docs/user-manual/en/large-messages.md

# 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.  For JDBC persistence the `large-message-table` should be
configured.

```xml
<configuration xmlns="urn:activemq"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="urn:activemq /schema/artemis-server.xsd">
   <core xmlns="urn:activemq:core" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:activemq:core">
      ...
      <large-messages-directory>/data/large-messages</large-messages-directory>
      ...
   </core>
</configuration>
```

By default the large message directory is `data/largemessages` and
`large-message-table` is configured as "LARGE_MESSAGE_TABLE".

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

## Configuring the Client

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 URL
parameter `minLargeMessageSize`

> **Note:**
>
> 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.

[Configuring the transport directly from the client
side](configuring-transports.md#configuring-the-transport-directly-from-the-client)
will provide more information on how to instantiate the core session factory or
JMS connection factory.

## Compressed Large Messages

You can choose to send large messages in compressed form using
`compressLargeMessages` URL parameter.

If you specify the boolean URL parameter `compressLargeMessages` 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.

## Streaming large messages

Apache ActiveMQ Artemis 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.

### 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

To set the output stream when receiving a core message:

``` java
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
msg2.setOutputStream(someOtherOutputStream);
```

Set the input stream when sending a core message:

``` java
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 _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:

``` java
BytesMessage message = session.createBytesMessage();

FileInputStream fileInputStream = new FileInputStream(fileInput);

BufferedInputStream bufferedInput = new BufferedInputStream(fileInputStream);

message.setObjectProperty("JMS_AMQ_InputStream", bufferedInput);

someProducer.send(message);
```

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

``` java
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.

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

> **Note:**
>
> 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.

``` java
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.

``` java
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 [Large Message Example](examples.md#large-message) which shows
how large messages are configured and used with JMS.