org.netbeans.mdr.persistence.btreeimpl.btreestorage

Class FileCache

java.lang.Object

org.netbeans.mdr.persistence.btreeimpl.btreestorage.FileCache

public class FileCache
extends java.lang.Object

FileCache provides transactional cached access to a set of files. Changes to these files are accumulated both in memory and on disk until a commit is requested, at which time they are flushed to disk. If the program exits for any reason without comitting, any changes which were written to disk are rolled back to the last commit point the next time the FileCache is opened.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	FileCache.NotifyOnCommit An object which needs to be notified before the cache commits (for instance, to write any changes to the cache before the cache is flushed to disk) implements this interface, and calls addNotifier on the cache.

Constructor Summary

Constructors

Constructor and Description
FileCache(int pgSize, int numBufs, java.lang.String[] names, java.lang.String logName) Create the cache and open the files.

Method Summary

Methods

Modifier and Type	Method and Description
void	abort() close all files without comitting
void	addNotifier(FileCache.NotifyOnCommit notified) Add to the list of objects to be notified before commit
void	close() commit all changes and close all cached files
void	commit() commit all changes
void	dumpCache(java.io.PrintStream strm) for debugging
CachedPage	getPage(int fileidx, int pageNum) Get the single page at the desired offset into the file This implicitly pins that pages.
CachedPage[]	getPages(int fileidx, int first, int size) Get the pages which contain the desired bytes from the file This implicitly pins these pages.
void	setWritable(CachedPage page) Make the specified page writable.
void	setWritable(CachedPage[] pages) Make the specified pages writable.
void	showStats(java.io.PrintStream strm) Show caching statistics
void	showStats(java.io.PrintWriter strm) Show caching statistics
void	unpin(CachedPage page) unpin a page.
void	unpin(CachedPage[] pages) unpin a set of pages.

Methods inherited from class java.lang.Object

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

Constructor Detail

FileCache

public FileCache(int pgSize,
         int numBufs,
         java.lang.String[] names,
         java.lang.String logName)
          throws StorageException

Create the cache and open the files. The files are assumed already to exist and have valid, identical file headers.

Parameters:

pgSize - the cache's page size

numBufs - the number of page buffers to create

names - the files to access via the cache

logName - the name of the log file

Throws:

StorageException - I/O error opening or reading the files

BadParameterException - if the file do not have identical file headers, or the log file exists but is not consistent with the files

ConsistencyException - if the log file exists and is corrupted

Method Detail

abort

public void abort()
           throws StorageException

close all files without comitting

Throws:

StorageException - I/O error closing the files

close

public void close()
           throws StorageException

commit all changes and close all cached files

Throws:

StorageException - I/O error closing the files

commit

public void commit()
            throws StorageException

commit all changes

Throws:

StorageException - I/O error writing the files

unpin

public void unpin(CachedPage[] pages)
           throws StorageException

unpin a set of pages. Until unpinned the same number of times that they have been pinned, pages cannot be released from the cache.

Parameters:

pages - the pages to unpin

Throws:

BadParameterException - if the page is not pinned

StorageException

unpin

public void unpin(CachedPage page)
           throws StorageException

unpin a page. Until unpinned the same number of times it has been pinned, a page cannot be released from the cache.

Parameters:

page - the page to unpin

Throws:

BadParameterException - if any of the pages are not pinned

StorageException

getPages

public CachedPage[] getPages(int fileidx,
                    int first,
                    int size)
                      throws StorageException

Get the pages which contain the desired bytes from the file This implicitly pins these pages. Note that these pages may extend past the current EOF; that is, this routine may extend the file.

Parameters:

fileidx - the index of the file containing the page.

first - the number of the first page to get

length - the number of pages to get

Returns:

the array of pages requested.

Throws:

StorageException - I/O error reading the pages

getPage

public CachedPage getPage(int fileidx,
                 int pageNum)
                   throws StorageException

Get the single page at the desired offset into the file This implicitly pins that pages. Note that this may may exist past the current EOF; that is, this routine may extend the file.

Parameters:

fileidx - the index of the file containing the page.

pageNum - the page number to get

Returns:

the page requested

Throws:

StorageException - I/O error reading the page

setWritable

public void setWritable(CachedPage page)
                 throws StorageException

Make the specified page writable. If it was not writable previously, this causes it to be logged. This must be called before the page is modified. If the cache is not currently in a transaction, this implicitly begins one.

Parameters:

page - The page to be made writable.

Throws:

StorageException - I/O error logging the page

setWritable

public void setWritable(CachedPage[] pages)
                 throws StorageException

Make the specified pages writable. If any were not writable previously, this causes them to be logged. This be called before the pages are modified.

Parameters:

pages - The pages to be made writable.

Throws:

StorageException - I/O error logging the pages

dumpCache

public void dumpCache(java.io.PrintStream strm)

for debugging

showStats

public void showStats(java.io.PrintStream strm)

Show caching statistics

showStats

public void showStats(java.io.PrintWriter strm)

Show caching statistics

addNotifier

public void addNotifier(FileCache.NotifyOnCommit notified)

Add to the list of objects to be notified before commit

Parameters:

notified - the obect to add to the list