# Transform source data in Amazon Data Firehose
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Amazon Data Firehose can invoke your Lambda function to transform incoming source data and deliver the transformed data to destinations. You can enable Amazon Data Firehose data transformation when you create your Firehose stream.

## Understand data transformation flow
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When you enable Firehose data transformation, Firehose buffers incoming data. The buffering size hint ranges between 0.2 MB and 3MB. The default Lambda buffering size hint is 1 MB for all destinations, except Splunk and Snowflake. For Splunk and Snowflake, the default buffering hint is 256 KB. The Lambda buffering interval hint ranges between 0 and 900 seconds. The default Lambda buffering interval hint is sixty seconds for all destinations except Snowflake. For Snowflake, the default buffering hint interval is 30 seconds. To adjust the buffering size, set the [ProcessingConfiguration](https://docs.amazonaws.cn/firehose/latest/APIReference/API_ProcessingConfiguration.html) parameter of the [CreateDeliveryStream](https://docs.amazonaws.cn/firehose/latest/APIReference/API_CreateDeliveryStream.html) or [UpdateDestination](https://docs.amazonaws.cn/firehose/latest/APIReference/API_UpdateDestination.html) API with the [ProcessorParameter](https://docs.amazonaws.cn/firehose/latest/APIReference/API_ProcessorParameter.html) called `BufferSizeInMBs` and `IntervalInSeconds`. Firehose then invokes the specified Lambda function synchronously with each buffered batch using the Amazon Lambda synchronous invocation mode. The transformed data is sent from Lambda to Firehose. Firehose then sends it to the destination when the specified destination buffering size or buffering interval is reached, whichever happens first.

**Important**  
The Lambda synchronous invocation mode has a payload size limit of 6 MB for both the request and the response. Make sure that your buffering size for sending the request to the function is less than or equal to 6 MB. Also ensure that the response that your function returns doesn't exceed 6 MB.

## Lambda invocation duration
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Amazon Data Firehose supports a Lambda invocation time of up to 5 minutes. If your Lambda function takes more than 5 minutes to complete, you get the following error: Firehose encountered timeout errors when calling Amazon Lambda. The maximum supported function timeout is 5 minutes.

For information about what Amazon Data Firehose does if such an error occurs, see [Handle failure in data transformation](data-transformation-failure-handling.md).