BufferManager Class Reference

#include <BufferManager.h>

List of all members.

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Detailed Description

Buffer manager.

Manages a memory-based buffer pool of pages.

Author:

Dave Musicant, with considerable material reused from the UW-Madison Minibase project

Public Member Functions
	BufferManager (int poolSize)
	Creates a buffer manager with the specified size.
	~BufferManager ()
	Destructor.
int	getPoolSize ()
	Returns the pool size.
Page *	pinPage (int pinPageId, string fileName, bool emptyPage)
	Checks if this page is in buffer pool.
void	unpinPage (int unpinPageId, string fileName, bool dirty)
	If the pin count for this page is greater than 0, it is decremented.
int	newPage (int numPages, string fileName, Page *&firstPage)
	Requests a run of pages from the underlying database, then finds a frame in the buffer pool for the first page and pins it.
void	freePage (int pageId, string fileName)
	Deallocates a page from the underlying database.
void	flushPage (int pageId, string fileName)
	Flushes page from the buffer pool to the underlying database if it is dirty.
void	flushAllPages ()
	Flushes all dirty pages from the buffer pool to the underlying databases.
int	findFrame (int pageId, string fileName)
	Returns buffer pool location for a particular pageId.
Static Public Attributes
static const int	INVALID_PAGE = -1
	Value to use for an invalid page id.
Classes
class	FrameDescriptor

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Constructor & Destructor Documentation

BufferManager::BufferManager

(

int

poolSize

)

Creates a buffer manager with the specified size.

Parameters:

poolSize

the number of pages that the buffer pool can hold.

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Member Function Documentation

int BufferManager::findFrame	(	int	pageId,
		string	fileName
	)

Returns buffer pool location for a particular pageId.

This method is just used for testing purposes: it probably doesn't serve a real purpose in an actual database system.

Parameters:

	pageId	the page id to be looked up.
	fileName	the file name to be looked up.

Returns:

the frame location for the page of interested. Returns -1 if the page is not in the pool.

void BufferManager::flushAllPages

(

)

Flushes all dirty pages from the buffer pool to the underlying databases.

If page is not dirty, it is not flushed, especially since an undirty page may hang around even after the underlying database has been erased.

void BufferManager::flushPage	(	int	pageId,
		string	fileName
	)

Flushes page from the buffer pool to the underlying database if it is dirty.

If page is not dirty, it is not flushed, especially since an undirty page may hang around even after the underlying database has been erased. If the page is not in the buffer pool, do nothing, since the page is effectively flushed already.

Parameters:

	pageId	the page id to be flushed.
	fileName	the name of the database from where the page is to be deallocated.

void BufferManager::freePage	(	int	pageId,
		string	fileName
	)

Deallocates a page from the underlying database.

Verifies that page is not pinned.

Parameters:

	pageId	the page id to be deallocated.
	fileName	the name of the database from where the page is to be deallocated.

Exceptions:

PagePinnedException

if the page is pinned

int BufferManager::getPoolSize

(

)

Returns the pool size.

Returns:

the pool size.

int BufferManager::newPage	(	int	numPages,
		string	fileName,
		Page *&	firstPage
	)

Requests a run of pages from the underlying database, then finds a frame in the buffer pool for the first page and pins it.

If the buffer pool is full, no new pages are allocated from the database.

Parameters:

	numPages	the number of pages in the run to be allocated.
	fileName	the name of the database from where pages are to be allocated.
	firstPage	a pointer to a page which will be replaced with a pointer to the actual page in the buffer pool.

Returns:

the first page id of the run. Returns INVALID_PAGE if there is not enough space in the buffer pool for the requested run.

Exceptions:

FileFullException

if there are not enough free pages (passed through from DBFile).

Page* BufferManager::pinPage	(	int	pinPageId,
		string	fileName,
		bool	emptyPage
	)

Checks if this page is in buffer pool.

If it is, returns a pointer to it. Otherwise, it finds an available frame for this page, reads the page, and pins it. Writes out the old page, if it is dirty, before reading.

Parameters:

	pinPageId	the page id for the page to be pinned
	fileName	the name of the database that contains the page to be pinned
	emptyPage	determines if the page is known to be empty. If true, then the page is not actually read from disk since it is assumed to be empty.

Returns:

a pointer to the page in the buffer pool. If the buffer pool is full, NULL is returned.

void BufferManager::unpinPage	(	int	unpinPageId,
		string	fileName,
		bool	dirty
	)

If the pin count for this page is greater than 0, it is decremented.

If the pin count becomes zero, it is appropriately included in a group of replacement candidates.

Parameters:

	unpinPageId	the page id for the page to be unpinned
	fileName	the name of the database that contains the page to be unpinned
	dirty	if false, then the page does not actually need to be written back to disk.

Exceptions:

	InvalidPageException	if unpinPageNum is not valid.
	PageNotPinnedException	if the page is not pinned, or if the page id is invalid in some other way.

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