160 lines
5.0 KiB
Java
160 lines
5.0 KiB
Java
import org.jetbrains.annotations.Contract;
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import java.io.FileWriter;
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import java.io.IOException;
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import java.util.*;
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/**
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* Persistence manager using the Singleton pattern.
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*/
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public class PersistenceManager {
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private final static PersistenceManager instance;
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private Hashtable<Integer, String> _pageBuffer;
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private Hashtable<Integer, Set<Integer>> _transactionPageBuffer;
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private Hashtable<Integer, Boolean> _transactions;
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private Hashtable<Integer, Integer> _pageLSN;
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private int _nextTransactionNumber;
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private int _nextLogSequenceNumber;
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static {
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try {
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instance = new PersistenceManager();
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} catch (Throwable e) {
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throw new RuntimeException(e.getMessage());
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}
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}
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/**
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* Returns an instance of the persistence manager.
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*
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* @return instance
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*/
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@Contract(pure = true)
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public static PersistenceManager getInstance() {
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return instance;
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}
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/**
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* private constructor
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*/
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private PersistenceManager() {
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_pageBuffer = new Hashtable<>();
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_transactionPageBuffer = new Hashtable<>();
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_transactions = new Hashtable<>();
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_pageLSN = new Hashtable<>();
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_nextTransactionNumber = 1;
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_nextLogSequenceNumber = 1;
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}
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/**
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* Begins the transaction and returns the transaction ID.
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*
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* @return transaction ID
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*/
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public int beginTransaction() {
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_transactions.put(_nextTransactionNumber, false);
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// return the next transaction number and increase it by one afterwards
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return _nextTransactionNumber++;
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}
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/**
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* Commits the transaction specified by given ID.
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*
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* @param taid
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* transaction ID
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*/
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public void commit(int taid) {
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if (!_transactions.containsKey(taid)) {
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throw new IllegalArgumentException("No transaction with given ID exists.");
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}
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// only perform commit actions if transaction isn't commited yet
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if (!_transactions.get(taid)) {
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_transactions.replace(taid, true);
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}
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}
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/**
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* Writes given data into given page in given transaction.
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*
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* @param taid
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* transaction ID
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* @param pageid
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* page ID
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* @param data
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* data
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*/
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public void write(int taid, int pageid, String data) {
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if (!_transactions.containsKey(taid)) {
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throw new IllegalArgumentException("No transaction with given ID exists.");
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}
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if (_transactions.get(taid)) {
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throw new IllegalArgumentException("Write operations cannot be performed for committed transactions.");
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}
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Set<Integer> pageIDs = _transactionPageBuffer.getOrDefault(taid, new HashSet<>());
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pageIDs.add(pageid);
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_transactionPageBuffer.put(taid, pageIDs);
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_pageBuffer.put(pageid, data);
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// log changes
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int lsn = log(taid, pageid, data);
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_pageLSN.put(pageid, lsn);
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// call persist
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persist();
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}
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/**
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* Logs the necessary information to the log file.
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*
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* @param taid
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* affected transaction
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* @param pageid
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* modified page
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* @param data
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* written data
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* @return log sequence number
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*/
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private int log(int taid, int pageid, String data) {
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try {
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FileWriter fw = new FileWriter("../data/log.txt", true);
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// TODO properly create redo data
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fw.write("" + _nextLogSequenceNumber + "," + taid + "," + pageid + "," + data);
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fw.write("\n");
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fw.close();
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} catch (IOException e) {
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e.printStackTrace();
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}
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return _nextLogSequenceNumber++;
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}
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/**
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* Checks for full buffer and persists data of committed transactions to storage if buffer is full.
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*/
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private void persist() {
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if (_pageBuffer.size() <= 5) {
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return;
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}
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// TODO persist the data of committed transactions
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Enumeration<Integer> transactionIDs = _transactions.keys();
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List<Integer> commitedTransactions = new ArrayList<>();
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while (transactionIDs.hasMoreElements()) {
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Integer taid = transactionIDs.nextElement();
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boolean committed = _transactions.get(taid);
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if (committed) {
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commitedTransactions.add(taid);
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}
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}
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for (int taid : commitedTransactions) {
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// TODO persist data of committed transaction
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Set<Integer> pageIDs = _transactionPageBuffer.get(taid);
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for (int pageid : pageIDs) {
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// TODO persist data of pageID
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_pageBuffer.remove(pageid);
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}
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_transactionPageBuffer.remove(taid);
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_transactions.remove(taid);
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}
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}
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}
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