Class HadoopSources
public final class HadoopSources extends Object
- Since:
- 3.0
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Field Summary
Fields Modifier and Type Field Description static String
COPY_ON_READ
With the new HDFS API, some of theRecordReader
s return the same key/value instances for each record, for exampleLineRecordReader
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Method Summary
Modifier and Type Method Description static <K, V> BatchSource<Map.Entry<K,V>>
inputFormat(org.apache.hadoop.conf.Configuration jobConf)
Convenience forinputFormat(Configuration, BiFunctionEx)
withMap.Entry
as its output type.static <K, V, E> BatchSource<E>
inputFormat(org.apache.hadoop.conf.Configuration configuration, BiFunctionEx<K,V,E> projectionFn)
Returns a source that reads records from Apache Hadoop HDFS and emits the results of transforming each record (a key-value pair) with the supplied projection function.
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Field Details
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COPY_ON_READ
With the new HDFS API, some of theRecordReader
s return the same key/value instances for each record, for exampleLineRecordReader
. If this property is set totrue
, the source makes a copy of each object after applying theprojectionFn
. For readers which create a new instance for each record, the source can be configured to not copy the objects for performance.Also if you are using a projection function which doesn't refer to any mutable state from the key or value, then it makes sense to set this property to
false
to avoid unnecessary copying.The source copies the objects by serializing and de-serializing them. The objects should be either
Writable
or serializable in a way which Jet can serialize/de-serialize.Here is how you can configure the source. Default and always safe value is
true
:Configuration conf = new Configuration(); conf.set(HadoopSources.COPY_ON_READ, "false"); BatchSource<Entry<K, V>> source = HadoopSources.inputFormat(conf);
- See Also:
- Constant Field Values
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Method Details
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inputFormat
@Nonnull public static <K, V, E> BatchSource<E> inputFormat(@Nonnull org.apache.hadoop.conf.Configuration configuration, @Nonnull BiFunctionEx<K,V,E> projectionFn)Returns a source that reads records from Apache Hadoop HDFS and emits the results of transforming each record (a key-value pair) with the supplied projection function.This source splits and balances the input data among Jet processors, doing its best to achieve data locality. To this end the Jet cluster topology should be aligned with Hadoop's — on each Hadoop member there should be a Jet member.
The processor will use either the new or the old MapReduce API based on the key which stores the
InputFormat
configuration. If it's stored under "mapreduce.job.inputformat.class", the new API will be used. Otherwise, the old API will be used. If you get the configuration fromJobContextImpl.getConfiguration()
, the new API will be used. Please seeCOPY_ON_READ
if you are using the new API.The default local parallelism for this processor is 2 (or less if less CPUs are available).
This source does not save any state to snapshot. If the job is restarted, all entries will be emitted again.
- Type Parameters:
K
- key type of the recordsV
- value type of the recordsE
- the type of the emitted value- Parameters:
configuration
- JobConf for reading files with the appropriate input format and pathprojectionFn
- function to create output objects from key and value. If the projection returns anull
for an item, that item will be filtered out
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inputFormat
@Nonnull public static <K, V> BatchSource<Map.Entry<K,V>> inputFormat(@Nonnull org.apache.hadoop.conf.Configuration jobConf)Convenience forinputFormat(Configuration, BiFunctionEx)
withMap.Entry
as its output type.
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