simpledb.buffer
Class BasicBufferMgr

java.lang.Object
  simpledb.buffer.BasicBufferMgr

 class BasicBufferMgr
extends java.lang.Object

Manages the pinning and unpinning of buffers to blocks.

Author:

Edward Sciore

Constructor Summary

BasicBufferMgr(int numbuffs)
Creates a buffer manager having the specified number of buffer slots.

Method Summary

(package private) int	available() Returns the number of available (i.e.
(package private) void	flushAll(int txnum) Flushes the dirty buffers modified by the specified transaction.
(package private) Buffer	pin(Block blk) Pins a buffer to the specified block.
(package private) Buffer	pinNew(java.lang.String filename, PageFormatter fmtr) Allocates a new block in the specified file, and pins a buffer to it.
(package private) void	unpin(Buffer buff) Unpins the specified buffer.

Methods inherited from class java.lang.Object

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

Constructor Detail

BasicBufferMgr

BasicBufferMgr(int numbuffs)

Creates a buffer manager having the specified number of buffer slots. This constructor depends on both the FileMgr and LogMgr objects that it gets from the class SimpleDB. Those objects are created during system initialization. Thus this constructor cannot be called until SimpleDB.initFileAndLogMgr(String) or is called first.

Parameters:

numbuffs - the number of buffer slots to allocate

Method Detail

flushAll

void flushAll(int txnum)

Flushes the dirty buffers modified by the specified transaction.

Parameters:

txnum - the transaction's id number

pin

Buffer pin(Block blk)

Pins a buffer to the specified block. If there is already a buffer assigned to that block then that buffer is used; otherwise, an unpinned buffer from the pool is chosen. Returns a null value if there are no available buffers.

Parameters:

blk - a reference to a disk block

Returns:

the pinned buffer

pinNew

Buffer pinNew(java.lang.String filename,
              PageFormatter fmtr)

Allocates a new block in the specified file, and pins a buffer to it. Returns null (without allocating the block) if there are no available buffers.

Parameters:

filename - the name of the file

fmtr - a pageformatter object, used to format the new block

Returns:

the pinned buffer

unpin

void unpin(Buffer buff)

Unpins the specified buffer.

Parameters:

buff - the buffer to be unpinned

available

int available()

Returns the number of available (i.e. unpinned) buffers.

Returns:

the number of available buffers