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## Chapter 23. Large Messages

HornetQ supports sending and receiving of huge messages, even when the client and server are running with limited memory. The only realistic limit to the size of a message that can be sent or consumed is the amount of disk space you have available. We have tested sending and consuming messages up to 8 GiB in size with a client and server running in just 50MiB of RAM!

To send a large message, the user can set an `InputStream` on a message body, and when that message is sent, HornetQ will read the `InputStream`. A `FileInputStream` could be used for example to send a huge message from a huge file on disk.

As the `InputStream` is read the data is sent to the server as a stream of fragments. The server persists these fragments to disk as it receives them and when the time comes to deliver them to a consumer they are read back of the disk, also in fragments and sent down the wire. When the consumer receives a large message it initially receives just the message with an empty body, it can then set an `OutputStream` on the message to stream the huge message body to a file on disk or elsewhere. At no time is the entire message body stored fully in memory, either on the client or the server.

## 23.1. Configuring the server

Large messages are stored on a disk directory on the server side, as configured on the main configuration file.

The configuration property `large-messages-directory` specifies where large messages are stored.

    <configuration xmlns="urn:hornetq"
                   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
                   xsi:schemaLocation="urn:hornetq /schema/hornetq-configuration.xsd">

    ...

    <large-messages-directory>/data/large-messages</large-messages-directory>

    ...

    </configuration

By default the large message directory is `data/largemessages`

For the best performance we recommend large messages directory is stored on a different physical volume to the message journal or paging directory.

## 23.2. Setting the limits

Any message larger than a certain size is considered a large message. Large messages will be split up and sent in fragments. This is determined by the parameter `min-large-message-size`

The default value is 100KiB.

### 23.2.1. Using Core API

If the HornetQ Core API is used, the minimal large message size is specified by `ClientSessionFactory.setMinLargeMessageSize`.

    ServerLocator locator = HornetQClient.createServerLocatorWithoutHA(new TransportConfiguration(NettyConnectorFactory.class.getName()))

    locator.setMinLargeMessageSize(25 * 1024);

    ClientSessionFactory factory = HornetQClient.createClientSessionFactory();

Section 16.3, “Configuring the transport directly from the client side.” will provide more information on how to instantiate the session factory.

### 23.2.2. Using JMS

If JNDI is used to look up the connection factory, the minimum large message size is specified in `hornetq-jms.xml`

    ...
    <connection-factory name="ConnectionFactory">
    <connectors>
       <connector-ref connector-name="netty"/>
    </connectors>
    <entries>
       <entry name="ConnectionFactory"/>
       <entry name="XAConnectionFactory"/>
    </entries>

    <min-large-message-size>250000</min-large-message-size>
    </connection-factory>
    ...

If the connection factory is being instantiated directly, the minimum large message size is specified by `HornetQConnectionFactory.setMinLargeMessageSize`.

## 23.3. Streaming large messages

HornetQ supports setting the body of messages using input and output streams (`java.lang.io`)

These streams are then used directly for sending (input streams) and receiving (output streams) messages.

When receiving messages there are 2 ways to deal with the output stream; you may choose to block while the output stream is recovered using the method `ClientMessage.saveOutputStream` or alternatively using the method `ClientMessage.setOutputstream` which will asynchronously write the message to the stream. If you choose the latter the consumer must be kept alive until the message has been fully received.

You can use any kind of stream you like. The most common use case is to send files stored in your disk, but you could also send things like JDBC Blobs, `SocketInputStream`, things you recovered from `HTTPRequests` etc. Anything as long as it implements `java.io.InputStream` for sending messages or `java.io.OutputStream` for receiving them.

### 23.3.1. Streaming over Core API

The following table shows a list of methods available at `ClientMessage` which are also available through JMS by the use of object properties.

Table 23.1. org.hornetq.api.core.client.ClientMessage API

Name | Description | JMS Equivalent Property
--- | --- | ---
setBodyInputStream(InputStream) | Set the InputStream used to read a message body when sending it. | JMS_HQ_InputStream
setOutputStream(OutputStream) | Set the OutputStream that will receive the body of a message. This method does not block. | JMS_HQ_OutputStream
saveOutputStream(OutputStream) | Save the body of the message to the `OutputStream`. It will block until the entire content is transferred to the `OutputStream`. | JMS_HQ_SaveStream

To set the output stream when receiving a core message:

    ...
    ClientMessage msg = consumer.receive(...);

    // This will block here until the stream was transferred
    msg.saveOutputStream(someOutputStream);

    ClientMessage msg2 = consumer.receive(...);

    // This will not wait the transfer to finish
    msg.setOutputStream(someOtherOutputStream);
    ...

Set the input stream when sending a core message:

    ...
    ClientMessage msg = session.createMessage();
    msg.setInputStream(dataInputStream);
    ...

Notice also that for messages with more than 2GiB the getBodySize() will return invalid values since this is an integer (which is also exposed to the JMS API). On those cases you can use the message property _HQ_LARGE_SIZE.

### 23.3.2. Streaming over JMS

When using JMS, HornetQ maps the streaming methods on the core API (see Table 23.1, “org.hornetq.api.core.client.ClientMessage API”) by setting object properties . You can use the method `Message.setObjectProperty` to set the input and output streams.

The `InputStream` can be defined through the JMS Object Property JMS_HQ_InputStream on messages being sent:

    BytesMessage message = session.createBytesMessage();

    FileInputStream fileInputStream = new FileInputStream(fileInput);

    BufferedInputStream bufferedInput = new BufferedInputStream(fileInputStream);

    message.setObjectProperty("JMS_HQ_InputStream", bufferedInput);

    someProducer.send(message);

The `OutputStream` can be set through the JMS Object Property JMS_HQ_SaveStream on messages being received in a blocking way.

    BytesMessage messageReceived = (BytesMessage)messageConsumer.receive(120000);

    File outputFile = new File("huge_message_received.dat");

    FileOutputStream fileOutputStream = new FileOutputStream(outputFile);

    BufferedOutputStream bufferedOutput = new BufferedOutputStream(fileOutputStream);

    // This will block until the entire content is saved on disk
    messageReceived.setObjectProperty("JMS_HQ_SaveStream", bufferedOutput);

Setting the `OutputStream` could also be done in a non blocking way using the property JMS_HQ_OutputStream.

    // This won't wait the stream to finish. You need to keep the consumer active.
    messageReceived.setObjectProperty("JMS_HQ_OutputStream", bufferedOutput);

## Note

When using JMS, Streaming large messages are only supported on `StreamMessage` and `BytesMessage`.

## 23.4. Streaming Alternative

If you choose not to use the `InputStream` or `OutputStream` capability of HornetQ You could still access the data directly in an alternative fashion.

On the Core API just get the bytes of the body as you normally would.

    ClientMessage msg = consumer.receive();

    byte[] bytes = new byte[1024];
    for (int i = 0 ;  i < msg.getBodySize(); i += bytes.length)
    {
       msg.getBody().readBytes(bytes);
       // Whatever you want to do with the bytes
    }

If using JMS API, `BytesMessage` and `StreamMessage` also supports it transparently.

    BytesMessage rm = (BytesMessage)cons.receive(10000);

    byte data[] = new byte[1024];

    for (int i = 0; i < rm.getBodyLength(); i += 1024)
    {
       int numberOfBytes = rm.readBytes(data);
       // Do whatever you want with the data
    }

## 23.5. Cache Large Messages on client

Large messages are transferred by streaming from server to client. The message is broken into smaller packets and as the message is read more packets will be received. Because of that the body of the large message can be read only once, and by consequence a received message can be sent to another producer only once. The JMS Bridge for instance won't be able to resend a large message in case of failure

To solve this problem, you can enable the property `cache-large-message-client` on the connection factory. If you enable this property the client consumer will create a temporary file to hold the large message content, so it would be possible to resend large messages.

## Note

Use this option on the connection factory used by the JMS Bridge if the JMS Bridge is being used for large messages.

## 23.6. Large message example

Please see Section 11.1.29, “Large Message” for an example which shows how large message is configured and used with JMS.

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