com.google.appengine.tools.mapreduce

Class DatastoreMutationPool

java.lang.Object

com.google.appengine.tools.mapreduce.DatastoreMutationPool

public class DatastoreMutationPool
extends Object

DatastoreMutationPool allows you to pool datastore operations such that they are applied in batches, requiring fewer datastore API calls. Mutations are accumulated until they reach a count limit on the number of unflushed mutations, until they reach a size limit on the byte count of unflushed mutations, or until a manual flush is requested. A typical use would be:

   class Example extends Mapper<...> {
     ...
     private transient DatastoreMutationPool pool;
     ...

     public void beginSlice() {
       pool = DatastoreMutationPool.create();
     }

     public void endSlice() {
       pool.flush();
     }

     public void map(... value) {
       ...
       Entity entity = ...
       pool.put(entity);
       ...
     }
   }
 

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	DatastoreMutationPool.Params DatastoreMutationPool params.

Field Summary

Fields

Modifier and Type	Field and Description
static int	DEFAULT_BYTES_LIMIT
static int	DEFAULT_COUNT_LIMIT
static DatastoreMutationPool.Params	DEFAULT_PARAMS

Method Summary

Methods

Modifier and Type	Method and Description
static DatastoreMutationPool	create()
static DatastoreMutationPool	create(com.google.appengine.api.datastore.DatastoreService ds, DatastoreMutationPool.Params params)
void	delete(com.google.appengine.api.datastore.Key key) Adds a mutation to put the given entity to the datastore.
void	flush() Performs all pending mutations.
void	put(com.google.appengine.api.datastore.Entity entity) Adds a mutation deleting the entity with the given key.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_COUNT_LIMIT

public static final int DEFAULT_COUNT_LIMIT

See Also:

Constant Field Values

DEFAULT_BYTES_LIMIT

public static final int DEFAULT_BYTES_LIMIT

See Also:

Constant Field Values

DEFAULT_PARAMS

public static final DatastoreMutationPool.Params DEFAULT_PARAMS

Method Detail

create

public static DatastoreMutationPool create(com.google.appengine.api.datastore.DatastoreService ds,
                           DatastoreMutationPool.Params params)

create

public static DatastoreMutationPool create()

delete

public void delete(com.google.appengine.api.datastore.Key key)

Adds a mutation to put the given entity to the datastore.

put

public void put(com.google.appengine.api.datastore.Entity entity)

Adds a mutation deleting the entity with the given key.

flush

public void flush()

Performs all pending mutations.