bufmgr
Class BufMgr

java.lang.Object
  bufmgr.BufMgr

All Implemented Interfaces:

GlobalConst

public class BufMgr

extends java.lang.Object

implements GlobalConst

The buffer manager class, it allocates new pages for the buffer pool, pins and unpins the frame, frees the frame page, and uses the replacement algorithm to replace the page.

Field Summary

Fields inherited from interface global.GlobalConst

INVALID_PAGE, MAX_NAME, MAX_SPACE, MAXATTRNAME, MAXFILENAME, MAXINDEXNAME, MINIBASE_BUFFER_POOL_SIZE, MINIBASE_DB_SIZE, MINIBASE_DEFAULT_SHAREDMEM_SIZE, MINIBASE_MAX_TRANSACTIONS, MINIBASE_MAXARRSIZE, MINIBASE_PAGESIZE, NUMBUF

Constructor Summary

BufMgr(int numbufs, java.lang.String replacerArg)
Create a buffer manager object.

Method Summary

void	flushAllPages() Flushes all pages of the buffer pool to disk
void	flushPage(PageId pageid) Added to flush a particular page of the buffer pool to disk
bufmgr.FrameDesc[]	frameTable() A few routines currently need direct access to the FrameTable.
void	freePage(PageId globalPageId) User should call this method if she needs to delete a page.
int	getNumBuffers() Gets the total number of buffers.
int	getNumUnpinnedBuffers() Gets the total number of unpinned buffer frames.
PageId	newPage(Page firstpage, int howmany) Call DB object to allocate a run of new pages and find a frame in the buffer pool for the first page and pin it.
void	pinPage(PageId pin_pgid, Page page, boolean emptyPage) Check if this page is in buffer pool, otherwise find a frame for this page, read in and pin it.
void	unpinPage(PageId PageId_in_a_DB, boolean dirty) To unpin a page specified by a pageId.

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

BufMgr

public BufMgr(int numbufs,
              java.lang.String replacerArg)

Create a buffer manager object.

Parameters:

numbufs - number of buffers in the buffer pool.

replacerArg - name of the buffer replacement policy.

Method Detail

pinPage

public void pinPage(PageId pin_pgid,
                    Page page,
                    boolean emptyPage)
             throws ReplacerException,
                    HashOperationException,
                    PageUnpinnedException,
                    InvalidFrameNumberException,
                    PageNotReadException,
                    BufferPoolExceededException,
                    PagePinnedException,
                    BufMgrException,
                    java.io.IOException

Check if this page is in buffer pool, otherwise find a frame for this page, read in and pin it. Also write out the old page if it's dirty before reading if emptyPage==TRUE, then actually no read is done to bring the page in.

Parameters:

page - the pointer poit to the page.

emptyPage - true (empty page); false (non-empty page)

Throws:

ReplacerException - if there is a replacer error.

HashOperationException - if there is a hashtable error.

PageUnpinnedException - if there is a page that is already unpinned.

InvalidFrameNumberException - if there is an invalid frame number .

PageNotReadException - if a page cannot be read.

BufferPoolExceededException - if the buffer pool is full.

PagePinnedException - if a page is left pinned .

BufMgrException - other error occured in bufmgr layer

java.io.IOException - if there is other kinds of I/O error.

unpinPage

public void unpinPage(PageId PageId_in_a_DB,
                      boolean dirty)
               throws ReplacerException,
                      PageUnpinnedException,
                      HashEntryNotFoundException,
                      InvalidFrameNumberException

To unpin a page specified by a pageId. If pincount>0, decrement it and if it becomes zero, put it in a group of replacement candidates. if pincount=0 before this call, return error.

Parameters:

dirty - the dirty bit of the frame

Throws:

ReplacerException - if there is a replacer error.

PageUnpinnedException - if there is a page that is already unpinned.

InvalidFrameNumberException - if there is an invalid frame number .

HashEntryNotFoundException - if there is no entry of page in the hash table.

newPage

public PageId newPage(Page firstpage,
                      int howmany)
               throws BufferPoolExceededException,
                      HashOperationException,
                      ReplacerException,
                      HashEntryNotFoundException,
                      InvalidFrameNumberException,
                      PagePinnedException,
                      PageUnpinnedException,
                      PageNotReadException,
                      BufMgrException,
                      DiskMgrException,
                      java.io.IOException

Call DB object to allocate a run of new pages and find a frame in the buffer pool for the first page and pin it. If buffer is full, ask DB to deallocate all these pages and return error (null if error).

Parameters:

firstpage - the address of the first page.

howmany - total number of allocated new pages.

Returns:

the first page id of the new pages.

Throws:

BufferPoolExceededException - if the buffer pool is full.

HashOperationException - if there is a hashtable error.

ReplacerException - if there is a replacer error.

HashEntryNotFoundException - if there is no entry of page in the hash table.

InvalidFrameNumberException - if there is an invalid frame number.

PageUnpinnedException - if there is a page that is already unpinned.

PagePinnedException - if a page is left pinned.

PageNotReadException - if a page cannot be read.

java.io.IOException - if there is other kinds of I/O error.

BufMgrException - other error occured in bufmgr layer

DiskMgrException - other error occured in diskmgr layer

freePage

public void freePage(PageId globalPageId)
              throws InvalidBufferException,
                     ReplacerException,
                     HashOperationException,
                     InvalidFrameNumberException,
                     PageNotReadException,
                     BufferPoolExceededException,
                     PagePinnedException,
                     PageUnpinnedException,
                     HashEntryNotFoundException,
                     BufMgrException,
                     DiskMgrException,
                     java.io.IOException

User should call this method if she needs to delete a page. this routine will call DB to deallocate the page.

Parameters:

globalPageId - the page number in the data base.

Throws:

InvalidBufferException - if buffer pool corrupted.

ReplacerException - if there is a replacer error.

HashOperationException - if there is a hash table error.

InvalidFrameNumberException - if there is an invalid frame number.

PageNotReadException - if a page cannot be read.

BufferPoolExceededException - if the buffer pool is already full.

PagePinnedException - if a page is left pinned.

PageUnpinnedException - if there is a page that is already unpinned.

HashEntryNotFoundException - if there is no entry of page in the hash table.

java.io.IOException - if there is other kinds of I/O error.

BufMgrException - other error occured in bufmgr layer

DiskMgrException - other error occured in diskmgr layer

flushPage

public void flushPage(PageId pageid)
               throws HashOperationException,
                      PageUnpinnedException,
                      PagePinnedException,
                      PageNotFoundException,
                      BufMgrException,
                      java.io.IOException

Added to flush a particular page of the buffer pool to disk

Parameters:

pageid - the page number in the database.

Throws:

HashOperationException - if there is a hashtable error.

PageUnpinnedException - if there is a page that is already unpinned.

PagePinnedException - if a page is left pinned.

PageNotFoundException - if a page is not found.

BufMgrException - other error occured in bufmgr layer

java.io.IOException - if there is other kinds of I/O error.

flushAllPages

public void flushAllPages()
                   throws HashOperationException,
                          PageUnpinnedException,
                          PagePinnedException,
                          PageNotFoundException,
                          BufMgrException,
                          java.io.IOException

Flushes all pages of the buffer pool to disk

Throws:

HashOperationException - if there is a hashtable error.

PageUnpinnedException - if there is a page that is already unpinned.

PagePinnedException - if a page is left pinned.

PageNotFoundException - if a page is not found.

BufMgrException - other error occured in bufmgr layer

java.io.IOException - if there is other kinds of I/O error.

getNumBuffers

public int getNumBuffers()

Gets the total number of buffers.

Returns:

total number of buffer frames.

getNumUnpinnedBuffers

public int getNumUnpinnedBuffers()

Gets the total number of unpinned buffer frames.

Returns:

total number of unpinned buffer frames.

frameTable

public bufmgr.FrameDesc[] frameTable()

A few routines currently need direct access to the FrameTable.