org.apache.pig
Interface StoreFuncInterface

All Known Implementing Classes:
AvroStorage, BinStorage, CSVExcelStorage, DBStorage, HBaseStorage, IndexedStorage, InterStorage, JsonStorage, MultiStorage, PigStorage, PigStorageSchema, StoreFunc, TableStorer, TFileStorage

@InterfaceAudience.Public
@InterfaceStability.Stable
public interface 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.


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.
 org.apache.hadoop.mapreduce.OutputFormat getOutputFormat()
          Return the OutputFormat associated with StoreFuncInterface.
 void prepareToWrite(org.apache.hadoop.mapreduce.RecordWriter writer)
          Initialize StoreFuncInterface to write data.
 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 StoreFuncInterface 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.
 void setStoreLocation(String location, org.apache.hadoop.mapreduce.Job job)
          Communicate to the storer the location where the data needs to be stored.
 

Method Detail

relToAbsPathForStoreLocation

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 StoreFuncInterface 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). The static method LoadFunc.getAbsolutePath(java.lang.String, org.apache.hadoop.fs.Path) provides a default implementation for hdfs and hadoop local file system and it can be used to implement this method.

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

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

Returns:
the OutputFormat associated with StoreFuncInterface
Throws:
IOException - if an exception occurs while constructing the OutputFormat

setStoreLocation

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 StoreFuncInterface 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).

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

checkSchema

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.

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

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

Parameters:
writer - RecordWriter to use.
Throws:
IOException - if an exception occurs during initialization

putNext

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

Parameters:
t - the tuple to store.
Throws:
IOException - if an exception occurs during the write

setStoreFuncUDFContextSignature

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 StoreFuncInterface 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 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.

Parameters:
signature - a unique signature to identify this StoreFuncInterface

cleanupOnFailure

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

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


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