/**
   * Check how prefetch override works.
   *
   * @throws Exception IF failed.
   */
  public void testOpenPrefetchOverride() throws Exception {
    create(igfsSecondary, paths(DIR, SUBDIR), paths(FILE));

    // Write enough data to the secondary file system.
    final int blockSize = IGFS_BLOCK_SIZE;

    IgfsOutputStream out = igfsSecondary.append(FILE, false);

    int totalWritten = 0;

    while (totalWritten < blockSize * 2 + chunk.length) {
      out.write(chunk);

      totalWritten += chunk.length;
    }

    out.close();

    awaitFileClose(igfsSecondary.asSecondary(), FILE);

    // Instantiate file system with overridden "seq reads before prefetch" property.
    Configuration cfg = new Configuration();

    cfg.addResource(U.resolveIgniteUrl(PRIMARY_CFG));

    int seqReads = SEQ_READS_BEFORE_PREFETCH + 1;

    cfg.setInt(String.format(PARAM_IGFS_SEQ_READS_BEFORE_PREFETCH, "igfs:grid@"), seqReads);

    FileSystem fs = FileSystem.get(new URI(PRIMARY_URI), cfg);

    // Read the first two blocks.
    Path fsHome = new Path(PRIMARY_URI);
    Path dir = new Path(fsHome, DIR.name());
    Path subdir = new Path(dir, SUBDIR.name());
    Path file = new Path(subdir, FILE.name());

    FSDataInputStream fsIn = fs.open(file);

    final byte[] readBuf = new byte[blockSize * 2];

    fsIn.readFully(0, readBuf, 0, readBuf.length);

    // Wait for a while for prefetch to finish (if any).
    IgfsMetaManager meta = igfs.context().meta();

    IgfsFileInfo info = meta.info(meta.fileId(FILE));

    IgfsBlockKey key = new IgfsBlockKey(info.id(), info.affinityKey(), info.evictExclude(), 2);

    IgniteCache<IgfsBlockKey, byte[]> dataCache =
        igfs.context().kernalContext().cache().jcache(igfs.configuration().getDataCacheName());

    for (int i = 0; i < 10; i++) {
      if (dataCache.containsKey(key)) break;
      else U.sleep(100);
    }

    fsIn.close();

    // Remove the file from the secondary file system.
    igfsSecondary.delete(FILE, false);

    // Try reading the third block. Should fail.
    GridTestUtils.assertThrows(
        log,
        new Callable<Object>() {
          @Override
          public Object call() throws Exception {
            IgfsInputStream in0 = igfs.open(FILE);

            in0.seek(blockSize * 2);

            try {
              in0.read(readBuf);
            } finally {
              U.closeQuiet(in0);
            }

            return null;
          }
        },
        IOException.class,
        "Failed to read data due to secondary file system exception: /dir/subdir/file");
  }
  /**
   * @param cacheMode Cache mode.
   * @param sameAff If {@code false} uses different number of partitions for caches.
   * @param concurrency Transaction concurrency.
   * @param isolation Transaction isolation.
   * @throws Exception If failed.
   */
  private void crossCacheTxFailover(
      CacheMode cacheMode,
      boolean sameAff,
      final TransactionConcurrency concurrency,
      final TransactionIsolation isolation)
      throws Exception {
    IgniteKernal ignite0 = (IgniteKernal) ignite(0);

    final AtomicBoolean stop = new AtomicBoolean();

    try {
      ignite0.createCache(cacheConfiguration(CACHE1, cacheMode, 256));
      ignite0.createCache(cacheConfiguration(CACHE2, cacheMode, sameAff ? 256 : 128));

      final AtomicInteger threadIdx = new AtomicInteger();

      IgniteInternalFuture<?> fut =
          GridTestUtils.runMultiThreadedAsync(
              new Callable<Void>() {
                @Override
                public Void call() throws Exception {
                  int idx = threadIdx.getAndIncrement();

                  Ignite ignite = ignite(idx % GRID_CNT);

                  log.info(
                      "Started update thread [node="
                          + ignite.name()
                          + ", client="
                          + ignite.configuration().isClientMode()
                          + ']');

                  IgniteCache<TestKey, TestValue> cache1 = ignite.cache(CACHE1);
                  IgniteCache<TestKey, TestValue> cache2 = ignite.cache(CACHE2);

                  assertNotSame(cache1, cache2);

                  IgniteTransactions txs = ignite.transactions();

                  ThreadLocalRandom rnd = ThreadLocalRandom.current();

                  long iter = 0;

                  while (!stop.get()) {
                    boolean sameKey = rnd.nextBoolean();

                    try {
                      try (Transaction tx = txs.txStart(concurrency, isolation)) {
                        if (sameKey) {
                          TestKey key = new TestKey(rnd.nextLong(KEY_RANGE));

                          cacheOperation(rnd, cache1, key);
                          cacheOperation(rnd, cache2, key);
                        } else {
                          TestKey key1 = new TestKey(rnd.nextLong(KEY_RANGE));
                          TestKey key2 = new TestKey(key1.key() + 1);

                          cacheOperation(rnd, cache1, key1);
                          cacheOperation(rnd, cache2, key2);
                        }

                        tx.commit();
                      }
                    } catch (CacheException | IgniteException e) {
                      log.info("Update error: " + e);
                    }

                    if (iter++ % 500 == 0) log.info("Iteration: " + iter);
                  }

                  return null;
                }

                /**
                 * @param rnd Random.
                 * @param cache Cache.
                 * @param key Key.
                 */
                private void cacheOperation(
                    ThreadLocalRandom rnd, IgniteCache<TestKey, TestValue> cache, TestKey key) {
                  switch (rnd.nextInt(4)) {
                    case 0:
                      cache.put(key, new TestValue(rnd.nextLong()));

                      break;

                    case 1:
                      cache.remove(key);

                      break;

                    case 2:
                      cache.invoke(key, new TestEntryProcessor(rnd.nextBoolean() ? 1L : null));

                      break;

                    case 3:
                      cache.get(key);

                      break;

                    default:
                      assert false;
                  }
                }
              },
              10,
              "tx-thread");

      long stopTime = System.currentTimeMillis() + 3 * 60_000;

      long topVer = ignite0.cluster().topologyVersion();

      boolean failed = false;

      while (System.currentTimeMillis() < stopTime) {
        log.info("Start node.");

        IgniteKernal ignite = (IgniteKernal) startGrid(GRID_CNT);

        assertFalse(ignite.configuration().isClientMode());

        topVer++;

        IgniteInternalFuture<?> affFut =
            ignite
                .context()
                .cache()
                .context()
                .exchange()
                .affinityReadyFuture(new AffinityTopologyVersion(topVer));

        try {
          if (affFut != null) affFut.get(30_000);
        } catch (IgniteFutureTimeoutCheckedException e) {
          log.error("Failed to wait for affinity future after start: " + topVer);

          failed = true;

          break;
        }

        Thread.sleep(500);

        log.info("Stop node.");

        stopGrid(GRID_CNT);

        topVer++;

        affFut =
            ignite0
                .context()
                .cache()
                .context()
                .exchange()
                .affinityReadyFuture(new AffinityTopologyVersion(topVer));

        try {
          if (affFut != null) affFut.get(30_000);
        } catch (IgniteFutureTimeoutCheckedException e) {
          log.error("Failed to wait for affinity future after stop: " + topVer);

          failed = true;

          break;
        }
      }

      stop.set(true);

      fut.get();

      assertFalse("Test failed, see log for details.", failed);
    } finally {
      stop.set(true);

      ignite0.destroyCache(CACHE1);
      ignite0.destroyCache(CACHE2);

      awaitPartitionMapExchange();
    }
  }