BufferManager implements a steal and no-force buffer pool with a fixed number of page frames to buffer the pages in the regular files. More...

#include <storage/BufferManager.h>

Public Member Functions
	BufferManager ()
	Constructs a buffer manager that is uninitialized. More...

	~BufferManager ()
	Destructs a buffer manager in any valid or invalid state. More...

void	Init (BufferId buffer_size)
	Initializes a buffer manager. More...

void	Destroy ()
	Flushes all dirty pages back to disk and destroys the buffer manager. More...

BufferId	PinPage (PageNumber pid, char **frame)
	Pins the page in a buffer frame and sets `*frame` to the buffer frame (you may assume `frame` is never a `nullptr`). More...

BufferId	PinPage (PageNumber pid, char **frame, FileId expected_fid)
	This overload of PinPage() calls the two-argument overload first and then additionally whether the pinned page belong to the file with `expected_fid`. More...

void	UnpinPage (BufferId bufid)
	Unpins the buffered page. More...

void	UnpinPage (ScopedBufferId &bufid)
	Unpins the buffered page. More...

BufferId	LatchPage (BufferId bufid, LatchMode mode)
	You may ignore this function since we won't be implementing concurrency control and recovery. More...

void	UnlatchPage (BufferId bufid)
	You may ignore this function since we won't be implementing concurrency control and recovery. More...

void	UnlatchPage (ScopedBufferLatch bufid)
	You may ignore this function since we won't be implementing concurrency control and recovery. More...

void	MarkDirty (BufferId bufid)
	Marks a buffered page as dirty. More...

PageNumber	GetPageNumber (BufferId bufid) const
	Returns the page number of the pinned page in the specified buffer frame. More...

char *	GetBuffer (BufferId bufid) const
	Returns a pointer to the buffer frame with the given buffer ID. More...

Private Member Functions
void	Flush ()
	Flushes all dirty page back to disk. More...

BufferId	GetFreeFrame ()

Private Attributes
bool	initialized

absl::flat_hash_map< PageNumber, BufferId >	lookup_table

BufferId	n

BufferId	clock_hand

BufferMeta *	metas

char *	buffer_frames

Detailed Description

BufferManager implements a steal and no-force buffer pool with a fixed number of page frames to buffer the pages in the regular files.

It should track which page is currently pinned and how many times it is currently pinned, as well as whether it is dirty. When someone requests a pin on a page, it should return either an existing buffer frame that buffers the page, or returns a free buffer frame (possibly evicting some clean pages) and reads the page from the file manager into the buffer frame.

A note on buffer Id assignment: all valid values of the type BufferId except INVALID_BUFID may be used for denote a buffer frame. There's no restriction on how to assign BufferId values to each buffer frame (meaning you could use any subset of values to denote the buffer frames). However, the implementation should guarantee that, given the same buffer pool size, 1) the same buffer frame is always denoted with the same buffer ID in a BufferManager instance (i.e., the same buffer frame should be denoted with the same buffer ID regardless what page it is holding); 2) and the set of valid buffer ID stays the same in different BufferManager instances (i.e., a valid (resp. invaild) buffer ID in a BufferManager should also be valid (resp. invalid) in a BufferManager initialized with the same buffer pool size).

You may ignore any latch related functions since we won't be implementing concurrency control and recovery.

Constructor & Destructor Documentation

◆ BufferManager()

taco::BufferManager::BufferManager ( )

Constructs a buffer manager that is uninitialized.

It must not throw any error.

◆ ~BufferManager()

taco::BufferManager::~BufferManager ( )

Destructs a buffer manager in any valid or invalid state.

It must not throw any error.

Member Function Documentation

◆ Destroy()

void taco::BufferManager::Destroy ( )

Flushes all dirty pages back to disk and destroys the buffer manager.

This may perform clean ups that may fail and throw errors (such as Flush()), in which case, the buffer manager is in an undefined state. After calling Destroy(), one can only invoke the destructor on the buffer manager.

This should not fail when a previous Init() call fails or Init() was never called. However, it is undefined to call Destroy() more than once.

◆ Flush()

void taco::BufferManager::Flush ( )

private

Flushes all dirty page back to disk.

If there's still some page with a non-zero pin count, it throws a fatal error.

Note: this is only used for shutting down the database or testing, when we are sure no pin is supposed to be held.

◆ GetBuffer()

char * taco::BufferManager::GetBuffer ( BufferId bufid ) const

Returns a pointer to the buffer frame with the given buffer ID.

It is the same as the pointer stored in *frame in the previous BufferManager::PinPage() call that returns the bufid. Throws a fatal error if the buffer is not pinned. However, it is undefined if bufid is invalid or the buffer is not pinned by the calling thread.

◆ GetFreeFrame()

BufferId taco::BufferManager::GetFreeFrame ( )

private

◆ GetPageNumber()

PageNumber taco::BufferManager::GetPageNumber ( BufferId bufid ) const

Returns the page number of the pinned page in the specified buffer frame.

Throws a fatal error if the buffer is not pinned. However, it is undefined if bufid is invalid or the buffer is not pinned by the calling thread.

◆ Init()

void taco::BufferManager::Init ( BufferId buffer_size )

Initializes a buffer manager.

It may throw errors, in which case, the buffer manager is uninitialized and only the destructor may be called.

Note: the buffer frames should be aligned to 512-byte boundries so that they can be used for O_DIRECT I/O (see man 2 open).

It is undefined to call Init() more than once.

◆ LatchPage()

BufferId taco::BufferManager::LatchPage	(	BufferId	bufid,
		LatchMode	mode
	)

You may ignore this function since we won't be implementing concurrency control and recovery.

◆ MarkDirty()

void taco::BufferManager::MarkDirty ( BufferId bufid )

Marks a buffered page as dirty.

Throws a fatal error if the buffer is not pinned. However, it is undefined if bufid is invalid or the buffer is not pinned by the calling thread.

◆ PinPage() [1/2]

BufferId taco::BufferManager::PinPage	(	PageNumber	pid,
		char **	frame
	)

Pins the page in a buffer frame and sets *frame to the buffer frame (you may assume frame is never a nullptr).

Then it returns the Buffer ID of the buffer frame where the requested page is pinned.

PinPage() should always prefer an unpinned empty frame. If there's no free buffer frame, it should try to evict an unpinned page from the buffer. If the page is dirty, it should be written to the disk before it is evicted. It is an error if all buffer frames are pinned. It may also throw other errors due to I/O errors in the underlying files. In either case, the buffer manager should still be in a valid state.

◆ PinPage() [2/2]

BufferId taco::BufferManager::PinPage	(	PageNumber	pid,
		char **	frame,
		FileId	expected_fid
	)

This overload of PinPage() calls the two-argument overload first and then additionally whether the pinned page belong to the file with expected_fid.

If not, no page is pinned and it returns an INVALID_BUFID. The value of *frame is also not modified. Otherwise, it returns the buffer ID of the buffer frame with the requested page pinned and sets *frame to the buffer frame.

This is mainly used for testing and debugging but you may also use this overload where appropriate. You do not need to implement it.

◆ UnlatchPage() [1/2]

void taco::BufferManager::UnlatchPage ( BufferId bufid )

You may ignore this function since we won't be implementing concurrency control and recovery.

◆ UnlatchPage() [2/2]

void taco::BufferManager::UnlatchPage ( ScopedBufferLatch bufid )

inline

You may ignore this function since we won't be implementing concurrency control and recovery.

◆ UnpinPage() [1/2]

void taco::BufferManager::UnpinPage ( BufferId bufid )

Unpins the buffered page.

Throws a fatal error if the buffer is not pinned. However, it is undefined if bufid is invalid or the buffer is not pinned by the calling thread. It should not throw a non-fatal error.

◆ UnpinPage() [2/2]

void taco::BufferManager::UnpinPage ( ScopedBufferId & bufid )

inline

Unpins the buffered page.

Throws a fatal error if the buffer is not pinned. However, it is undefined if bufid is invalid or the buffer is not pinned by the calling thread. It should not throw a non-fatal error.

This overload prevents double unpin when someone calls BufferManager::UnpinPage on a ScopedBufferId.

Member Data Documentation

◆ buffer_frames

char* taco::BufferManager::buffer_frames

private

◆ clock_hand

BufferId taco::BufferManager::clock_hand

private

◆ initialized

bool taco::BufferManager::initialized

private

◆ lookup_table

absl::flat_hash_map<PageNumber, BufferId> taco::BufferManager::lookup_table

private

◆ metas

BufferMeta* taco::BufferManager::metas

private

◆ n

BufferId taco::BufferManager::n

private

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

Public Member Functions

Private Member Functions

Private Attributes

Detailed Description

Constructor & Destructor Documentation

◆ BufferManager()

◆ ~BufferManager()

Member Function Documentation

◆ Destroy()

◆ Flush()

◆ GetBuffer()

◆ GetFreeFrame()

◆ GetPageNumber()

◆ Init()

◆ LatchPage()

◆ MarkDirty()

◆ PinPage() [1/2]

◆ PinPage() [2/2]

◆ UnlatchPage() [1/2]

◆ UnlatchPage() [2/2]

◆ UnpinPage() [1/2]

◆ UnpinPage() [2/2]

Member Data Documentation

◆ buffer_frames

◆ clock_hand

◆ initialized

◆ lookup_table

◆ metas

◆ n