java.lang.Object
- org.apache.activemq.store.kahadb.disk.page.PageFile

```
public class PageFile
extends Object
```
A PageFile provides you random access to fixed sized disk pages. This object is not thread safe and therefore access to it should be externally synchronized.
The file has 3 parts: Metadata Space: 4k : Reserved metadata area. Used to store persistent config about the file. Recovery Buffer Space: Page Size * 1000 : This is a redo log used to prevent partial page writes from making the file inconsistent Page Space: The pages in the page file.

Nested Class Summary

Nested Classes
Modifier and Type Class Description

static class PageFile.MetaData
The MetaData object hold the persistent data associated with a PageFile object.

Field Summary

Fields
Modifier and Type Field Description

static int DEFAULT_PAGE_CACHE_SIZE

static int DEFAULT_PAGE_SIZE

static int DEFAULT_WRITE_BATCH_SIZE

Constructor Summary

Constructors
Constructor Description

PageFile(File directory, String name)
Creates a PageFile in the specified directory who's data files are named by name.

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method	Description
`void`	`allowIOResumption()`
`void`	`archive()`
`void`	`delete()`	Deletes the files used by the PageFile object.
`void`	`flush()`	Flush and sync all write buffers to disk.
`void`	`freePage(long pageId)`
`File`	`getDirectory()`
`long`	`getDiskSize()`
`File`	`getFile()`
`File`	`getFreeFile()`
`long`	`getFreePageCount()`
`float`	`getLFUEvictionFactor()`
`int`	`getPageCacheSize()`
`int`	`getPageContentSize()`
`long`	`getPageCount()`
`int`	`getPageSize()`
`File`	`getRecoveryFile()`
`int`	`getRecoveryFileMaxPageCount()`
`int`	`getRecoveryFileMinPageCount()`
`int`	`getWriteBatchSize()`
`boolean`	`isCleanShutdown()`
`boolean`	`isEnableDiskSyncs()`
`boolean`	`isEnabledWriteThread()`
`boolean`	`isEnablePageCaching()`
`boolean`	`isEnableRecoveryFile()`	Is the recovery buffer used to double buffer page writes.
`boolean`	`isFreePage(long pageId)`
`boolean`	`isLoaded()`
`boolean`	`isUseLFRUEviction()`
`void`	`load()`	Loads the page file so that it can be accessed for read/write purposes.
`void`	`removeTmpFile(File file, RandomAccessFile randomAccessFile)`
`void`	`setEnableDiskSyncs(boolean syncWrites)`	Allows you enable syncing writes to disk.
`void`	`setEnablePageCaching(boolean enablePageCaching)`
`void`	`setEnableRecoveryFile(boolean doubleBuffer)`	Sets if the recovery buffer uses to double buffer page writes.
`void`	`setEnableWriteThread(boolean enableAsyncWrites)`
`void`	`setLFUEvictionFactor(float LFUEvictionFactor)`
`void`	`setPageCacheSize(int pageCacheSize)`
`void`	`setPageSize(int pageSize)`	Configures the page size used by the page file.
`void`	`setRecoveryFileMaxPageCount(int recoveryFileMaxPageCount)`
`void`	`setRecoveryFileMinPageCount(int recoveryFileMinPageCount)`
`void`	`setUseLFRUEviction(boolean useLFRUEviction)`
`void`	`setWriteBatchSize(int writeBatchSize)`
`long`	`toOffset(long pageId)`
`String`	`toString()`
`Transaction`	`tx()`
`void`	`unload()`	Unloads a previously loaded PageFile.

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

- Field Detail
  - DEFAULT_PAGE_SIZE
```
public static final int DEFAULT_PAGE_SIZE
```
  - DEFAULT_WRITE_BATCH_SIZE
```
public static final int DEFAULT_WRITE_BATCH_SIZE
```
  - DEFAULT_PAGE_CACHE_SIZE
```
public static final int DEFAULT_PAGE_CACHE_SIZE
```
- Constructor Detail
  - PageFile
```
public PageFile(File directory,
                String name)
```
    Creates a PageFile in the specified directory who's data files are named by name.
- Method Detail
  - tx
```
public Transaction tx()
```
  - delete
```
public void delete()
            throws IOException
```
    Deletes the files used by the PageFile object. This method can only be used when this object is not loaded.
    
    Throws:
    
    IOException - if the files cannot be deleted.
    
    IllegalStateException - if this PageFile is loaded
  - archive
```
public void archive()
             throws IOException
```
    Throws:
    
    IOException
  - load
```
public void load()
          throws IOException,
                 IllegalStateException
```
    Loads the page file so that it can be accessed for read/write purposes. This allocates OS resources. If this is the first time the page file is loaded, then this creates the page file in the file system.
    
    Throws:
    
    IOException - If the page file cannot be loaded. This could be cause the existing page file is corrupt is a bad version or if there was a disk error.
    
    IllegalStateException - If the page file was already loaded.
  - unload
```
public void unload()
            throws IOException
```
    Unloads a previously loaded PageFile. This deallocates OS related resources like file handles. once unloaded, you can no longer use the page file to read or write Pages.
    
    Throws:
    
    IOException - if there was a disk error occurred while closing the down the page file.
    
    IllegalStateException - if the PageFile is not loaded
  - isLoaded
```
public boolean isLoaded()
```
  - isCleanShutdown
```
public boolean isCleanShutdown()
```
  - allowIOResumption
```
public void allowIOResumption()
```
  - flush
```
public void flush()
           throws IOException
```
    Flush and sync all write buffers to disk.
    
    Throws:
    
    IOException - If an disk error occurred.
  - toString
```
public String toString()
```
    Overrides:
    
    toString in class Object
  - getFreeFile
```
public File getFreeFile()
```
  - getRecoveryFile
```
public File getRecoveryFile()
```
  - toOffset
```
public long toOffset(long pageId)
```
  - isEnableRecoveryFile
```
public boolean isEnableRecoveryFile()
```
    Is the recovery buffer used to double buffer page writes. Enabled by default.
    
    Returns:
    
    is the recovery buffer enabled.
  - setEnableRecoveryFile
```
public void setEnableRecoveryFile(boolean doubleBuffer)
```
    Sets if the recovery buffer uses to double buffer page writes. Enabled by default. Disabling this may potentially cause partial page writes which can lead to page file corruption.
  - isEnableDiskSyncs
```
public boolean isEnableDiskSyncs()
```
    Returns:
    
    Are page writes synced to disk?
  - setEnableDiskSyncs
```
public void setEnableDiskSyncs(boolean syncWrites)
```
    Allows you enable syncing writes to disk.
  - getPageSize
```
public int getPageSize()
```
    Returns:
    
    the page size
  - getPageContentSize
```
public int getPageContentSize()
```
    Returns:
    
    the amount of content data that a page can hold.
  - setPageSize
```
public void setPageSize(int pageSize)
                 throws IllegalStateException
```
    Configures the page size used by the page file. By default it is 4k. Once a page file is created on disk, subsequent loads of that file will use the original pageSize. Once the PageFile is loaded, this setting can no longer be changed.
    
    Parameters:
    
    pageSize - the pageSize to set
    
    Throws:
    
    IllegalStateException - once the page file is loaded.
  - isEnablePageCaching
```
public boolean isEnablePageCaching()
```
    Returns:
    
    true if read page caching is enabled
  - setEnablePageCaching
```
public void setEnablePageCaching(boolean enablePageCaching)
```
    Parameters:
    
    enablePageCaching - allows you to enable read page caching
  - getPageCacheSize
```
public int getPageCacheSize()
```
    Returns:
    
    the maximum number of pages that will get stored in the read page cache.
  - setPageCacheSize
```
public void setPageCacheSize(int pageCacheSize)
```
    Parameters:
    
    pageCacheSize - Sets the maximum number of pages that will get stored in the read page cache.
  - isEnabledWriteThread
```
public boolean isEnabledWriteThread()
```
  - setEnableWriteThread
```
public void setEnableWriteThread(boolean enableAsyncWrites)
```
  - getDiskSize
```
public long getDiskSize()
                 throws IOException
```
    Throws:
    
    IOException
  - isFreePage
```
public boolean isFreePage(long pageId)
```
  - getPageCount
```
public long getPageCount()
```
    Returns:
    
    the number of pages allocated in the PageFile
  - getRecoveryFileMinPageCount
```
public int getRecoveryFileMinPageCount()
```
  - getFreePageCount
```
public long getFreePageCount()
```
  - setRecoveryFileMinPageCount
```
public void setRecoveryFileMinPageCount(int recoveryFileMinPageCount)
```
  - getRecoveryFileMaxPageCount
```
public int getRecoveryFileMaxPageCount()
```
  - setRecoveryFileMaxPageCount
```
public void setRecoveryFileMaxPageCount(int recoveryFileMaxPageCount)
```
  - getWriteBatchSize
```
public int getWriteBatchSize()
```
  - setWriteBatchSize
```
public void setWriteBatchSize(int writeBatchSize)
```
  - getLFUEvictionFactor
```
public float getLFUEvictionFactor()
```
  - setLFUEvictionFactor
```
public void setLFUEvictionFactor(float LFUEvictionFactor)
```
  - isUseLFRUEviction
```
public boolean isUseLFRUEviction()
```
  - setUseLFRUEviction
```
public void setUseLFRUEviction(boolean useLFRUEviction)
```
  - freePage
```
public void freePage(long pageId)
```
  - removeTmpFile
```
public void removeTmpFile(File file,
                          RandomAccessFile randomAccessFile)
                   throws IOException
```
    Throws:
    
    IOException
  - getFile
```
public File getFile()
```
  - getDirectory
```
public File getDirectory()
```

Modifier and Type	Field	Description
`static int`	`DEFAULT_PAGE_CACHE_SIZE`
`static int`	`DEFAULT_PAGE_SIZE`
`static int`	`DEFAULT_WRITE_BATCH_SIZE`

Class PageFile

Nested Class Summary

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

DEFAULT_PAGE_SIZE

DEFAULT_WRITE_BATCH_SIZE

DEFAULT_PAGE_CACHE_SIZE

Constructor Detail

PageFile

Method Detail

tx

delete

archive

load

unload

isLoaded

isCleanShutdown

allowIOResumption

flush

toString

getFreeFile

getRecoveryFile

toOffset

isEnableRecoveryFile

setEnableRecoveryFile

isEnableDiskSyncs

setEnableDiskSyncs

getPageSize

getPageContentSize

setPageSize

isEnablePageCaching

setEnablePageCaching

getPageCacheSize

setPageCacheSize

isEnabledWriteThread

setEnableWriteThread

getDiskSize

isFreePage

getPageCount

getRecoveryFileMinPageCount

getFreePageCount

setRecoveryFileMinPageCount

getRecoveryFileMaxPageCount

setRecoveryFileMaxPageCount

getWriteBatchSize

setWriteBatchSize

getLFUEvictionFactor

setLFUEvictionFactor

isUseLFRUEviction

setUseLFRUEviction

freePage

removeTmpFile

getFile

getDirectory