Class BTreeFile

src/java/simpledb/index/BTreeFile.java:31–1306

BTreeFile is an implementation of a DbFile that stores a B+ tree. Specifically, it stores a pointer to a root page, a set of internal pages, and a set of leaf pages, which contain a collection of tuples in sorted order. BTreeFile works closely with BTreeLeafPage, BTreeInternalPage, and BTreeRootPtrP

 * @author Becca Taft
 */
public class BTreeFile implements DbFile {

	private final File f;
	private final TupleDesc td;
	private final int tableid;
	private final int keyField;

	/**
	 * Constructs a B+ tree file backed by the specified file.
	 * 
	 * @param f - the file that stores the on-disk backing store for this B+ tree
	 *            file.
	 * @param key - the field which index is keyed on
	 * @param td - the tuple descriptor of tuples in the file
	 */
	public BTreeFile(File f, int key, TupleDesc td) {
		this.f = f;
		this.tableid = f.getAbsoluteFile().hashCode();
		this.keyField = key;
		this.td = td;
	}

	/**
	 * Returns the File backing this BTreeFile on disk.
	 */
	public File getFile() {
		return f;
	}

	/**
	 * Returns an ID uniquely identifying this BTreeFile. Implementation note:
	 * you will need to generate this tableid somewhere and ensure that each
	 * BTreeFile has a "unique id," and that you always return the same value for
	 * a particular BTreeFile. We suggest hashing the absolute file name of the
	 * file underlying the BTreeFile, i.e. f.getAbsoluteFile().hashCode().
	 * 
	 * @return an ID uniquely identifying this BTreeFile.
	 */
	public int getId() {
		return tableid;
	}

	/**
	 * Returns the TupleDesc of the table stored in this DbFile.
	 * 
	 * @return TupleDesc of this DbFile.
	 */
	public TupleDesc getTupleDesc() {
		return td;
	}

	/**
	 * Read a page from the file on disk. This should not be called directly
	 * but should be called from the BufferPool via getPage()
	 * 
	 * @param pid - the id of the page to read from disk
	 * @return the page constructed from the contents on disk
	 */