com.db4o.io

Class NonFlushingIoAdapter

java.lang.Object

com.db4o.io.IoAdapter

com.db4o.io.VanillaIoAdapter

com.db4o.io.NonFlushingIoAdapter

Deprecated.

use Storage-equivalent instead.

public class NonFlushingIoAdapter
extends VanillaIoAdapter

Delegating IoAdapter that does not pass on calls to sync data to the underlying device.

This IoAdapter can be used to improve performance at the cost of a higher risk of database file corruption upon abnormal termination of a session against a database.

An example of possible usage:
RandomAccessFileAdapter randomAccessFileAdapter = new RandomAccessFileAdapter();
NonFlushingIoAdapter nonFlushingIoAdapter = new NonFlushingIoAdapter(randomAccessFileAdapter);
CachedIoAdapter cachedIoAdapter = new CachedIoAdapter(nonFlushingIoAdapter);
Configuration configuration = Db4o.newConfiguration();
configuration.io(cachedIoAdapter);


db4o uses a resume-commit-on-crash strategy to ensure ACID transactions. When a transaction commits,
- (1) a list "pointers that are to be modified" is written to the database file,
- (2) the database file is switched into "in-commit" mode,
- (3) the pointers are actually modified in the database file,
- (4) the database file is switched to "not-in-commit" mode.
If the system is halted by a hardware or power failure
- before (2)
all objects will be available as before the commit
- between (2) and (4) the commit is restarted when the database file is opened the next time, all pointers will be read from the "pointers to be modified" list and all of them will be modified to the state they are intended to have after commit
- after (4) no work is necessary, the transaction is committed.

In order for the above to be 100% failsafe, the order of writes to the storage medium has to be obeyed. On operating systems that use in-memory file caching, the OS cache may revert the order of writes to optimize file performance.

db4o enforces the correct write order by calling sync() after every single one of the above steps during transaction commit. The calls to sync() have a high performance cost. By using this IoAdapter it is possible to omit these calls, at the cost of a risc of corrupted database files upon hardware-, power- or operating system failures.

Field Summary

Fields inherited from class com.db4o.io.VanillaIoAdapter

_delegate

Constructor Summary

Constructors

Constructor and Description
NonFlushingIoAdapter(IoAdapter delegateAdapter) Deprecated.

Method Summary

Methods

Modifier and Type	Method and Description
IoAdapter	open(java.lang.String path, boolean lockFile, long initialLength, boolean readOnly) Deprecated.
void	sync() Deprecated.

Methods inherited from class com.db4o.io.VanillaIoAdapter

close, delete, exists, getLength, read, seek, write

Methods inherited from class com.db4o.io.IoAdapter

blockCopy, blockSeek, blockSeek, blockSize, blockSize, copy, delegatedIoAdapter, read, regularAddress, write

Methods inherited from class java.lang.Object

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

Constructor Detail

NonFlushingIoAdapter

public NonFlushingIoAdapter(IoAdapter delegateAdapter)

Deprecated.

Method Detail

open

public IoAdapter open(java.lang.String path,
             boolean lockFile,
             long initialLength,
             boolean readOnly)
               throws Db4oIOException

Deprecated.

Specified by:

open in class IoAdapter

Throws:

Db4oIOException

sync

public void sync()
          throws Db4oIOException

Deprecated.

Overrides:

sync in class VanillaIoAdapter

Throws:

Db4oIOException