package simpledb; import java.util.*; import java.io.*; /** * The interface for database files on disk. Each table is represented by a * single DbFile. DbFiles can fetch pages and iterate through tuples. Each * file has a unique id used to store metadata about the table in the Catalog. * DbFiles are generally accessed through the buffer pool, rather than directly * by operators. */ public interface DbFile { /** * Read the specified page from disk. * * @throws IllegalArgumentException if the page does not exist in this file. */ public Page readPage(PageId id); /** * Push the specified page to disk. * * @param p The page to write. page.getId().pageno() specifies the offset into the file where the page should be written. * @throws IOException if the write fails * */ public void writePage(Page p) throws IOException; /** * Inserts the specified tuple to the file on behalf of transaction. * This method will acquire a lock on the affected pages of the file, and * may block until the lock can be acquired. * * @param tid The transaction performing the update * @param t The tuple to add. This tuple should be updated to reflect that * it is now stored in this file. * @return An ArrayList contain the pages that were modified * @throws DbException if the tuple cannot be added * @throws IOException if the needed file can't be read/written */ public ArrayList insertTuple(TransactionId tid, Tuple t) throws DbException, IOException, TransactionAbortedException; /** * Removes the specified tuple from the file on behalf of the specified * transaction. * This method will acquire a lock on the affected pages of the file, and * may block until the lock can be acquired. * * @param tid The transaction performing the update * @param t The tuple to delete. This tuple should be updated to reflect that * it is no longer stored on any page. * @return An ArrayList contain the pages that were modified * @throws DbException if the tuple cannot be deleted or is not a member * of the file */ public ArrayList deleteTuple(TransactionId tid, Tuple t) throws DbException, IOException, TransactionAbortedException; /** * Returns an iterator over all the tuples stored in this DbFile. The * iterator must use {@link BufferPool#getPage}, rather than * {@link #readPage} to iterate through the pages. * * @return an iterator over all the tuples stored in this DbFile. */ public DbFileIterator iterator(TransactionId tid); /** * Returns a unique ID used to identify this DbFile in the Catalog. This id * can be used to look up the table via {@link Catalog#getDatabaseFile} and * {@link Catalog#getTupleDesc}. *

* Implementation note: you will need to generate this tableid somewhere, * ensure that each HeapFile has a "unique id," and that you always * return the same value for a particular HeapFile. A simple implementation * is to use the hash code of the absolute path of the file underlying * the HeapFile, i.e. f.getAbsoluteFile().hashCode(). * * @return an ID uniquely identifying this HeapFile. */ public int getId(); /** * Returns the TupleDesc of the table stored in this DbFile. * @return TupleDesc of this DbFile. */ public TupleDesc getTupleDesc(); }