) {
        this.ignite = ignite;

        CacheConfiguration<Object, Object> cacheCfg = new CacheConfiguration<>("my-queue")
                .setAtomicityMode(TRANSACTIONAL);

        cache = ignite.createCache(cacheCfg);

        cache.put(HEADER_KEY, new IgniteBiTuple<>(0L, 0L));
    }

    public boolean offer(Object item) {
        try (Transaction tx = txStart()) {
            IgniteBiTuple<Long, Long> header = (IgniteBiTuple<Long, Long>) cache.get(HEADER_KEY);
            long tail = header.get2();

            cache.put(tail, item);
            cache.put(HEADER_KEY, new IgniteBiTuple<>(header.get1(), tail + 1));

            tx.commit();

            return true;
        }
    }

    public Object poll() {
        try (Transaction tx = txStart()) {
            IgniteBiTuple<Long, Long> header = (IgniteBiTuple<Long, Long>) cache.get(HEADER_KEY);

            long head = header.get1();
            Long tail = header.get2();

            if (head >= tail) {
                return null;
            }

            Object item = cache.getAndRemove(head);
            cache.put(HEADER_KEY, new IgniteBiTuple<>(head + 1, tail));

            tx.commit();

            return item;
        }
    }

    private Transaction txStart() {
        return ignite.transactions().txStart(TransactionConcurrency.PESSIMISTIC, TransactionIsolation.SERIALIZABLE);
    }
}