ActiveMQ Artemis Documentation

Large Messages

Apache ActiveMQ Artemis 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, Apache ActiveMQ Artemis 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.

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:activemq"
   xsi:schemaLocation="urn:activemq /schema/artemis-server.xsd">

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.

Configuring Parameters

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 minLargeMessageSize


Apache ActiveMQ Artemis messages are encoded using 2 bytes per character so if the message data is filled with ASCII characters (which are 1 byte) the size of the resulting Apache ActiveMQ Artemis message would roughly double. This is important when calculating the size of a "large" message as it may appear to be less than the minLargeMessageSize before it is sent, but it then turns into a "large" message once it is encoded.

The default value is 100KiB.

Using Core API

If the Apache ActiveMQ Artemis Core API is used, the minimal large message size is specified by ServerLocator.setMinLargeMessageSize.

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

locator.setMinLargeMessageSize(25 * 1024);

ClientSessionFactory factory = ActiveMQClient.createClientSessionFactory();

Configuring the transport directly from the client side will provide more information on how to instantiate the session factory.

Using JMS

If JNDI is used to instantiate and look up the connection factory, the minimum large message size is configured in the JNDI context environment, e.g. Here's a simple example using the "ConnectionFactory" connection factory which is available in the context by default:


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

Compressed Large Messages

You can choose to send large messages in compressed form using compress-large-messages attributes.


If you specify the boolean property compressLargeMessages on the server locator or ConnectionFactory as true, The system will use the ZIP algorithm to compress the message body as the message is transferred to the server's side. Notice that there's no special treatment at the server's side, all the compressing and uncompressing is done at the client.

If the compressed size of a large message is below minLargeMessageSize, it is sent to server as regular messages. This means that the message won't be written into the server's large-message data directory, thus reducing the disk I/O.


If JNDI is used to instantiate and look up the connection factory, large message compression can be configured in the JNDI context environment, e.g. Here's a simple example using the "ConnectionFactory" connection factory which is available in the context by default:


Streaming large messages

Apache ActiveMQ Artemis supports setting the body of messages using input and output streams (

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 for sending messages or for receiving them.

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.

Name Description JMS Equivalent
setBodyInputStream(InputStream) Set the InputStream used to read a message body when sending it. JMS_AMQ_InputStream
setOutputStream(OutputStream) Set the OutputStream that will receive the body of a message. This method does not block. JMS_AMQ_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_AMQ_SaveStream

: org.apache.activemq.artemis.api.core.client.ClientMessage API

To set the output stream when receiving a core message:

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

// This will block here until the stream was transferred

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

// This will not wait the transfer to finish

Set the input stream when sending a core message:

ClientMessage msg = session.createMessage();

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 _AMQ_LARGE_SIZE.

Streaming over JMS

When using JMS, Apache ActiveMQ Artemis maps the streaming methods on the core API (see ClientMessage API table above) 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_AMQ_InputStream on messages being sent:

BytesMessage message = session.createBytesMessage();

FileInputStream fileInputStream = new FileInputStream(fileInput);

BufferedInputStream bufferedInput = new BufferedInputStream(fileInputStream);

message.setObjectProperty("JMS_AMQ_InputStream", bufferedInput);


The OutputStream can be set through the JMS Object Property JMS_AMQ_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_AMQ_SaveStream", bufferedOutput);

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

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


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

Streaming Alternative

If you choose not to use the InputStream or OutputStream capability of Apache ActiveMQ Artemis 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)
   // 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

Large message example

Please see the examples chapter for an example which shows how large message is configured and used with JMS.