public abstract class

RrdBackend

extends Object
java.lang.Object
   ↳ org.rrd4j.core.RrdBackend
Known Direct Subclasses
Known Indirect Subclasses

Class Overview

Base implementation class for all backend classes. Each Round Robin Database object (RrdDb object) is backed with a single RrdBackend object which performs actual I/O operations on the underlying storage. Rrd4j supports three different bakcends out of the box:

  • RrdFileBackend: objects of this class are created from the RrdFileBackendFactory class. This was the default backend used in all Rrd4j releases prior to 1.4.0. It uses java.io.* package and RandomAccessFile class to store RRD data in files on the disk.
  • RrdNioBackend: objects of this class are created from the RrdNioBackendFactory class. The backend uses java.io.* and java.nio.* classes (mapped ByteBuffer) to store RRD data in files on the disk. This backend is fast, very fast, but consumes a lot of memory (borrowed not from the JVM but from the underlying operating system directly). This is the default backend used in Rrd4j since 1.4.0 release.
  • RrdMemoryBackend: objects of this class are created from the RrdMemoryBackendFactory class. This backend stores all data in memory. Once JVM exits, all data gets lost. The backend is extremely fast and memory hungry.
To create your own backend in order to provide some custom type of RRD storage, you should do the following:

  • Create your custom RrdBackend class (RrdCustomBackend, for example) by extending RrdBackend class. You have to implement all abstract methods defined in the base class.
  • Create your custom RrdBackendFactory class (RrdCustomBackendFactory, for example) by extending RrdBackendFactory class. You have to implement all abstract methods defined in the base class. Your custom factory class will actually create custom backend objects when necessary.
  • Create instance of your custom RrdBackendFactory and register it as a regular factory available to Rrd4j framework. See javadoc for RrdBackendFactory to find out how to do this

Summary

Protected Constructors
RrdBackend(String path)
Creates backend for a RRD storage with the given path.
Public Methods
void close()
Closes the underlying backend.
abstract long getLength()
Returns the number of RRD bytes in the underlying storage.
String getPath()
Returns path to the storage.
final byte[] readAll()
Reads all RRD bytes from the underlying storage
Protected Methods
boolean isCachingAllowed()
This method suggests the caching policy to the Rrd4j frontend (high-level) classes.
abstract void read(long offset, byte[] b)
Reads an array of bytes from the underlying storage starting from the given storage offset.
abstract void setLength(long length)
Sets the number of bytes in the underlying RRD storage.
abstract void write(long offset, byte[] b)
Writes an array of bytes to the underlying storage starting from the given storage offset.
[Expand]
Inherited Methods
From class java.lang.Object

Protected Constructors

protected RrdBackend (String path)

Creates backend for a RRD storage with the given path.

Parameters
path String identifying RRD storage. For files on the disk, this argument should represent file path. Other storage types might interpret this argument differently.

Public Methods

public void close ()

Closes the underlying backend.

Throws
IOException Thrown in case of I/O error

public abstract long getLength ()

Returns the number of RRD bytes in the underlying storage.

Returns
  • Number of RRD bytes in the storage.
Throws
IOException Thrown in case of I/O error.

public String getPath ()

Returns path to the storage.

Returns
  • Storage path

public final byte[] readAll ()

Reads all RRD bytes from the underlying storage

Returns
  • RRD bytes
Throws
IOException Thrown in case of I/O error

Protected Methods

protected boolean isCachingAllowed ()

This method suggests the caching policy to the Rrd4j frontend (high-level) classes. If true is returned, frontent classes will cache frequently used parts of a RRD file in memory to improve performance. If false is returned, high level classes will never cache RRD file sections in memory.

Returns
  • true if file caching is enabled, false otherwise. By default, the method returns true but it can be overriden in subclasses.

protected abstract void read (long offset, byte[] b)

Reads an array of bytes from the underlying storage starting from the given storage offset.

Parameters
offset Storage offset.
b Array which receives bytes from the underlying storage
Throws
IOException Thrown in case of I/O error

protected abstract void setLength (long length)

Sets the number of bytes in the underlying RRD storage. This method is called only once, immediately after a new RRD storage gets created.

Parameters
length Length of the underlying RRD storage in bytes.
Throws
IOException Thrown in case of I/O error.

protected abstract void write (long offset, byte[] b)

Writes an array of bytes to the underlying storage starting from the given storage offset.

Parameters
offset Storage offset.
b Array of bytes that should be copied to the underlying storage
Throws
IOException Thrown in case of I/O error