Package org.apache.zookeeper.server.quorum

Class CommitProcessor

  • All Implemented Interfaces:
    Runnable, RequestProcessor
    public class CommitProcessor
extends ZooKeeperCriticalThread
implements RequestProcessor
    This RequestProcessor matches the incoming committed requests with the locally submitted requests. The trick is that locally submitted requests that change the state of the system will come back as incoming committed requests, so we need to match them up. Instead of just waiting for the committed requests, we process the uncommitted requests that belong to other sessions. The CommitProcessor is multi-threaded. Communication between threads is handled via queues, atomics, and wait/notifyAll synchronized on the processor. The CommitProcessor acts as a gateway for allowing requests to continue with the remainder of the processing pipeline. It will allow many read requests but only a single write request to be in flight simultaneously, thus ensuring that write requests are processed in transaction id order. - 1 commit processor main thread, which watches the request queues and assigns requests to worker threads based on their sessionId so that read and write requests for a particular session are always assigned to the same thread (and hence are guaranteed to run in order). - 0-N worker threads, which run the rest of the request processor pipeline on the requests. If configured with 0 worker threads, the primary commit processor thread runs the pipeline directly. Typical (default) thread counts are: on a 32 core machine, 1 commit processor thread and 32 worker threads. Multi-threading constraints: - Each session's requests must be processed in order. - Write requests must be processed in zxid order - Must ensure no race condition between writes in one session that would trigger a watch being set by a read request in another session The current implementation solves the third constraint by simply allowing no read requests to be processed in parallel with write requests.

    • Field Detail

      • ZOOKEEPER_COMMIT_PROC_NUM_WORKER_THREADS

        public static final String ZOOKEEPER_COMMIT_PROC_NUM_WORKER_THREADS
        Default: numCores
        See Also:
        Constant Field Values

      • ZOOKEEPER_COMMIT_PROC_SHUTDOWN_TIMEOUT

        public static final String ZOOKEEPER_COMMIT_PROC_SHUTDOWN_TIMEOUT
        Default worker pool shutdown timeout in ms: 5000 (5s)
        See Also:
        Constant Field Values

      • ZOOKEEPER_COMMIT_PROC_MAX_READ_BATCH_SIZE

        public static final String ZOOKEEPER_COMMIT_PROC_MAX_READ_BATCH_SIZE
        Default max read batch size: -1 to disable the feature
        See Also:
        Constant Field Values

      • ZOOKEEPER_COMMIT_PROC_MAX_COMMIT_BATCH_SIZE

        public static final String ZOOKEEPER_COMMIT_PROC_MAX_COMMIT_BATCH_SIZE
        Default max commit batch size: 1
        See Also:
        Constant Field Values

      • queuedWriteRequests

        protected final LinkedBlockingQueue<Request> queuedWriteRequests
        Incoming requests that are waiting on a commit, contained in order of arrival

      • pendingRequests

        protected final Map<Long,​Deque<Request>> pendingRequests
        Requests that we are holding until commit comes in. Keys represent session ids, each value is a linked list of the session's requests.

      • numRequestsProcessing

        protected final AtomicInteger numRequestsProcessing
        The number of requests currently being processed

      • stoppedMainLoop

        protected volatile boolean stoppedMainLoop
        For testing purposes, we use a separated stopping condition for the outer loop.

      • stopped

        protected volatile boolean stopped

    • Method Detail

      • needCommit

        protected boolean needCommit​(Request request)

      • run

        public void run()
        Specified by:
        run in interface Runnable
        Overrides:
        run in class Thread

      • endOfIteration

        protected void endOfIteration()

      • start

        public void start()
        Overrides:
        start in class Thread

      • getMaxReadBatchSize

        public static int getMaxReadBatchSize()

      • getMaxCommitBatchSize

        public static int getMaxCommitBatchSize()

      • setMaxReadBatchSize

        public static void setMaxReadBatchSize​(int size)

      • setMaxCommitBatchSize

        public static void setMaxCommitBatchSize​(int size)

      • commit

        public void commit​(Request request)