1. Project Implementation of Buffer Management
CSED421: Database Systems Labs

2. Buffer Management DBMS is..
A gigantic software package combining all these modules!
Query Optimization and Execution
Relational Operator Evaluator
Files and Access Methods
Buffer Management
Disk Space Management
DBMS
Buffer Management

3. The Overview of BufMgr
Software layer responsible for bringing pages from disk to main memory as needed

4. Frame Information The frame has two variables.
pin_count: the number of current users of the page
dirty: indicate if the page has been modified.
Initially, the pin_count for every frame is set to 0, and the dirty bits are turned off.

5. When a Page is Requsted If a requested page is not in pool
Choose a frame for replacement.
If frame is dirty, write it to disk.
Read the requested page into a chosen frame.
Pin the page, and return its address
If requests can be predicted, e.g., sequential scans, pages can be pre-fetched several pages at a time.

6. Buffer Replacement Policy
Frame is chosen for replacement by a replacement policy:
Least-recently-used (LRU), clock replacement, First-in-first-out (FIFO), most recently used (MRU)
Policy can have big impact on # of I/Os; depends on the access pattern.

7. Clock Replacement Algorithm
Simple implementation
“Clock” had points to next page to replace
If R=0, replace the page.
If R=1, set R=0 and advance the clock hand.
Continue until the page with R=0 is found.
This may involve going all the way around the clock.

8. Source codes
8 cpp files
main.cpp, test.cpp, db.cpp, bmtest.cpp, db.cpp, page.cpp, bufmgr.cpp, clockreplacementpolicy.cpp
Only need to put more source codes for two files.
You may add some source codes to the other files.

9. Source codes Status UnpinPage( PageID pid, Bool dirty=FALSE );
class BufMgr {
public:
BufMgr( int bufsize );
~BufMgr();
Status PinPage( PageID pid, Page*& page, Bool emptyPage=FALSE );
Status UnpinPage( PageID pid, Bool dirty=FALSE );
Status NewPage( PageID& pid, Page*& firstpage,int howmany=1 );
Status FreePage( PageID pid );
Status FlushPage( PageID pid );
Status FlushAllPages();
Status ResetStat();
Status PrintStat();
unsigned int GetNumOfBuffers();
unsigned int GetNumOfUnpinnedBuffers();
private:
int mNumOfBuffers; // buffer size
Frame* mBufferPool; // data structure that represents all the frames in the buffer pool
HashTable<PageID> mLookupTable; // data structure that enables fast lookup for pids
std::queue<int> mFreeList; // queue of free pages in the buffer pool
ReplacementPolicy* mPolicy; // pointer to the replacement policy currently being used
int mNumPinRequests; // variable to store no. of requests
int mNumPinMisses; // variable to store no. of pin page misses
int mNumDirtyWrites; // variable to store no. of dirty page writes };

10. Source codes class ClockReplacementPolicy : public ReplacementPolicy {
ClockReplacementPolicy( Frame* bufPool, int poolSize );
~ClockReplacementPolicy(); // destructor that must deallocate storage for reference
virtual int GetFrame();
virtual void UpdateFrame( int index );
private:
int mCurrent; // represents which buffer frame is currently considered for replacement
bool * mReference; // data structure that stores the reference bits for each frame };

11. Results

12. Source codes Visual studio 2005 환경 Lab 2010 홈페이지에서 다운로드
질문 및 답변은 Lab 게시판을 참고
Textbook pp 참고

13. Submission & Deadline 제출 제출기한 소스코드 보고서 (10장 이내)
두 개의 파일 이외에 다른 코드 수정 시 수정한 이유와 파일 수정에 대해 서술할 것.
보고서 (10장 이내)
각 구현한 함수에 대한 간략한 서술
구현한 replacement policy에 대한 설명
Test 결과에 대한 설명 및 분석
제출기한
2010년 5월 21일 금요일 PM 18:00 공학 2동 306호
늦게 제출시 패널티 있음.

14. Q&A
Enjoy getting your hands dirty!!