druid/docs/development/extensions-core/orc.md

id	title
orc	ORC Extension

ORC extension

This Apache Druid extension enables Druid to ingest and understand the Apache ORC data format.

The extension provides the ORC input format and the ORC Hadoop parser for native batch ingestion and Hadoop batch ingestion, respectively. Please see corresponding docs for details.

To use this extension, make sure to include druid-orc-extensions.

Migration from 'contrib' extension

This extension, first available in version 0.15.0, replaces the previous 'contrib' extension which was available until 0.14.0-incubating. While this extension can index any data the 'contrib' extension could, the JSON spec for the ingestion task is incompatible, and will need modified to work with the newer 'core' extension.

To migrate to 0.15.0+:

• In inputSpec of ioConfig, inputFormat must be changed from "org.apache.hadoop.hive.ql.io.orc.OrcNewInputFormat" to "org.apache.orc.mapreduce.OrcInputFormat"
• The 'contrib' extension supported a typeString property, which provided the schema of the ORC file, of which was essentially required to have the types correct, but notably not the column names, which facilitated column renaming. In the 'core' extension, column renaming can be achieved with flattenSpec. For example, "typeString":"struct<time:string,name:string>" with the actual schema struct<_col0:string,_col1:string>, to preserve Druid schema would need replaced with:

"flattenSpec": {
  "fields": [
    {
      "type": "path",
      "name": "time",
      "expr": "$._col0"
    },
    {
      "type": "path",
      "name": "name",
      "expr": "$._col1"
    }
  ]
  ...
}

• The 'contrib' extension supported a mapFieldNameFormat property, which provided a way to specify a dimension to flatten OrcMap columns with primitive types. This functionality has also been replaced with flattenSpec. For example: "mapFieldNameFormat": "<PARENT>_<CHILD>" for a dimension nestedData_dim1, to preserve Druid schema could be replaced with

"flattenSpec": {
 "fields": [
   {
     "type": "path",
     "name": "nestedData_dim1",
     "expr": "$.nestedData.dim1"
   }
 ]
 ...
}