chap file processing and external sorting buffer pool' logical storage space physicallyit will actually be copied to the appropriate byte position in some buffer in the buffer pool example assume each sector of the disk file (and thus each block in the buffer poolstores bytes assume that the buffer pool is in the state shown in figure if the next request is to copy bytes beginning at position of the filethese bytes should be placed into sector (whose bytes go from position to position because sector is currently in the buffer poolwe simply copy the bytes contained in space to byte positions - the buffer containing sector is then moved to the buffer pool ahead of the buffer containing sector the alternative approach is to have the buffer pool provide to the user direct pointer to buffer that contains the necessary information such an interface might look as follows/*adt for buffer pools using the buffer-passing style *public interface bufferpooladt /*return pointer to the requested block *public byte[getblock(int block)/*set the dirty bit for the buffer holding "block*public void dirtyblock(int block)/tell the size of buffer public int blocksize()}in this approachthe user of the buffer pool is made aware that the storage space is divided into blocks of given sizewhere each block is the size of buffer the user requests specific blocks from the buffer poolwith pointer to the buffer holding the requested block being returned to the user the user might then read from or write to this space if the user writes to the spacethe buffer pool must be informed of this fact the reason is thatwhen given block is to be removed from the buffer poolthe contents of that block must be written to the backing storage if it has been modified if the block has not been modifiedthen it is unnecessary to write it out example we wish to write bytes beginning at logical position in the file assume that the buffer pool is in the state shown in figure using the second adtthe client would need to know that blocks (buffersare of size and therefore would request access to sector