HeapPage.java 8.93 KiB
package simpledb;
import java.util.*;
import java.io.*;
/**
* Each instance of HeapPage stores data for one page of HeapFiles and
* implements the Page interface that is used by BufferPool.
*
* @see HeapFile
* @see BufferPool
*
*/
public class HeapPage implements Page {
final HeapPageId pid;
final TupleDesc td;
final byte header[];
final Tuple tuples[];
final int numSlots;
byte[] oldData;
private final Byte oldDataLock=new Byte((byte)0);
/**
* Create a HeapPage from a set of bytes of data read from disk.
* The format of a HeapPage is a set of header bytes indicating
* the slots of the page that are in use, some number of tuple slots.
* Specifically, the number of tuples is equal to: <p>
* floor((BufferPool.getPageSize()*8) / (tuple size * 8 + 1))
* <p> where tuple size is the size of tuples in this
* database table, which can be determined via {@link Catalog#getTupleDesc}.
* The number of 8-bit header words is equal to:
* <p>
* ceiling(no. tuple slots / 8)
* <p>
* @see Database#getCatalog
* @see Catalog#getTupleDesc
* @see BufferPool#getPageSize()
*/
public HeapPage(HeapPageId id, byte[] data) throws IOException {
this.pid = id;
this.td = Database.getCatalog().getTupleDesc(id.getTableId());
this.numSlots = getNumTuples();
DataInputStream dis = new DataInputStream(new ByteArrayInputStream(data));
// allocate and read the header slots of this page
header = new byte[getHeaderSize()];
for (int i=0; i<header.length; i++)
header[i] = dis.readByte();
tuples = new Tuple[numSlots];
try{
// allocate and read the actual records of this page
for (int i=0; i<tuples.length; i++)
tuples[i] = readNextTuple(dis,i);
}catch(NoSuchElementException e){
e.printStackTrace();
}
dis.close();
setBeforeImage();
}
/** Retrieve the number of tuples on this page.
@return the number of tuples on this page
*/
private int getNumTuples() {
// some code goes here
return 0;
}
/**
* Computes the number of bytes in the header of a page in a HeapFile with each tuple occupying tupleSize bytes
* @return the number of bytes in the header of a page in a HeapFile with each tuple occupying tupleSize bytes
*/
private int getHeaderSize() {
// some code goes here
return 0;
}
/** Return a view of this page before it was modified
-- used by recovery */
public HeapPage getBeforeImage(){
// not necessary for this assignment
return null;
}
public void setBeforeImage() {
synchronized(oldDataLock)
{
oldData = getPageData().clone();
}
}
/**
* @return the PageId associated with this page.
*/
public HeapPageId getId() {
// some code goes here
throw new UnsupportedOperationException("implement this");
}
/**
* Suck up tuples from the source file.
*/
private Tuple readNextTuple(DataInputStream dis, int slotId) throws NoSuchElementException {
// if associated bit is not set, read forward to the next tuple, and
// return null.
if (!isSlotUsed(slotId)) {
for (int i=0; i<td.getSize(); i++) {
try {
dis.readByte();
} catch (IOException e) {
throw new NoSuchElementException("error reading empty tuple");
}
}
return null;
}
// read fields in the tuple
Tuple t = new Tuple(td);
RecordId rid = new RecordId(pid, slotId);
t.setRecordId(rid);
try {
for (int j=0; j<td.numFields(); j++) {
Field f = td.getFieldType(j).parse(dis);
t.setField(j, f);
}
} catch (java.text.ParseException e) {
e.printStackTrace();
throw new NoSuchElementException("parsing error!");
}
return t;
}
/**
* Generates a byte array representing the contents of this page.
* Used to serialize this page to disk.
* <p>
* The invariant here is that it should be possible to pass the byte
* array generated by getPageData to the HeapPage constructor and
* have it produce an identical HeapPage object.
*
* @see #HeapPage
* @return A byte array correspond to the bytes of this page.
*/
public byte[] getPageData() {
int len = BufferPool.getPageSize();
ByteArrayOutputStream baos = new ByteArrayOutputStream(len);
DataOutputStream dos = new DataOutputStream(baos);
// create the header of the page
for (int i=0; i<header.length; i++) {
try {
dos.writeByte(header[i]);
} catch (IOException e) {
// this really shouldn't happen
e.printStackTrace();
}
}
// create the tuples
for (int i=0; i<tuples.length; i++) {
// empty slot
if (!isSlotUsed(i)) {
for (int j=0; j<td.getSize(); j++) {
try {
dos.writeByte(0);
} catch (IOException e) {
e.printStackTrace();
}
}
continue;
}
// non-empty slot
for (int j=0; j<td.numFields(); j++) {
Field f = tuples[i].getField(j);
try {
f.serialize(dos);
} catch (IOException e) {
e.printStackTrace();
}
}
}
// padding
int zerolen = BufferPool.getPageSize() - (header.length + td.getSize() * tuples.length); //- numSlots * td.getSize();
byte[] zeroes = new byte[zerolen];
try {
dos.write(zeroes, 0, zerolen);
} catch (IOException e) {
e.printStackTrace();
}
try {
dos.flush();
} catch (IOException e) {
e.printStackTrace();
}
return baos.toByteArray(); }
/**
* Static method to generate a byte array corresponding to an empty
* HeapPage.
* Used to add new, empty pages to the file. Passing the results of
* this method to the HeapPage constructor will create a HeapPage with
* no valid tuples in it.
*
* @return The returned ByteArray.
*/
public static byte[] createEmptyPageData() {
int len = BufferPool.getPageSize();
return new byte[len]; //all 0
}
/**
* Delete the specified tuple from the page; the tuple should be updated to reflect
* that it is no longer stored on any page.
* @throws DbException if this tuple is not on this page, or tuple slot is
* already empty.
* @param t The tuple to delete
*/
public void deleteTuple(Tuple t) throws DbException {
// some code goes here
// not necessary for this assignment
}
/**
* Adds the specified tuple to the page; the tuple should be updated to reflect
* that it is now stored on this page.
* @throws DbException if the page is full (no empty slots) or tupledesc
* is mismatch.
* @param t The tuple to add.
*/
public void insertTuple(Tuple t) throws DbException {
// some code goes here
// not necessary for this assignment
}
/**
* Marks this page as dirty/not dirty and record that transaction
* that did the dirtying
*/
public void markDirty(boolean dirty, TransactionId tid) {
// some code goes here
// not necessary for this assignment
}
/**
* Returns the tid of the transaction that last dirtied this page, or null if the page is not dirty
*/
public TransactionId isDirty() {
// some code goes here
// not necessary for this assignment
return null;
}
/**
* Returns the number of empty slots on this page.
*/
public int getNumEmptySlots() {
// some code goes here
return 0;
}
/**
* Returns true if associated slot on this page is filled.
*/
public boolean isSlotUsed(int i) { // some code goes here
return false;
}
/**
* Abstraction to fill or clear a slot on this page.
*/
private void markSlotUsed(int i, boolean value) {
// some code goes here
// not necessary for this assignment
}
/**
* @return an iterator over all tuples on this page (calling remove on this iterator throws an UnsupportedOperationException)
* (note that this iterator shouldn't return tuples in empty slots!)
*/
public Iterator<Tuple> iterator() {
// some code goes here
return null;
}
}