# Convert input data format in Amazon Data Firehose
Amazon Data Firehose can convert the format of your input data from JSON to [Apache Parquet](https://parquet.apache.org/) or [Apache ORC](https://orc.apache.org/) before storing the data in Amazon S3. Parquet and ORC are columnar data formats that save space and enable faster queries compared to row-oriented formats like JSON. If you want to convert an input format other than JSON, such as comma-separated values (CSV) or structured text, you can use AWS Lambda to transform it to JSON first. For more information, see [Transform source data in Amazon Data Firehose](data-transformation.md).
You can convert the format of your data even if you aggregate your records before sending them to Amazon Data Firehose.
Amazon Data Firehose requires the following three elements to convert the format of your record data:
## Deserializer
Amazon Data Firehose requires a deserializer to read the JSON of your input data. You can choose one of the following two types of deserializer.
When combining multiple JSON documents into the same record, make sure that your input is still presented in the supported JSON format. An array of JSON documents is not a valid input.
For example, this is the correct input: `{"a": 1}{"b": 1}` and this is the incorrect input: `[{"a":1}, {"a":2}]`.
+ [Apache Hive JSON SerDe](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-JSON)
+ [OpenX JSON SerDe](https://github.com/rcongiu/Hive-JSON-Serde)
### Choose the JSON deserializer
Choose the [OpenX JSON SerDe](https://github.com/rcongiu/Hive-JSON-Serde) if your input JSON contains time stamps in the following formats:
+ yyyy-MM-dd'T'HH:mm:ss[.S]'Z', where the fraction can have up to 9 digits – For example, `2017-02-07T15:13:01.39256Z`.
+ yyyy-[M]M-[d]d HH:mm:ss[.S], where the fraction can have up to 9 digits – For example, `2017-02-07 15:13:01.14`.
+ Epoch seconds – For example, `1518033528`.
+ Epoch milliseconds – For example, `1518033528123`.
+ Floating point epoch seconds – For example, `1518033528.123`.
The OpenX JSON SerDe can convert periods (`.`) to underscores (`_`). It can also convert JSON keys to lowercase before deserializing them. For more information about the options that are available with this deserializer through Amazon Data Firehose, see [OpenXJsonSerDe](https://docs.aws.amazon.com/firehose/latest/APIReference/API_OpenXJsonSerDe.html).
If you're not sure which deserializer to choose, use the OpenX JSON SerDe, unless you have time stamps that it doesn't support.
If you have time stamps in formats other than those listed previously, use the [Apache Hive JSON SerDe](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+DDL#LanguageManualDDL-JSON). When you choose this deserializer, you can specify the time stamp formats to use. To do this, follow the pattern syntax of the Joda-Time `DateTimeFormat` format strings. For more information, see [Class DateTimeFormat](https://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormat.html).
You can also use the special value `millis` to parse time stamps in epoch milliseconds. If you don't specify a format, Amazon Data Firehose uses `java.sql.Timestamp::valueOf` by default.
The Hive JSON SerDe doesn't allow the following:
+ Periods (`.`) in column names.
+ Fields whose type is `uniontype`.
+ Fields that have numerical types in the schema, but that are strings in the JSON. For example, if the schema is (an int), and the JSON is `{"a":"123"}`, the Hive SerDe gives an error.
The Hive SerDe doesn't convert nested JSON into strings. For example, if you have `{"a":{"inner":1}}`, it doesn't treat `{"inner":1}` as a string.
## Schema
Amazon Data Firehose requires a schema to determine how to interpret that data. Use [AWS Glue](https://docs.aws.amazon.com/glue/latest/dg/what-is-glue.html) to create a schema in the AWS Glue Data Catalog. Amazon Data Firehose then references that schema and uses it to interpret your input data. You can use the same schema to configure both Amazon Data Firehose and your analytics software. For more information, see [Populating the AWS Glue Data Catalog](https://docs.aws.amazon.com/glue/latest/dg/populate-data-catalog.html) in the *AWS Glue Developer Guide*.
**Note**
The schema created in AWS Glue Data Catalog should match the input data structure. Otherwise, the converted data will not contain attributes that are not specified in the schema. If you use nested JSON, use a STRUCT type in the schema that mirrors the structure of your JSON data. See [this example](https://docs.aws.amazon.com/athena/latest/ug/openx-json-serde.html#nested-json-serde-example) for how to handle nested JSON with a STRUCT type.
**Important**
For data types that do not specify a size limit, there is a practical limit of 32 MBs for all of the data in a single row.
If you specify length for `CHAR` or `VARCHAR`, Firehose truncates the strings at the specified length when it reads the input data. If the underlying data string is longer, it remains unchanged.
## Serializer
**Firehose requires a serializer to convert the data to the target columnar storage format (Parquet or ORC)** – You can choose one of the following two types of serializers.
+ [ORC SerDe](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+ORC)
+ [Parquet SerDe](https://cwiki.apache.org/confluence/display/Hive/Parquet)
### Choose the serializer
The serializer that you choose depends on your business needs. To learn more about the two serializer options, see [ORC SerDe](https://cwiki.apache.org/confluence/display/Hive/LanguageManual+ORC) and [Parquet SerDe](https://cwiki.apache.org/confluence/display/Hive/Parquet).