Instructors: Winston Hsu, Hao-Hua Chu Fall 2009 HW4: Buffer Manager Instructors: Winston Hsu, Hao-Hua Chu Fall 2009

Architecture of a DBMS Query Query Optimization and Execution Relation Operators File and Access Methods Buffer Management Disk Space Management DB

Buffer Manager Simple Buffer Manager Structure Operations Pages in the buffer pool is not ordered in any way Hash table to figure out what frame a given disk page occupies Love/Hate buffer replace algorithm Operations bring a disk page into the buffer pool and pin it unpin a page in the buffer pool allocate/de-allocate pages on disk flush/flush all buffer page(s) into the disk page

Buffer Manager Memory Structure Buffer Page Description FrameDesc pageNo dirtyFlag pin_count numbuf Buffer Pool Page Buffer Hash Table pageNo frameNo *next …… HTSIZE ……

Love/Hate Replacement upper level user hints the buffer manager that the page is loved or hated. Replace hated pages first, then loved pages. MRU list for the hated pages, LRU list for the loved pages “ Love conquers hate “

Functions (in buf.h and buf.C) BufMgr Initializes buffer manager: create buffer pool, buffer pool description, hash table….etc. Malloc, calloc….. pinPage, unpinPage, newPage, freePage, flushPage, flushAllPages Use Minibase API Your own functions (if needed) For hash table and replacement policy

Minibase APIs Page Errors handling Status MINIBASE_DB->read_page(PageId pageno, Page* pageptr) Status MINIBASE_DB->write_page(PageId pageno, Page* pageptr) Status MINIBASE_DB->allocate_page(PageId& start_page_num, int run_size=1) Status MINIBASE_DB->deallocate_page(PageId start_page_num, int run_size=1) Errors handling status = MINIBASE_DB->write_page(pageid, &bufPool[i]); if (status != OK) { // status: OK or FAIL // your own error message }

Get Started Read the PDF for detail description. Group assignment (at most 2 people/group) Download BufMgr for source code. Read README.first before you strat. Post your questions on ptt.cc / CSIE_DBMS. Minibase homepage and Google