File based blocking queue is a simple java library, utilizes MappedByteBuffer to store and retrieve data. The functionality and complexity is comparable to LinkedBlockingQueue.

• Most recent update to the Queue will be in the file cache and hence an immediate read will be faster.

• Bigger the queue, we will have to do a seek (but sequential IO) to retrieve data in order.

• Removing am element is same as marking the data location for delete and skipping them while reading. (Hence atomic)

• The filesystem/space is split into multiple segments. Each segment is created on demand as the queue grows.

• The segments are recycled (To reduce the number of FD's in use) after the data is retrieved.

• Segments are discard instead of recycling if the max file system size has reached.

• Supports BlockingQueue API's.

• Note: There is (de-)Serialization overhead. When JVM exits or the system crashes the files are not in sync, hence we start with a new segments ignoring the old ones before the crash. The above can be solved by doing Periodic sync (not implemented by default).

    FileBackedBlockingQueue<String> queue = new FileBackedBlockingQueue.Builder<String>().directory(TEST_DIR).serializer(new StringSerializer()).build();
    for (int i = 0; i < 2000; i++)
        queue.add(TEST_STRING + i);

    (OR)

    FileBackedBlockingQueue<Runnable> workQueue = new FileBackedBlockingQueue.Builder<Runnable>().directory(dir).serializer(MessageTask.serializer).build();
    executor = new ThreadPoolExecutor(threadCount, threadCount, 60L, TimeUnit.SECONDS, workQueue);
    if (pattern.matcher(msgContainer.routingKey).matches())
        executor.execute(new MessageTask(msgContainer));