fabric.store.db

Class MemoryDB

java.lang.Object

fabric.store.db.ObjectDB

fabric.store.db.MemoryDB

public class MemoryDB
extends ObjectDB

An in-memory implementation of the ObjectDB. This class assumes there will be no failures and hopefully will provide very high performance at the cost of no fault tolerance whatsoever. This class has a simple facility for loading and saving the database to a file. During the save process, no workers should be actively preparing or committing transactions, and all prepared transactions should have been either committed or aborted.

Nested Class Summary

Nested classes/interfaces inherited from class fabric.store.db.ObjectDB

ObjectDB.PendingTransaction, ObjectDB.UpdateMode

Field Summary

Fields inherited from class fabric.store.db.ObjectDB

name, pendingByTid, rwLocks

Constructor Summary

Constructors

Constructor and Description
MemoryDB(java.lang.String name, java.security.PrivateKey privateKey) Opens the store contained in file "var/storeName" if it exists, or an empty store otherwise.

Method Summary

Modifier and Type	Method and Description
void	close() Gracefully shuts down the object database.
void	commit(long tid, RemoteIdentity<RemoteWorker> workerIdentity, SubscriptionManager sm) Causes the objects prepared in transaction [tid] to be committed.
boolean	exists(long onum) Checks whether an object with the corresponding onum exists, in either prepared or committed form.
void	finishPrepare(long tid, Principal worker) Notifies the database that the given transaction is finished preparing.
protected boolean	isInitialized() Determines whether the object database has been initialized.
long[]	newOnums(int num) Returns a set of onums that aren't currently occupied.
SerializedObject	read(long onum) Returns the object stored at a particular onum.
void	rollback(long tid, Principal worker) Causes the objects prepared in transaction [tid] to be discarded.
protected void	setInitialized() Sets a flag to indicate that the object database has been initialized.

Methods inherited from class fabric.store.db.ObjectDB

abortPrepare, beginTransaction, ensureInit, getName, getVersion, isPrepared, isWritten, notifyCommittedUpdate, prepareRead, prepareUpdate, readGroup, unpin

Methods inherited from class java.lang.Object

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

Constructor Detail

MemoryDB

public MemoryDB(java.lang.String name,
                java.security.PrivateKey privateKey)

Opens the store contained in file "var/storeName" if it exists, or an empty store otherwise.

Parameters:

name - name of store to create database for.

Method Detail

finishPrepare

public void finishPrepare(long tid,
                          Principal worker)

Description copied from class: ObjectDB

Notifies the database that the given transaction is finished preparing. The transaction is not considered to be prepared until this is called. After calling this method, there should not be any further calls to registerRead() or registerUpdate() for the given transaction. This method MUST be called before calling commit().

Upon receiving this call, the object database should save the prepared transaction to stable storage so that it can be recovered in case of failure.

Specified by:

finishPrepare in class ObjectDB

commit

public void commit(long tid,
                   RemoteIdentity<RemoteWorker> workerIdentity,
                   SubscriptionManager sm)
            throws AccessException

Description copied from class: ObjectDB

Causes the objects prepared in transaction [tid] to be committed. The changes will hereafter be visible to read.

Specified by:

commit in class ObjectDB

Parameters:

tid - the transaction id

workerIdentity - the remote worker that is performing the commit

Throws:

AccessException - if the principal differs from the caller of prepare()

rollback

public void rollback(long tid,
                     Principal worker)
              throws AccessException

Description copied from class: ObjectDB

Causes the objects prepared in transaction [tid] to be discarded.

Specified by:

rollback in class ObjectDB

Parameters:

tid - the transaction id

worker - the principal requesting the rollback

Throws:

AccessException - if the principal differs from the caller of prepare()

read

public SerializedObject read(long onum)

Description copied from class: ObjectDB

Returns the object stored at a particular onum.

Specified by:

read in class ObjectDB

Parameters:

onum - the identifier

Returns:

the object or null if no object exists at the given onum

exists

public boolean exists(long onum)

Description copied from class: ObjectDB

Checks whether an object with the corresponding onum exists, in either prepared or committed form.

Specified by:

exists in class ObjectDB

Parameters:

onum - the onum of to check

Returns:

true if an object exists for onum

newOnums

public long[] newOnums(int num)

Description copied from class: ObjectDB

Returns a set of onums that aren't currently occupied. The ObjectDB may return the same onum more than once from this method, althogh doing so would encourage collisions. There is no assumption of unpredictability or randomness about the returned ids.

The returned onums should be packed in the lower 48 bits. We assume that the object database is never full, and can always provide new onums

Specified by:

newOnums in class ObjectDB

Parameters:

num - the number of onums to return

Returns:

num fresh onums

close

public void close()
           throws java.io.IOException

Description copied from class: ObjectDB

Gracefully shuts down the object database.

Specified by:

close in class ObjectDB

Throws:

java.io.IOException

isInitialized

protected boolean isInitialized()

Description copied from class: ObjectDB

Determines whether the object database has been initialized.

Specified by:

isInitialized in class ObjectDB

setInitialized

protected void setInitialized()

Description copied from class: ObjectDB

Sets a flag to indicate that the object database has been initialized.

Specified by:

setInitialized in class ObjectDB