cascading.tap.hadoop
Class PartitionTap
java.lang.Object
cascading.tap.Tap<Config,Input,Output>
cascading.tap.partition.BasePartitionTap<JobConf,RecordReader,OutputCollector>
cascading.tap.hadoop.PartitionTap
- All Implemented Interfaces:
- FlowElement, Traceable, Serializable
public class PartitionTap
- extends BasePartitionTap<JobConf,RecordReader,OutputCollector>
Class PartitionTap can be used to write tuple streams out to files and sub-directories based on the values in the
current Tuple
instance.
The constructor takes a Hfs
Tap
and a Partition
implementation. This allows Tuple values at given positions to be used as directory names during write
operations, and directory names as data during read operations.
The key value here is that there is no need to duplicate data values in the directory names and inside
the data files.
So only values declared in the parent Tap will be read or written to the underlying file system files. But
fields declared by the Partition
will only be read or written to the directory names. That is, the
PartitionTap instance will sink or source the partition fields, plus the parent Tap fields. The partition
fields and parent Tap fields do not need to have common field names.
Note that Hadoop can only sink to directories, and all files in those directories are "part-xxxxx" files.
openWritesThreshold
limits the number of open files to be output to. This value defaults to 300 files.
Each time the threshold is exceeded, 10% of the least recently used open files will be closed.
PartitionTap will populate a given partition
without regard to case of the values being used. Thus
the resulting paths 2012/June/
and 2012/june/
will likely result in two open files into the same
location. Forcing the case to be consistent with a custom Partition implementation or an upstream
Function
is recommended, see ExpressionFunction
.
Though Hadoop has no mechanism to prevent simultaneous writes to a directory from multiple jobs, it doesn't mean
its safe to do so. Same is true with the PartitionTap. Interleaving writes to a common parent (root) directory
across multiple flows will very likely lead to data loss.
- See Also:
- Serialized Form
Constructor Summary |
PartitionTap(Hfs parent,
Partition partition)
Constructor PartitionTap creates a new PartitionTap instance using the given parent Hfs Tap as the
base path and default Scheme , and the partition. |
PartitionTap(Hfs parent,
Partition partition,
int openWritesThreshold)
Constructor PartitionTap creates a new PartitionTap instance using the given parent Hfs Tap as the
base path and default Scheme , and the partition. |
PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode)
Constructor PartitionTap creates a new PartitionTap instance using the given parent Hfs Tap as the
base path and default Scheme , and the partition. |
PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode,
boolean keepParentOnDelete)
Constructor PartitionTap creates a new PartitionTap instance using the given parent Hfs Tap as the
base path and default Scheme , and the partition. |
PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode,
boolean keepParentOnDelete,
int openWritesThreshold)
Constructor PartitionTap creates a new PartitionTap instance using the given parent Hfs Tap as the
base path and default Scheme , and the partition. |
Methods inherited from class cascading.tap.partition.BasePartitionTap |
commitResource, createResource, deleteResource, equals, getChildPartitionIdentifiers, getIdentifier, getModifiedTime, getOpenWritesThreshold, getParent, getPartition, hashCode, openForWrite, prepareResourceForRead, prepareResourceForWrite, resourceExists, rollbackResource, toString |
Methods inherited from class cascading.tap.Tap |
createResource, deleteResource, flowConfInit, getConfigDef, getFullIdentifier, getFullIdentifier, getModifiedTime, getScheme, getSinkFields, getSinkMode, getSourceFields, getStepConfigDef, getTrace, hasConfigDef, hasStepConfigDef, id, isEquivalentTo, isKeep, isReplace, isSink, isSource, isTemporary, isUpdate, openForRead, openForWrite, outgoingScopeFor, presentSinkFields, presentSourceFields, resolveIncomingOperationArgumentFields, resolveIncomingOperationPassThroughFields, resourceExists, retrieveSinkFields, retrieveSourceFields, setScheme, sinkConfInit, taps |
PartitionTap
@ConstructorProperties(value={"parent","partition"})
public PartitionTap(Hfs parent,
Partition partition)
- Constructor PartitionTap creates a new PartitionTap instance using the given parent
Hfs
Tap as the
base path and default Scheme
, and the partition.
- Parameters:
parent
- of type Tappartition
- of type String
PartitionTap
@ConstructorProperties(value={"parent","partition","openWritesThreshold"})
public PartitionTap(Hfs parent,
Partition partition,
int openWritesThreshold)
- Constructor PartitionTap creates a new PartitionTap instance using the given parent
Hfs
Tap as the
base path and default Scheme
, and the partition.
openWritesThreshold
limits the number of open files to be output to.
- Parameters:
parent
- of type Hfspartition
- of type StringopenWritesThreshold
- of type int
PartitionTap
@ConstructorProperties(value={"parent","partition","sinkMode"})
public PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode)
- Constructor PartitionTap creates a new PartitionTap instance using the given parent
Hfs
Tap as the
base path and default Scheme
, and the partition.
- Parameters:
parent
- of type Tappartition
- of type StringsinkMode
- of type SinkMode
PartitionTap
@ConstructorProperties(value={"parent","partition","sinkMode","keepParentOnDelete"})
public PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode,
boolean keepParentOnDelete)
- Constructor PartitionTap creates a new PartitionTap instance using the given parent
Hfs
Tap as the
base path and default Scheme
, and the partition.
keepParentOnDelete
, when set to true, prevents the parent Tap from being deleted when BasePartitionTap.deleteResource(Object)
is called, typically an issue when used inside a Cascade
.
- Parameters:
parent
- of type Tappartition
- of type StringsinkMode
- of type SinkModekeepParentOnDelete
- of type boolean
PartitionTap
@ConstructorProperties(value={"parent","partition","sinkMode","keepParentOnDelete","openWritesThreshold"})
public PartitionTap(Hfs parent,
Partition partition,
SinkMode sinkMode,
boolean keepParentOnDelete,
int openWritesThreshold)
- Constructor PartitionTap creates a new PartitionTap instance using the given parent
Hfs
Tap as the
base path and default Scheme
, and the partition.
keepParentOnDelete
, when set to true, prevents the parent Tap from being deleted when BasePartitionTap.deleteResource(Object)
is called, typically an issue when used inside a Cascade
.
openWritesThreshold
limits the number of open files to be output to.
- Parameters:
parent
- of type Tappartition
- of type StringsinkMode
- of type SinkModekeepParentOnDelete
- of type booleanopenWritesThreshold
- of type int
createTupleEntrySchemeCollector
protected TupleEntrySchemeCollector createTupleEntrySchemeCollector(FlowProcess<JobConf> flowProcess,
Tap parent,
String path,
long sequence)
throws IOException
- Specified by:
createTupleEntrySchemeCollector
in class BasePartitionTap<JobConf,RecordReader,OutputCollector>
- Throws:
IOException
createTupleEntrySchemeIterator
protected TupleEntrySchemeIterator createTupleEntrySchemeIterator(FlowProcess<JobConf> flowProcess,
Tap parent,
String path,
RecordReader recordReader)
throws IOException
- Specified by:
createTupleEntrySchemeIterator
in class BasePartitionTap<JobConf,RecordReader,OutputCollector>
- Throws:
IOException
getCurrentIdentifier
protected String getCurrentIdentifier(FlowProcess<JobConf> flowProcess)
- Specified by:
getCurrentIdentifier
in class BasePartitionTap<JobConf,RecordReader,OutputCollector>
sourceConfInit
public void sourceConfInit(FlowProcess<JobConf> flowProcess,
JobConf conf)
- Overrides:
sourceConfInit
in class Tap<JobConf,RecordReader,OutputCollector>
openForRead
public TupleEntryIterator openForRead(FlowProcess<JobConf> flowProcess,
RecordReader input)
throws IOException
- Overrides:
openForRead
in class BasePartitionTap<JobConf,RecordReader,OutputCollector>
- Throws:
IOException
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