recoverymgr.java

用java语言简单实现数据库的初步功能

package simpledb.tx.recovery;

import static simpledb.tx.recovery.LogRecord.*;
import simpledb.file.Block;
import simpledb.buffer.Buffer;
import simpledb.server.SimpleDB;
import java.util.*;

/**
 * The recovery manager.  Each transaction has its own recovery manager.
 * @author Edward Sciore
 */
public class RecoveryMgr {
	private int txnum;

	/**
	 * Creates a recovery manager for the specified transaction.
	 * @param txnum the ID of the specified transaction
	 */
	public RecoveryMgr(int txnum) {
		this.txnum = txnum;
		new StartRecord(txnum).writeToLog();
	}

	/**
	 * Writes a commit record to the log, and flushes it to disk.
	 */
	public void commit() {
		SimpleDB.bufferMgr().flushAll(txnum);
		int lsn = new CommitRecord(txnum).writeToLog();
		SimpleDB.logMgr().flush(lsn);
	}

	/**
	 * Writes a rollback record to the log, and flushes it to disk.
	 */
	public void rollback() {
		SimpleDB.bufferMgr().flushAll(txnum);
		doRollback();
		int lsn = new RollbackRecord(txnum).writeToLog();
		SimpleDB.logMgr().flush(lsn);
	}

	/**
	 * Recovers uncompleted transactions from the log,
	 * then writes a quiescent checkpoint record to the log and flushes it.
	 */
	public void recover() {
		doRecover();
		int lsn = new CheckpointRecord().writeToLog();
		SimpleDB.logMgr().flush(lsn);

	}

	/**
	 * Writes a setint record to the log, and returns its lsn.
	 * Updates to temporary files are not logged; instead, a
	 * "dummy" lsn of -1 is returned.
	 * @param buff the buffer containing the page
	 * @param offset the offset of the value in the page
	 * @param newval the value to be written
	 */
	public int setInt(Buffer buff, int offset, int newval) {
		int oldval = buff.getInt(offset);
		Block blk = buff.block();
		if (isTempBlock(blk))
			return -1;
		else
			return new SetIntRecord(txnum, blk, offset, oldval).writeToLog();
	}

	/**
	 * Writes a setstring record to the log, and returns its lsn.
	 * Updates to temporary files are not logged; instead, a
	 * "dummy" lsn of -1 is returned.
	 * @param buff the buffer containing the page
	 * @param offset the offset of the value in the page
	 * @param newval the value to be written
	 */
	public int setString(Buffer buff, int offset, String newval) {
		String oldval = buff.getString(offset);
		Block blk = buff.block();
		if (isTempBlock(blk))
			return -1;
		else
			return new SetStringRecord(txnum, blk, offset, oldval).writeToLog();
	}

	/**
	 * Rolls back the transaction.
	 * The method iterates through the log records,
	 * calling undo() for each log record it finds
	 * for the transaction,
	 * until it finds the transaction's START record.
	 */
	private void doRollback() {
		Iterator<LogRecord> iter = new LogRecordIterator();
		while (iter.hasNext()) {
			LogRecord rec = iter.next();
			if (rec.txNumber() == txnum) {
				if (rec.op() == START)
					return;
				rec.undo(txnum);
			}
		}
	}

	/**
	 * Does a complete database recovery.
	 * The method iterates through the log records.
	 * Whenever it finds a log record for an uncommitted
	 * transaction, it calls undo() on that record.
	 * The method stops when it encounters a CHECKPOINT record
	 * or the end of the log.
	 */
	private void doRecover() {
		Collection<Integer> committedTxs = new ArrayList<Integer>();
		Iterator<LogRecord> iter = new LogRecordIterator();
		while (iter.hasNext()) {
			LogRecord rec = iter.next();
			if (rec.op() == CHECKPOINT)
				return;
			if (rec.op() == COMMIT)
				committedTxs.add(rec.txNumber());
			else if (!committedTxs.contains(rec.txNumber()))
				rec.undo(txnum);
		}
	}

	/**
	 * Determines whether a block comes from a temporary file or not.
	 */
	private boolean isTempBlock(Block blk) {
		return blk.fileName().startsWith("temp");
	}
}