Read Hive Mapping#
readHibve mapping is a shortcut for reading from a Hive table or Hive view without explicitly creating a
Hive relation in Flowman.
mappings: measurements-raw: kind: readHive database: weather table: measurements columns: country: String air_temperature: Double filter: "country IS NOT NULL"
This would be equivalent to the following more verbose specification:
relations: measurements-raw: kind: hiveTable database: weather table: measurements mappings: measurements-raw: kind: readRelation relation: measurements-raw columns: country: String air_temperature: Double filter: "country IS NOT NULL"
The main scenario for using the shortcut is when reading from existing Hive tables, which are not managed by the
current Flowman project. Whenever you write to a Hive table within Flowman, you need to create the
anyway, so you should also use
readRelation in favor of
kind(mandatory) (type: string):
broadcast(optional) (type: boolean) (default: false): Hint for broadcasting the result of this mapping for map-side joins.
cache(optional) (type: string) (default: NONE): Cache mode for the results of this mapping. Supported values are
NONE- Disables caching of teh results of this mapping
DISK_ONLY- Caches the results on disk
MEMORY_ONLY- Caches the results in memory. If not enough memory is available, records will be uncached.
MEMORY_ONLY_SER- Caches the results in memory in a serialized format. If not enough memory is available, records will be uncached.
MEMORY_AND_DISK- Caches the results first in memory and then spills to disk.
MEMORY_AND_DISK_SER- Caches the results first in memory in a serialized format and then spills to disk.
database(mandatory) (string): Defines the Hive database where the table is defined. When no database is specified, the table is accessed without any specific qualification, meaning that the default database will be used.
table(mandatory) (string): Contains the name of the Hive table or Hive view.
columns(optional) (type: map:data_type) *(default: empty): Specifies the list of columns and types to read from the relation. This schema will be applied to the records after they have been read and interpreted by the underlying source. This schema will also be used as a substitute for schema inference and therefore can be very helpful when using
filter(optional) (type: string) (default: empty): An optional SQL filter expression that is applied for reading only a subset of records. The filter is applied after the schema as specified in
columnsis applied. This means that if you are using
columns, then you can only access these columns in the
main- the only output of the mapping