RrdBackend (Javadocs [I2P+ 2.11.0+]

java.lang.Object
- org.rrd4j.core.RrdBackend

Direct Known Subclasses:

ByteBufferBackend, RrdRandomAccessFileBackend
```
public abstract class RrdBackend
extends Object
```
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 multiple backends out of the box. E.g.:
- RrdRandomAccessFileBackend: objects of this class are created from the RrdRandomAccessFileBackendFactory 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.

Field Summary

Fields
Modifier and Type Field and Description

protected static ByteOrder BYTEORDER
All ByteBuffer usage should use this standard order.

Fields
Modifier and Type	Field and Description
`protected static ByteOrder`	`BYTEORDER` All `ByteBuffer` usage should use this standard order.

Constructor Summary

Constructors
Modifier Constructor and Description

protected RrdBackend(String path)
Creates backend for a RRD storage with the given path.

Constructors
Modifier	Constructor and Description
`protected`	`RrdBackend(String path)` Creates backend for a RRD storage with the given path.

Method Summary

All Methods Static Methods Instance Methods Abstract Methods Concrete Methods
Modifier and Type	Method and Description
`protected abstract void`	`close()` Closes the underlying backend.
`(package private) void`	`done(RrdBackendFactory factory, PhantomReference<RrdDb> ref)`
`protected CharBuffer`	`getCharBuffer(long offset, int size)` Extract a CharBuffer from the backend, used by readString
`RrdBackendFactory`	`getFactory()`
`abstract long`	`getLength()` Returns the number of RRD bytes in the underlying storage.
`String`	`getPath()` Returns path to the storage.
`URI`	`getUri()` Return the URI associated to this backend, using the factory to generate it from the path.
`protected boolean`	`isCachingAllowed()` This method suggests the caching policy to the Rrd4j frontend (high-level) classes.
`(package private) static boolean`	`isInstanceCreated()` Checks if a backend instance has been created.
`protected abstract void`	`read(long offset, byte[] b)` Reads an array of bytes from the underlying storage starting from the given storage offset.
`byte[]`	`readAll()` Reads all RRD bytes from the underlying storage.
`protected double`	`readDouble(long offset)` Reads a double value from the underlying storage at the given offset.
`protected double[]`	`readDouble(long offset, int count)` Reads an array of double values from the underlying storage at the given offset.
`protected int`	`readInt(long offset)` Reads an integer value from the underlying storage at the given offset.
`protected long`	`readLong(long offset)` Reads a long value from the underlying storage at the given offset.
`protected short`	`readShort(long offset)` Reads a short value from the underlying storage at the given offset.
`protected String`	`readString(long offset)` Reads a string from the underlying storage at the given offset.
`protected void`	`rrdClose()` Closes the underlying backend.
`protected abstract void`	`setLength(long length)` Sets the number of bytes in the underlying RRD storage.
`protected abstract void`	`write(long offset, byte[] b)` Writes an array of bytes to the underlying storage starting from the given storage offset.
`protected void`	`writeDouble(long offset, double value)` Writes a double value to the underlying storage at the given offset.
`protected void`	`writeDouble(long offset, double[] values)` Writes an array of double values to the underlying storage at the given offset.
`protected void`	`writeDouble(long offset, double value, int count)` Writes multiple copies of a double value to the underlying storage at the given offset.
`protected void`	`writeInt(long offset, int value)` Writes an integer value to the underlying storage at the given offset.
`protected void`	`writeLong(long offset, long value)` Writes a long value to the underlying storage at the given offset.
`protected void`	`writeShort(long offset, short value)` Writes a short value to the underlying storage at the given offset.
`protected void`	`writeString(long offset, String value)` Writes a string to the underlying storage at the given offset.
`protected void`	`writeString(long offset, String value, int length)` Writes a string to the underlying storage at the given offset with a fixed length.

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - BYTEORDER
```
protected static final ByteOrder BYTEORDER
```
    All ByteBuffer usage should use this standard order.
- Constructor Detail
  - RrdBackend
```
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.
- Method Detail
  - close
```
protected abstract void close()
                       throws IOException
```
    Closes the underlying backend. Used internally, should not be called from external code.
    
    Throws:
    
    IOException - Thrown in case of I/O error
  - done
```
void done(RrdBackendFactory factory,
          PhantomReference<RrdDb> ref)
```
    Parameters:
    
    factory - the factory to set
  - getCharBuffer
```
protected CharBuffer getCharBuffer(long offset,
                                   int size)
                            throws IOException
```
    Extract a CharBuffer from the backend, used by readString
    
    Parameters:
    
    offset - the offset in the rrd
    
    size - the size of the buffer, in character
    
    Returns:
    
    a new CharBuffer
    
    Throws:
    
    IOException - if the read fails
  - getFactory
```
public RrdBackendFactory getFactory()
```
    Returns:
    
    the factory
  - getLength
```
public abstract long getLength()
                        throws IOException
```
    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.
  - getPath
```
public String getPath()
```
    Returns path to the storage.
    
    Returns:
    
    Storage path
  - getUri
```
public URI getUri()
```
    Return the URI associated to this backend, using the factory to generate it from the path.
    
    Returns:
    
    URI to this backend's rrd.
  - isCachingAllowed
```
protected boolean isCachingAllowed()
```
    This method suggests the caching policy to the Rrd4j frontend (high-level) classes. If true is returned, frontend 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 overridden in subclasses.
  - isInstanceCreated
```
static boolean isInstanceCreated()
```
    Checks if a backend instance has been created.
    
    Returns:
    
    true if a backend instance has been created, false otherwise.
  - read
```
protected abstract void read(long offset,
                             byte[] b)
                      throws IOException
```
    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
  - readAll
```
public final byte[] readAll()
                     throws IOException
```
    Reads all RRD bytes from the underlying storage.
    
    Returns:
    
    RRD bytes
    
    Throws:
    
    IOException - Thrown in case of I/O error
  - readDouble
```
protected double readDouble(long offset)
                     throws IOException
```
    Reads a double value from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    Returns:
    
    The double value read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - readDouble
```
protected double[] readDouble(long offset,
                              int count)
                       throws IOException
```
    Reads an array of double values from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    count - Number of double values to read.
    
    Returns:
    
    Array of double values read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - readInt
```
protected int readInt(long offset)
               throws IOException
```
    Reads an integer value from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    Returns:
    
    The integer value read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - readLong
```
protected long readLong(long offset)
                 throws IOException
```
    Reads a long value from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    Returns:
    
    The long value read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - readShort
```
protected short readShort(long offset)
                   throws IOException
```
    Reads a short value from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    Returns:
    
    The short value read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - readString
```
protected final String readString(long offset)
                           throws IOException
```
    Reads a string from the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    Returns:
    
    The string value read from storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - rrdClose
```
protected void rrdClose()
                 throws IOException
```
    Closes the underlying backend. Call by RrdDb#close() when it's closed. All subclass must keep calling it.
    
    Throws:
    
    IOException - Thrown in case of I/O error
  - setLength
```
protected abstract void setLength(long length)
                           throws IOException
```
    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.
  - write
```
protected abstract void write(long offset,
                              byte[] b)
                       throws IOException
```
    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
  - writeDouble
```
protected void writeDouble(long offset,
                           double value)
                    throws IOException
```
    Writes a double value to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - Double value to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeDouble
```
protected void writeDouble(long offset,
                           double[] values)
                    throws IOException
```
    Writes an array of double values to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    values - Array of double values to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeDouble
```
protected void writeDouble(long offset,
                           double value,
                           int count)
                    throws IOException
```
    Writes multiple copies of a double value to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - Double value to write.
    
    count - Number of times to write the value.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeInt
```
protected void writeInt(long offset,
                        int value)
                 throws IOException
```
    Writes an integer value to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - Integer value to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeLong
```
protected void writeLong(long offset,
                         long value)
                  throws IOException
```
    Writes a long value to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - Long value to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeShort
```
protected void writeShort(long offset,
                          short value)
                   throws IOException
```
    Writes a short value to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - Short value to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeString
```
protected final void writeString(long offset,
                                 String value)
                          throws IOException
```
    Writes a string to the underlying storage at the given offset.
    
    Parameters:
    
    offset - Storage offset.
    
    value - String value to write.
    
    Throws:
    
    IOException - Thrown in case of I/O error.
  - writeString
```
protected void writeString(long offset,
                           String value,
                           int length)
                    throws IOException
```
    Writes a string to the underlying storage at the given offset with a fixed length.
    
    Parameters:
    
    offset - Storage offset.
    
    value - String value to write.
    
    length - Fixed length for the string storage.
    
    Throws:
    
    IOException - Thrown in case of I/O error.

Class RrdBackend

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

BYTEORDER

Constructor Detail

RrdBackend

Method Detail

close

done

getCharBuffer

getFactory

getLength

getPath

getUri

isCachingAllowed

isInstanceCreated

read

readAll

readDouble

readDouble

readInt

readLong

readShort

readString

rrdClose

setLength

write

writeDouble

writeDouble

writeDouble

writeInt

writeLong

writeShort

writeString

writeString