#include <bufmgr.h>

Collaboration diagram for BufferManager:

[legend]

Public Member Functions
	BufferManager (DiskManager *disk_mgr)
	BufferManager constructor. Initializes the buf_pool and frame_table, and stores a pointer to SwatDB's DiskManager. More...

	~BufferManager ()
	BufferManager destructor. More...

std::pair< Page *, PageId >	allocatePage (FileId file_id)
	Allocates a Page for the file of given FileId. The Page is allocated both in the buffer pool, and on disk. More...

void	deallocatePage (PageId page_id)
	Removes the Page of the given PageId from the buffer pool, and deallocates the Page from the appopriate file on disk. More...

Page *	getPage (PageId page_id)
	Gets Page by page_id, pins the Page, and returns a pointer to the Page object. More...

void	releasePage (PageId page_id, bool dirty)
	Unpins a Page in the buffer pool. More...

void	setDirty (PageId page_id)
	Set the Page of the given PageId dirty. More...

void	flushPage (PageId page_id)
	Flushes the Page of the given PageId to disk. More...

void	createFile (FileId file_id)
	Calls createFile() method on the DiskManager to create new Unix file that corresponds to the given FileId. More...

void	removeFile (FileId file_id)
	Calls removeFile() method on the DiskManager. Checks that none of the file's pages are pinned in the buffer pool. Removes any of the file's pages from the buffer pool before removing from disk. More...

void	clearBuffer ()
	THIS METHOD IS FOR DEBUGGING ONLY. Clears the entire buffer pool, resetting all frames and removing pages from the buffer_map even if pinned. Does not flush any dirty pages either.

BufferState	getBufferState ()
	THIS METHOD IS FOR DEBUGGING ONLY. Returns the current state of the buffer pool. More...

void	printAllFrames ()
	THIS METHOD IS FOR DEBUGGING ONLY. Prints Frame state of every Frame in the buffer pool, including pin count, valid bit, dirty bit, and ref_bit. If Page is valid, PageId is printed.

void	printValidFrames ()
	THIS METHOD IS FOR DEBUGGING ONLY. Prints Frame state of every valid Frame in the buffer pool, including PageId, pin count, valid bit, dirty bit, and ref_bit.

void	printFrame (FrameId frame_id)
	THIS METHOD IS FOR DEBUGGING ONLY. Prints Frame state of given FrameId, including pin count, valid bit, dirty bit, and ref_bit. If Page is valid, PageId is printed.

void	printPage (PageId page_id)
	THIS METHOD IS FOR DEBUGGING ONLY. Prints Frame state of given PageId, including FrameId, pin count, valid bit, dirty bit, and ref_bit. If Page is not in the buffer map, prints "Page Not Found".

void	printBufferState ()
	THIS METHOD IS FOR DEBUGGING ONLY. Prints current buffer state, including total number of pages, number of valid pages, number of pinned pages, number of dirty pages, number of pages whose ref bit is set and the current clock hand position.

Private Member Functions
FrameId	_allocateFrame ()
	Allocates a Frame in the frame_table and returns the Frame index. More...

Private Attributes
BufferMap	buf_map

Frame	frame_table [BUF_SIZE]

Page	buf_pool [BUF_SIZE]

DiskManager *	disk_mgr

std::uint32_t	clock_hand

std::mutex	buf_map_mtx

Detailed Description

SwatDb BufferManager Class. BufferManager manages in memory space of DBMS at page level granularity. At higher level, pages of data could be allocated, deallocated, retrieved to memory and fliushed to disk, using various methods.

Constructor & Destructor Documentation

◆ BufferManager()

BufferManager::BufferManager ( DiskManager * disk_mgr )

BufferManager constructor. Initializes the buf_pool and frame_table, and stores a pointer to SwatDB's DiskManager.

Precondition: disk_mgr points to an initialized DiskManager object.

Postcondition: A BufferManager object will be initialized with an empty buffer pool. disk_mgr is set to the given DiskManager* and clock_hand is set to 0.

Parameters

disk_mgr A pointer to SwatDB's DiskManager object. (DiskManager*).

◆ ~BufferManager()

BufferManager::~BufferManager ( )

BufferManager destructor.

Precondition: None.

Postcondition: Every valid and dirty Page in buffer pool is written to disk.

Member Function Documentation

◆ _allocateFrame()

FrameId BufferManager::_allocateFrame ( )

private

Allocates a Frame in the frame_table and returns the Frame index.

Precondition: Not every Page in the buffer pool is pinned. buf_map mutex is locked.

Postcondition: If there is a Page that is not valid, its Frame is reset and FrameId is returned. If there is a Page that is valid, and is not referenced, it is selected for eviction. If the victim Page is dirty, it is written to disk. Then, the Frame is reset, PageId of the victim Page is removed from buf_map and FrameId is returned. In the process of performing the replacement algorithm, ref_bit of some valid pages that are not pinned may be set to false.

Returns: FrameId of the allocated Frame in frame_table.

Exceptions

InsufficientSpaceBufMgr If all pages in the buffer pool are pinned.

◆ allocatePage()

std::pair<Page*,PageId> BufferManager::allocatePage ( FileId file_id )

Allocates a Page for the file of given FileId. The Page is allocated both in the buffer pool, and on disk.

Precondition: A valid FileId is provided and there is a free Page on disk or there is enough space in Unix file. There is also free space in the buffer pool, or a Page which can be evicted from the buffer pool.

Postcondition: A Frame is allocated, and a corresponding Page in the buffer pool is allocated. The Frame's page_id is set, valid is set to true, and the pin_count is set to 1. The PageId is added to the BufferMap. Finally, a pair of a pointer to the allocated Page and PageId is returned.

Parameters

file_id A FileId to which a Page should be allocated.

Returns: std::pair of Page* and PageId of the allocated Page.

Exceptions

InsufficientSpaceBufMgr	If there is not enough space in buffer pool.
InvalidFileIdDiskMgr	If file_id not valid.
InsufficientSpaceDiskMgr	If there is not enough space in the Unix file.

◆ createFile()

void BufferManager::createFile ( FileId file_id )

Calls createFile() method on the DiskManager to create new Unix file that corresponds to the given FileId.

Precondition: FileId is valid.

Postcondition: Unix file that corresponds to the file_id is created.

Parameters

file_id FileId of the file to be created.

See also: DiskManager::createFile()

◆ deallocatePage()

void BufferManager::deallocatePage ( PageId page_id )

Removes the Page of the given PageId from the buffer pool, and deallocates the Page from the appopriate file on disk.

Precondition: A valid PageId of an unpinned Page is provided as a parameter.

Postcondition: If the Page is in the buffer pool, the Frame is reset, and the Page is removed from the buffer pool. The Page is deallocated from disk.

Parameters

pageId PageId of the Page to be deallocated

Exceptions

PagePinnedBufMgr	If the Page is pinned.
InvalidPageNumDiskMg	If page_id.page_num is invalid (from DiskManager layer)
InvalidFileIdDiskMgr	If page_id.file_id is invalid (from DiskManager layer)

◆ flushPage()

void BufferManager::flushPage ( PageId page_id )

Flushes the Page of the given PageId to disk.

Precondition: A PageId of a pinned Page is provided as input.

Postcondition: If the Page is set dirty, the Page is written to disk through the disk_mgr. Page is still pinned.

Parameters

page_id PageId of the Page to set dirty.

Exceptions

PageNotFoundBufMgr	If page_id not in buf_map.
InvalidFileIdDiskMgr	If page_id.file_id not valid.
InvalidPageNumDiskMgr	If page_id.page_num not valid.

◆ getBufferState()

BufferState BufferManager::getBufferState ( )

THIS METHOD IS FOR DEBUGGING ONLY. Returns the current state of the buffer pool.

See also: BufferState

◆ getPage()

Page* BufferManager::getPage ( PageId page_id )

Gets Page by page_id, pins the Page, and returns a pointer to the Page object.

Precondition: A PageId of an allocated Page is provided as a parameter and buffer pool is not full of pinned pages.

Postcondition: If the page_id is in buf_map, the Page is pinned and its pointer is returned. Else, a Frame is allocated in the buffer pool according to the page replacement policy, the Page is read from disk_mgr into the buffer pool, and the page_id, pin count, and valid bit are set. Page* is returned.

Parameters

page_id A PageId corresponding to the pointer to be returned.

Returns: Pointer to the Page with page_id.

Exceptions

InvalidPageIdBufMgr	If page_id is not valid.
InsufficientSpaceBufMgr	If buffer pool is full.
InvalidFileIdDiskMgr	from DiskManager if page_id.file_id invalid
InvalidPageNumDiskMgr	from DiskManger if page_id.page_num invalid
DiskErrorDiskMgr	frome DiskManager if file operation fails.

◆ releasePage()

void BufferManager::releasePage	(	PageId	page_id,
		bool	dirty
	)

Unpins a Page in the buffer pool.

Precondition: A PageId of a pinned Page is provided as input. The Page is in the buffer pool and is pinned by the executing thread/process.

Postcondition: The pin count of the Page is decremented. ref_bit is set to true. Dirty bit is set if the dirty parameter is true.

Parameters

page_id PageId of the Page to be released.

Exceptions

PageNotPinnedBufMgr	If Page is not pinned. (pin_count is 0).
PageNotFoundBufMgr	If page_id is not in buf_map.

◆ removeFile()

void BufferManager::removeFile ( FileId file_id )

Calls removeFile() method on the DiskManager. Checks that none of the file's pages are pinned in the buffer pool. Removes any of the file's pages from the buffer pool before removing from disk.

Precondition: A valid FileId is given as a parameter. None of the file's pages are pinned in the buffer pool.

Postcondition: If the file has pages in the buffer pool, the corresponding frames are reset and pages are removed from buf_map. The file is removed from disk via DiskManager->removeFile().

Parameters

file_id FileId of the file to be removed.

Exceptions

PagePinnedBufMgr If the are pinned pages of file_id.

See also: DiskManager::removeFile()

◆ setDirty()

void BufferManager::setDirty ( PageId page_id )

Set the Page of the given PageId dirty.

Precondition: A PageId of a pinned Page is provided as input.

Postcondition: The Page is set dirty.

Parameters

page_id PageId of the Page to set dirty.

Exceptions

PageNotFoundBufMgr If page_id is not in the buffer pool.

Member Data Documentation

◆ buf_map

BufferMap BufferManager::buf_map

private

A wrapper for std::unordered_map<PageId, FrameId> that maps PageIds to Frame indices in buf_pool. Has different methods from std::unordered_map. Have get(), contains(), insert(), and remove() methods.

◆ buf_map_mtx

std::mutex BufferManager::buf_map_mtx

private

std::mutex for synchronized access to buf_map.

◆ buf_pool

Page BufferManager::buf_pool[BUF_SIZE]

private

Array of Page objects. Represents the buffer pool.

◆ clock_hand

std::uint32_t BufferManager::clock_hand

private

Clock hand which is a std::uint32_t, corresponding to the index of a Frame in frame_table. Used for the clock replacement policy.

◆ disk_mgr

DiskManager* BufferManager::disk_mgr

private

Pointer to SwatDB's DiskManager. Used for reading, writing, allocating, and deallocating pages to disk.

◆ frame_table

Frame BufferManager::frame_table[BUF_SIZE]

private

Array of Frame objects. Frames store metadata about each Page in the buffer pool.

The documentation for this class was generated from the following file:

bufmgr.h

Public Member Functions

Private Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

◆ BufferManager()

◆ ~BufferManager()

Member Function Documentation

◆ _allocateFrame()

◆ allocatePage()

◆ createFile()

◆ deallocatePage()

◆ flushPage()

◆ getBufferState()

◆ getPage()

◆ releasePage()

◆ removeFile()

◆ setDirty()

Member Data Documentation

◆ buf_map

◆ buf_map_mtx

◆ buf_pool

◆ clock_hand

◆ disk_mgr

◆ frame_table