org.apache.pig
Class StoreFunc

java.lang.Object
  extended by org.apache.pig.StoreFunc
All Implemented Interfaces:
StoreFuncInterface
Direct Known Subclasses:
DBStorage, JsonStorage, MultiStorage, TableStorer

@InterfaceAudience.Public
@InterfaceStability.Stable
public abstract class StoreFunc
extends Object
implements StoreFuncInterface

StoreFuncs take records from Pig's processing and store them into a data store. Most frequently this is an HDFS file, but it could also be an HBase instance, RDBMS, etc.


Constructor Summary
StoreFunc()
           
 
Method Summary
 void checkSchema(ResourceSchema s)
          Set the schema for data to be stored.
 void cleanupOnFailure(String location, org.apache.hadoop.mapreduce.Job job)
          This method will be called by Pig if the job which contains this store fails.
static void cleanupOnFailureImpl(String location, org.apache.hadoop.mapreduce.Job job)
          Implementation for cleanupOnFailure(String, Job).
abstract  org.apache.hadoop.mapreduce.OutputFormat getOutputFormat()
          Return the OutputFormat associated with StoreFunc.
abstract  void prepareToWrite(org.apache.hadoop.mapreduce.RecordWriter writer)
          Initialize StoreFunc to write data.
abstract  void putNext(Tuple t)
          Write a tuple to the data store.
 String relToAbsPathForStoreLocation(String location, org.apache.hadoop.fs.Path curDir)
          This method is called by the Pig runtime in the front end to convert the output location to an absolute path if the location is relative.
 void setStoreFuncUDFContextSignature(String signature)
          This method will be called by Pig both in the front end and back end to pass a unique signature to the StoreFunc which it can use to store information in the UDFContext which it needs to store between various method invocations in the front end and back end.
abstract  void setStoreLocation(String location, org.apache.hadoop.mapreduce.Job job)
          Communicate to the storer the location where the data needs to be stored.
 void warn(String msg, Enum warningEnum)
          Issue a warning.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

StoreFunc

public StoreFunc()
Method Detail

relToAbsPathForStoreLocation

public String relToAbsPathForStoreLocation(String location,
                                           org.apache.hadoop.fs.Path curDir)
                                    throws IOException
This method is called by the Pig runtime in the front end to convert the output location to an absolute path if the location is relative. The StoreFunc implementation is free to choose how it converts a relative location to an absolute location since this may depend on what the location string represent (hdfs path or some other data source).

Specified by:
relToAbsPathForStoreLocation in interface StoreFuncInterface
Parameters:
location - location as provided in the "store" statement of the script
curDir - the current working direction based on any "cd" statements in the script before the "store" statement. If there are no "cd" statements in the script, this would be the home directory -
/user/ 
Returns:
the absolute location based on the arguments passed
Throws:
IOException - if the conversion is not possible

getOutputFormat

public abstract org.apache.hadoop.mapreduce.OutputFormat getOutputFormat()
                                                                  throws IOException
Return the OutputFormat associated with StoreFunc. This will be called on the front end during planning and on the backend during execution.

Specified by:
getOutputFormat in interface StoreFuncInterface
Returns:
the OutputFormat associated with StoreFunc
Throws:
IOException - if an exception occurs while constructing the OutputFormat

setStoreLocation

public abstract void setStoreLocation(String location,
                                      org.apache.hadoop.mapreduce.Job job)
                               throws IOException
Communicate to the storer the location where the data needs to be stored. The location string passed to the StoreFunc here is the return value of relToAbsPathForStoreLocation(String, Path) This method will be called in the frontend and backend multiple times. Implementations should bear in mind that this method is called multiple times and should ensure there are no inconsistent side effects due to the multiple calls. checkSchema(ResourceSchema) will be called before any call to setStoreLocation(String, Job).

Specified by:
setStoreLocation in interface StoreFuncInterface
Parameters:
location - Location returned by relToAbsPathForStoreLocation(String, Path)
job - The Job object
Throws:
IOException - if the location is not valid.

checkSchema

public void checkSchema(ResourceSchema s)
                 throws IOException
Set the schema for data to be stored. This will be called on the front end during planning if the store is associated with a schema. A Store function should implement this function to check that a given schema is acceptable to it. For example, it can check that the correct partition keys are included; a storage function to be written directly to an OutputFormat can make sure the schema will translate in a well defined way. Default implementation is a no-op.

Specified by:
checkSchema in interface StoreFuncInterface
Parameters:
s - to be checked
Throws:
IOException - if this schema is not acceptable. It should include a detailed error message indicating what is wrong with the schema.

prepareToWrite

public abstract void prepareToWrite(org.apache.hadoop.mapreduce.RecordWriter writer)
                             throws IOException
Initialize StoreFunc to write data. This will be called during execution on the backend before the call to putNext.

Specified by:
prepareToWrite in interface StoreFuncInterface
Parameters:
writer - RecordWriter to use.
Throws:
IOException - if an exception occurs during initialization

putNext

public abstract void putNext(Tuple t)
                      throws IOException
Write a tuple to the data store.

Specified by:
putNext in interface StoreFuncInterface
Parameters:
t - the tuple to store.
Throws:
IOException - if an exception occurs during the write

setStoreFuncUDFContextSignature

public void setStoreFuncUDFContextSignature(String signature)
This method will be called by Pig both in the front end and back end to pass a unique signature to the StoreFunc which it can use to store information in the UDFContext which it needs to store between various method invocations in the front end and back end. This method will be called before other methods in StoreFunc. This is necessary because in a Pig Latin script with multiple stores, the different instances of store functions need to be able to find their (and only their) data in the UDFContext object. The default implementation is a no-op.

Specified by:
setStoreFuncUDFContextSignature in interface StoreFuncInterface
Parameters:
signature - a unique signature to identify this StoreFunc

cleanupOnFailure

public void cleanupOnFailure(String location,
                             org.apache.hadoop.mapreduce.Job job)
                      throws IOException
This method will be called by Pig if the job which contains this store fails. Implementations can clean up output locations in this method to ensure that no incorrect/incomplete results are left in the output location. The default implementation deletes the output location if it is a FileSystem location.

Specified by:
cleanupOnFailure in interface StoreFuncInterface
Parameters:
location - Location returned by relToAbsPathForStoreLocation(String, Path)
job - The Job object - this should be used only to obtain cluster properties through JobContext.getConfiguration() and not to set/query any runtime job information.
Throws:
IOException

cleanupOnFailureImpl

public static void cleanupOnFailureImpl(String location,
                                        org.apache.hadoop.mapreduce.Job job)
                                 throws IOException
Implementation for cleanupOnFailure(String, Job). This removes a file from HDFS.

Parameters:
location - file name (or URI) of file to remove
job - Hadoop job, used to access the appropriate file system.
Throws:
IOException

warn

public final void warn(String msg,
                       Enum warningEnum)
Issue a warning. Warning messages are aggregated and reported to the user.

Parameters:
msg - String message of the warning
warningEnum - type of warning


Copyright © 2007-2012 The Apache Software Foundation