[Paged File, I/O System] 초코칩(권기호) 미션 제출합니다. (#3)

* feat: 페이지 구조 구현

* feat: 페이지 직렬화

* feat: 페이지 팩터리 패턴 적용

* feat: 페이지 매니저 생성

* test: DisplayName 수정

* feat: 불필요 PageManager 삭제

* feat: 버퍼풀 구현

* refactor: innodb 패키지 생성

* feat: 더티 상태 구현

* feat: 페이지 내의 레코드 기능 구현

* feat: 페이지 디렉터리 구현

* feat: 레코드 추가 기능 구현

* feat: 레코드 변경 시, 더티 체크

* feat: 테이블 별로 페이지 저장

* feat: 페이지 번호 반환

* refactor: 버퍼풀 패키지 생성

* feat: 페이지 교체 알고리즘 전략 패턴 적용

* refactor: 포트에 final 적용

* refactor: 코드 포멧팅

* feat: 핸들러 삽입 구현

* refactor: 레코드 파일 분리

* refactor: 패키지명 변경

* feat: 레코드 자료형 변경

* refactor: pageManager 버퍼풀 내로 이동

* refactor: 페이지 키 객체화

* refactor: key 변경

* refactor: filemanager로 클래스명 변경

* refactor: 개행 추가

* refactor(FileHeader): 불필요 체크섬 필드 제거

* refactor(FileExtension): 파일 확장자 분리

* refactor: 예외처리 구분

* refactor: 테스트 수정

src/main/java/database/Application.java

@@ -1,5 +1,7 @@
 package database;
 
+import database.engine.DatabaseServer;
+
 public class Application {
 
     public static void main(String[] args) {

src/main/java/database/ClientHandler.java → src/main/java/database/engine/ClientHandler.java

@@ -1,4 +1,4 @@
-package database;
+package database.engine;
 
 import java.io.BufferedReader;
 import java.io.InputStreamReader;
@@ -7,6 +7,7 @@
 import java.net.Socket;
 
 public class ClientHandler implements Runnable {
+
     private final Socket clientSocket;
 
     public ClientHandler(Socket clientSocket) {

src/main/java/database/DatabaseServer.java → src/main/java/database/engine/DatabaseServer.java

@@ -1,11 +1,12 @@
-package database;
+package database.engine;
 
 import java.io.IOException;
 import java.net.ServerSocket;
 import java.net.Socket;
 
 public class DatabaseServer {
-    private int port;
+
+    private final int port;
     private boolean isRunning;
 
     public DatabaseServer(int port) {

src/main/java/database/engine/Handler.java

@@ -0,0 +1,15 @@
+package database.engine;
+
+import java.util.List;
+
+public interface Handler {
+
+    void insert(String tableName, Record record);
+
+    List<Record> search(String tableName, Object key);
+
+    void update(String tableName, Object key, byte[] newRecord);
+
+    void delete(String tableName, Object key);
+}
+

src/main/java/database/engine/Record.java

@@ -0,0 +1,23 @@
+package database.engine;
+
+import java.util.List;
+
+public class Record {
+
+    private final List<Object> values;
+
+    public Record(List<Object> values) {
+        this.values = values;
+    }
+
+    public List<Object> getValues() {
+        return values;
+    }
+
+    @Override
+    public String toString() {
+        return "Record{" +
+                "values=" + values +
+                '}';
+    }
+}

src/main/java/database/storageEngine/StorageEngineHandler.java

@@ -0,0 +1,65 @@
+package database.storageEngine;
+
+import database.engine.Handler;
+import database.engine.Record;
+import database.storageEngine.bufferpool.BufferPool;
+import database.storageEngine.bufferpool.PageReplacementStrategy;
+import database.storageEngine.bufferpool.TablePageKey;
+import database.storageEngine.bufferpool.pageReplacementStrategies.LRUStrategy;
+import database.storageEngine.page.Page;
+import database.storageEngine.page.StorageRecord;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+public class StorageEngineHandler implements Handler {
+
+    private static final int BUFFER_SIZE = 40;
+
+    private final BufferPool bufferPool;
+
+    public StorageEngineHandler() {
+        PageReplacementStrategy<TablePageKey> lruStrategy = new LRUStrategy<>(BUFFER_SIZE);
+        this.bufferPool = new BufferPool(BUFFER_SIZE, lruStrategy);
+    }
+
+    @Override
+    public void insert(String tableName, Record record) {
+        StorageRecord storageRecord = new StorageRecord(record.getValues());
+        Page page = bufferPool.findPageWithSpace(tableName, storageRecord);
+        page.addRecord(storageRecord);
+    }
+
+    @Override
+    public List<Record> search(String tableName, Object key) {
+        List<Record> results = new ArrayList<>();
+
+        for (long pageNumber = 0; ; pageNumber++) {
+            TablePageKey tablePageKey = new TablePageKey(tableName, pageNumber);
+            Optional<Page> pageOpt = bufferPool.getPage(tablePageKey);
+
+            if (pageOpt.isPresent()) {
+                Page page = pageOpt.get();
+                List<Record> records = page.searchRecords(key).stream()
+                        .map(storageRecord -> new Record(storageRecord.getValues()))
+                        .toList();
+                if (!records.isEmpty()) {
+                    results.addAll(records);
+                }
+            } else {
+                break;
+            }
+        }
+        return results;
+    }
+
+    @Override
+    public void update(String tableName, Object key, byte[] newRecord) {
+        // 디스크에서 레코드를 업데이트하는 로직
+    }
+
+    @Override
+    public void delete(String tableName, Object key) {
+        // 디스크에서 레코드를 삭제하는 로직
+    }
+}

src/main/java/database/storageEngine/bufferpool/BufferPool.java

@@ -0,0 +1,87 @@
+package database.storageEngine.bufferpool;
+
+import database.storageEngine.page.FileExtension;
+import database.storageEngine.page.FileManager;
+import database.storageEngine.page.Page;
+import database.storageEngine.page.StorageRecord;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Optional;
+import java.util.stream.IntStream;
+
+public class BufferPool {
+
+    private final int capacity;
+    private final PageReplacementStrategy<TablePageKey> strategy;
+    private final Map<TablePageKey, Page> pages;
+    private final FileManager fileManager;
+
+    public BufferPool(int capacity, PageReplacementStrategy<TablePageKey> strategy) {
+        this.capacity = capacity;
+        this.strategy = strategy;
+        this.pages = new HashMap<>();
+        this.fileManager = new FileManager(FileExtension.IDB);
+    }
+
+    public Optional<Page> getPage(TablePageKey key) {
+        // Cache hit
+        if (pages.containsKey(key)) {
+            strategy.get(key);
+            return Optional.of(pages.get(key));
+        }
+
+        // Cache miss
+        Page page = fileManager.loadPage(key);
+        putPage(key, page);
+        return Optional.of(page);
+    }
+
+    public void putPage(TablePageKey key, Page page) {
+        if (!pages.containsKey(key)) {
+            if (pages.size() >= capacity) {
+                TablePageKey evictedKey = strategy.evict();
+                if (evictedKey != null) {
+                    flushPage(evictedKey);
+                    pages.remove(evictedKey);
+                }
+            }
+            pages.put(key, page);
+            strategy.put(key);
+        }
+    }
+
+    public void flushPage(TablePageKey key) {
+        if (pages.containsKey(key)) {
+            Page page = pages.get(key);
+            if (page.isDirty()) {
+                fileManager.savePage(key.tableName(), page);
+                page.clean();
+            }
+        }
+    }
+
+    public void flushAllPages() {
+        for (Map.Entry<TablePageKey, Page> entry : pages.entrySet()) {
+            flushPage(entry.getKey());
+        }
+    }
+
+    public void removePage(TablePageKey key) {
+        if (pages.containsKey(key)) {
+            flushPage(key);
+            pages.remove(key);
+            strategy.evict();
+        }
+    }
+
+    public Page findPageWithSpace(String tableName, StorageRecord storageRecord) {
+        return IntStream.range(0, capacity)
+                .mapToObj(pageNumber -> {
+                    TablePageKey key = new TablePageKey(tableName, pageNumber);
+                    return pages.get(key);
+                })
+                .filter(page -> page.getFreeSpace() >= storageRecord.getSize())
+                .findFirst()
+                .orElseGet(fileManager::createNewDataPage);
+    }
+}

src/main/java/database/storageEngine/bufferpool/PageReplacementStrategy.java

@@ -0,0 +1,14 @@
+package database.storageEngine.bufferpool;
+
+import java.util.Optional;
+
+public interface PageReplacementStrategy<K> {
+
+    Optional<K> get(K key);
+
+    void put(K key);
+
+    K evict();
+
+    boolean contains(K key);
+}

src/main/java/database/storageEngine/bufferpool/TablePageKey.java

@@ -0,0 +1,5 @@
+package database.storageEngine.bufferpool;
+
+public record TablePageKey(String tableName, long pageNumber) {
+
+}

src/main/java/database/storageEngine/bufferpool/pageReplacementStrategies/LFUStrategy.java

@@ -0,0 +1,66 @@
+package database.storageEngine.bufferpool.pageReplacementStrategies;
+
+import database.storageEngine.bufferpool.PageReplacementStrategy;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Optional;
+
+public class LFUStrategy<K> implements PageReplacementStrategy<K> {
+
+    private final int capacity;
+    private final Map<K, Integer> usageCount;
+    private final Map<K, Long> cache;
+
+    public LFUStrategy(int capacity) {
+        this.capacity = capacity;
+        this.usageCount = new HashMap<>();
+        this.cache = new HashMap<>();
+    }
+
+    @Override
+    public void put(K key) {
+        if (cache.size() >= capacity) {
+            evict();
+        }
+        cache.put(key, System.nanoTime()); // 현재 시간으로 타임스탬프 저장
+        usageCount.put(key, usageCount.getOrDefault(key, 0) + 1);
+    }
+
+    @Override
+    public K evict() {
+        K leastUsedKey = findLeastUsedKey();
+        if (leastUsedKey != null) {
+            cache.remove(leastUsedKey);
+            usageCount.remove(leastUsedKey);
+        }
+        return leastUsedKey;
+    }
+
+    @Override
+    public boolean contains(K key) {
+        return cache.containsKey(key);
+    }
+
+    private K findLeastUsedKey() {
+        Optional<Entry<K, Integer>> minEntry = usageCount.entrySet().stream()
+                .min((entry1, entry2) -> {
+                    int freqCompare = entry1.getValue().compareTo(entry2.getValue());
+                    if (freqCompare == 0) {
+                        // 동일한 사용 빈도일 경우, 먼저 들어온 키를 우선 제거
+                        return cache.get(entry1.getKey()).compareTo(cache.get(entry2.getKey()));
+                    }
+                    return freqCompare;
+                });
+        return minEntry.map(Map.Entry::getKey).orElse(null);
+    }
+
+    @Override
+    public Optional<K> get(K key) {
+        if (cache.containsKey(key)) {
+            usageCount.put(key, usageCount.get(key) + 1);
+            return Optional.of(key);
+        }
+        return Optional.empty();
+    }
+}

src/main/java/database/storageEngine/bufferpool/pageReplacementStrategies/LRUStrategy.java

@@ -0,0 +1,49 @@
+package database.storageEngine.bufferpool.pageReplacementStrategies;
+
+import database.storageEngine.bufferpool.PageReplacementStrategy;
+import java.util.LinkedHashSet;
+import java.util.Optional;
+
+public class LRUStrategy<K> implements PageReplacementStrategy<K> {
+
+    private final int capacity;
+    private final LinkedHashSet<K> cache;
+
+    public LRUStrategy(int capacity) {
+        this.capacity = capacity;
+        this.cache = new LinkedHashSet<>(capacity);
+    }
+
+    @Override
+    public void put(K key) {
+        if (cache.contains(key)) {
+            cache.remove(key);
+        } else if (cache.size() >= capacity) {
+            evict();
+        }
+        cache.add(key);
+    }
+
+    @Override
+    public K evict() {
+        K firstKey = cache.iterator().next();
+        cache.remove(firstKey);
+        return firstKey;
+    }
+
+    @Override
+    public boolean contains(K key) {
+        return cache.contains(key);
+    }
+
+    @Override
+    public Optional<K> get(K key) {
+        if (cache.contains(key)) {
+            cache.remove(key);
+            cache.add(key);
+            return Optional.of(key);
+        }
+        return Optional.empty();
+    }
+}
+