LRU Class Reference

#include <bm_policies.h>

Inheritance diagram for LRU:

Collaboration diagram for LRU:

Public Member Functions
	LRU (Frame *frame_table)
	LRU constructor. Initializes pointer to buffer manager's frame_table, creates the free list, sets queue, rep_calls, and avg_frames_checked to 0.
	~LRU ()
FrameId	replace ()
	Method that implements the Least Recently Used (LRU) replacement policy functionality.
void	pin (FrameId frame_id)
	Frame is being pinned with pin count going from 0 to 1. Frame id is removed from queue.
void	unpin (FrameId frame_id)
	Frame is being unpinned with pin count going from 1 to 0. Frame id is added to the bottom of the queue.
void	freeFrame (FrameId frame_id)
	The frame is invalidated in the buffer manager, and is added to the free list of frames in the replacement policy. frame_id is also removed from the queue.
void	printStats ()
	Prints replacement calls, average frames checked when pinning, and max and average size of queue.
Public Member Functions inherited from ReplacementPolicy
virtual	~ReplacementPolicy ()
	Empty Destructor.
virtual void	getRepStats (struct BufferState::ReplacementStats *rep_stats)
	Updates the struct of replacement policy statistics within the buffer state struct. Adds the replacement type, number of calls to the replacement policy, number of calls to getPage or allocatePage average frames checked by each call to policy, and the ref_bit count and clock_hand, which is irrelevant unless the policy is Clock Replacement.
void	printFrame (FrameId frame_id)
	THIS METHOD IS FOR DEBUGGING ONLY. Prints Frame state relevant to the replacement policy of a given FrameId, including pin count and ref_bit for Clock Replacement.
void	advanceCalls ()
	Increment new_page_calls by 1. Called in both allocatePage and getPage in BufferManager.

Private Member Functions
RepType	_getType ()
	Derived class from pure virtual function that returns replacement policy type specific to this derived class.

Private Attributes
std::list< FrameId >	queue
int	remove_calls

Additional Inherited Members
Protected Member Functions inherited from ReplacementPolicy
void	_createFree ()
	Creates a free list for the buffer pool by checking each frame in the buffer pool and checking if it is valid. Used in constructor of each replacement policy.
Protected Attributes inherited from ReplacementPolicy
Frame *	frame_table
std::queue< FrameId >	free
std::uint64_t	rep_calls
double	avg_frames_checked
std::uint64_t	new_page_calls

Detailed Description

SwatDB LRU Class. LRU is a derived class of ReplacementPolicy that manages the buffer replacement policy of the DBMS. The Least Recently Used (LRU) algorithm keeps a queue of unpinned pages, choosing the least recently unpinned page for replacement. It is a generally good policy, but it has more overhead than other policies.

Constructor & Destructor Documentation

LRU()

LRU::LRU

(

Frame *

frame_table

)

LRU constructor. Initializes pointer to buffer manager's frame_table, creates the free list, sets queue, rep_calls, and avg_frames_checked to 0.

Precondition

BufferManager constructor is being called, frame_table parameter points to an initialized frame_table object.

Postcondition

A LRU object will be initialized with member variables initialized.

Parameters

Frame

*frame_table, pointer to frame_table array of BufferManager.

~LRU()

LRU::~LRU

(

)

Empty Destructor.

Member Function Documentation

_getType()

RepType LRU::_getType ( )

privatevirtual

Derived class from pure virtual function that returns replacement policy type specific to this derived class.

Returns

RepType LruT.

Implements ReplacementPolicy.

freeFrame()

void LRU::freeFrame ( FrameId  frame_id )

virtual

The frame is invalidated in the buffer manager, and is added to the free list of frames in the replacement policy. frame_id is also removed from the queue.

Precondition

A page in the buffer pool has been deallocated.

Postcondition

frame_id is added to the free list and removed from the queue.

Parameters

FrameId

frame_id of the frame being set invalid.

Reimplemented from ReplacementPolicy.

pin()

void LRU::pin ( FrameId  frame_id )

virtual

Frame is being pinned with pin count going from 0 to 1. Frame id is removed from queue.

Precondition

A page in the buffer pool has been unpinned from pin count 1 to 0.

Postcondition

Frame id is removed from queue.

Parameters

FrameId

frame_id of the frame being unpinned.

Implements ReplacementPolicy.

printStats()

void LRU::printStats ( )

virtual

Prints replacement calls, average frames checked when pinning, and max and average size of queue.

Implements ReplacementPolicy.

replace()

FrameId LRU::replace ( )

virtual

Method that implements the Least Recently Used (LRU) replacement policy functionality.

Precondition

The replacement policy has been invoked. The buffer manager is attempting to add a frame to the buffer pool. The buffer map is locked.

Postcondition

If there is a free (invalid) frame, that FrameID is chosen for replacement and is returned. Else, the least recently unpinned frame is chosen and taken off the queue. If all pages are pinned, an exception is thrown.

Returns

FrameID of the frame that is eligible for replacement in the buffer pool.

Exceptions

InsufficientSpaceBufMgr

if all pages in the buffer pool are pinned.

Implements ReplacementPolicy.

unpin()

void LRU::unpin ( FrameId  frame_id )

virtual

Frame is being unpinned with pin count going from 1 to 0. Frame id is added to the bottom of the queue.

Precondition

A page in the buffer pool has been unpinned from pin count 1 to 0.

Postcondition

Frame id is added to the bottom of the queue.

Parameters

FrameId

frame_id of the frame being unpinned.

Implements ReplacementPolicy.

Member Data Documentation

queue

std::list<FrameId> LRU::queue

private

List that is used like a queue that holds all unpinned frames.

remove_calls

int LRU::remove_calls

private

Number of times frame has to be removed from stack. Used for calculating avg_frames_checked.

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

• bm_policies.h