Does commitOffsets on high-level consumer block?

Question

In the Java Client (http://kafka.apache.org/documentation.html#highlevelconsumerapi), does commitOffsets on the high-level consumer block until offsets are successfully commited, or is it fire-and-forget?

Answer 1

Does commitOffsets on the high-level consumer block until offsets are successfully committed?

It looks like commitOffsets() loops through each consumer and calls updatePersistentPath if its offset has changed, and if so writes data via zkClient.writeData(path, getBytes(data)). It appears is though commitOffsets() does block until all the offsets are committed.

Here is the source code for commitOffsets() (ref):

public void commitOffsets() {
    if (zkClient == null) {
        logger.error("zk client is null. Cannot commit offsets");
        return;
    }
    for (Entry<String, Pool<Partition, PartitionTopicInfo>> e : topicRegistry.entrySet()) {
        ZkGroupTopicDirs topicDirs = new ZkGroupTopicDirs(config.getGroupId(), e.getKey());
        for (PartitionTopicInfo info : e.getValue().values()) {
            final long lastChanged = info.getConsumedOffsetChanged().get();
            if (lastChanged == 0) {
                logger.trace("consume offset not changed");
                continue;
            }
            final long newOffset = info.getConsumedOffset();
            //path: /consumers/<group>/offsets/<topic>/<brokerid-partition>
            final String path = topicDirs.consumerOffsetDir + "/" + info.partition.getName();
            try {
                ZkUtils.updatePersistentPath(zkClient, path, "" + newOffset);
            } catch (Throwable t) {
                logger.warn("exception during commitOffsets, path=" + path + ",offset=" + newOffset, t);
            } finally {
                info.resetComsumedOffsetChanged(lastChanged);
                if (logger.isDebugEnabled()) {
                    logger.debug("Committed [" + path + "] for topic " + info);
                }
            }
        }
    }
}

and for updatePersistentPath(...) (ref):

public static void updatePersistentPath(ZkClient zkClient, String path, String data) {
    try {
        zkClient.writeData(path, getBytes(data));
    } catch (ZkNoNodeException e) {
        createParentPath(zkClient, path);
        try {
            zkClient.createPersistent(path, getBytes(data));
        } catch (ZkNodeExistsException e2) {
            zkClient.writeData(path, getBytes(data));
        }
    }
}