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title: DataWeave Memory Management
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version: 2.11
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---

# DataWeave Memory Management

> For the full documentation index, see: https://docs.mulesoft.com/llms.txt

When processing large files through DataWeave in Mule runtime engine, there are a few things you can
set up to fine-tune how much memory will be used and when.

## RAM vs Disk Usage

DataWeave keeps small files in memory, but after a configurable threshold uses disk space to avoid
running out of memory. The created buffer files are placed in a default temporary directory. If you
want to store those files in a custom directory instead, you can specify the directory by using the
`java.io.tmpdir` property.

The buffer files remain in the temporary directory until the streams that reference the files are
closed. Closure normally occurs when flows complete their execution, so many buffer files in the
temporary folder can remain in use during long-running and concurrent executions.

Three types of DataWeave buffer files are generated:

- `dw-buffer-output-${count}.tmp`  
  Used to store the output of a transformation when the result is bigger than the threshold
  **1572864 bytes**. To change this threshold value, add the system property
  `com.mulesoft.dw.max_memory_allocation` and assign it the number of bytes you want as your new
  threshold. Mule runtime engine deletes the file when the value is no longer referenced, JVM GC
  collects it or when the Mule Event finishes executing.

- `dw-buffer-input-${count}.tmp`  
  Used to store the input of a transformation when it is bigger than the in-memory buffer, which is
  **1572864 bytes** by default. This is analogous to the `dw-buffer-output-${count}.tmp` file, but
  for input data.

- `dw-buffer-index-${count}.tmp`  
  Used to store index information of a value being read. This file helps DataWeave access data
  quickly. Mule runtime engine deletes the file when the execution of the transformation ends or, in
  a streaming use case like the foreach loop, when the stream ends (when foreach finishes its
  execution).

System properties:  
Because you can define system properties in several ways, see
[system properties](https://docs.mulesoft.com/mule-runtime/latest/configuring-properties#system-properties) for further
details.

- `com.mulesoft.dw.buffersize`  
  This system property determines the size in bytes of the in-memory input and output buffers used
  in DataWeave to keep the processed inputs and outputs. The default buffer size is 8192 bytes (8
  KB). This property receives a number (size in bytes), for example:
  `-Dcom.mulesoft.dw.buffersize=8192`.

- `com.mulesoft.dw.directbuffer.disable`  
  Introduced in Mule 4.2.2, this option controls whether DataWeave uses off-heap memory (the
  default) or heap memory. DataWeave uses off-heap memory for internal buffering. However, this
  setting can cause problems on machines that have only a small amount of memory. This property
  receives a boolean, for example: `-Dcom.mulesoft.dw.directbuffer.disable=true`.

- `com.mulesoft.dw.memory_pool_size`  
  Since Mule 4.3.0, DataWeave buffers use off-heap memory from a pool up to a defined size and
  allocates the rest using heap memory. This property determines the number of slots in the pool.
  The default number of slots is 60. This property receives a number (slots in the pool), for
  example: `-Dcom.mulesoft.dw.memory_pool_size=60`.

- `com.mulesoft.dw.max_memory_allocation`  
  Introduced in Mule 4.3.0, this property determines the maximum amount of memory to be used before
  it switches to disk. If a payload exceeds this size, it is stored in
  `dw-buffer-input-${count}.tmp` and `dw-buffer-output-${count}.tmp` temporary files. It also
  determines the size in bytes of each slot in the pool of off-heap memory. The default size is
  1572864 bytes (1.5 MB). This property receives a number (size in bytes), for example:
  `-Dcom.mulesoft.dw.max_memory_allocation=1572864`.

- `com.mulesoft.dw.buffer.memory.monitoring` (experimental)  
  Introduced in Mule 4.3.0, when this property is enabled, a message is logged each time a slot from
  the memory pool is taken or released. Note that it may be removed or change its behavior in future
  versions. This property receives a boolean, for example:
  `-Dcom.mulesoft.dw.buffer.memory.monitoring=true`.

- `mule.weave.script.parser.cache.size`  
  This system property determines the maximum size of compiled scripts that are being cached. The
  default value is 10.000.

- `com.mulesoft.dw.charbuffersize`  
  This system property determines the size (in bytes) of the buffer used by the writter. The default
  value is 4.096.

## See Also

- [DataWeave Scripts](https://docs.mulesoft.com/dataweave/2.11/dataweave-language-introduction)

- [DataWeave Selectors](https://docs.mulesoft.com/dataweave/2.11/dataweave-selectors)