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本文次要钻研一下claudb的Database
Database
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/Database.java
public interface Database { int size(); boolean isEmpty(); boolean containsKey(DatabaseKey key); DatabaseValue get(DatabaseKey key); DatabaseValue put(DatabaseKey key, DatabaseValue value); DatabaseValue remove(DatabaseKey key); void clear(); ImmutableSet<DatabaseKey> keySet(); Sequence<DatabaseValue> values(); ImmutableSet<Tuple2<DatabaseKey, DatabaseValue>> entrySet(); default SafeString getString(SafeString key) { return getOrDefault(safeKey(key), DatabaseValue.EMPTY_STRING).getString(); } default ImmutableList<SafeString> getList(SafeString key) { return getOrDefault(safeKey(key), DatabaseValue.EMPTY_LIST).getList(); } default ImmutableSet<SafeString> getSet(SafeString key) { return getOrDefault(safeKey(key), DatabaseValue.EMPTY_SET).getSet(); } default NavigableSet<Entry<Double, SafeString>> getSortedSet(SafeString key) { return getOrDefault(safeKey(key), DatabaseValue.EMPTY_ZSET).getSortedSet(); } default ImmutableMap<SafeString, SafeString> getHash(SafeString key) { return getOrDefault(safeKey(key), DatabaseValue.EMPTY_HASH).getHash(); } default void putAll(ImmutableMap<? extends DatabaseKey, ? extends DatabaseValue> map) { map.forEach(this::put); } default DatabaseValue putIfAbsent(DatabaseKey key, DatabaseValue value) { DatabaseValue oldValue = get(key); if (oldValue == null) { oldValue = put(key, value); } return oldValue; } default DatabaseValue merge(DatabaseKey key, DatabaseValue value, BiFunction<DatabaseValue, DatabaseValue, DatabaseValue> remappingFunction) { DatabaseValue oldValue = get(key); DatabaseValue newValue = oldValue == null ? value : remappingFunction.apply(oldValue, value); if(newValue == null) { remove(key); } else { put(key, newValue); } return newValue; } default DatabaseValue getOrDefault(DatabaseKey key, DatabaseValue defaultValue) { DatabaseValue value = get(key); return (value != null || containsKey(key)) ? value : defaultValue; } default boolean isType(DatabaseKey key, DataType type) { DatabaseValue value = get(key); return value != null ? value.getType() == type : true; } default boolean rename(DatabaseKey from, DatabaseKey to) { DatabaseValue value = remove(from); if (value != null) { put(to, value); return true; } return false; } default void overrideAll(ImmutableMap<DatabaseKey, DatabaseValue> value) { clear(); putAll(value); } default ImmutableSet<DatabaseKey> evictableKeys(Instant now) { return entrySet() .filter(entry -> entry.get2().isExpired(now)) .map(Tuple2::get1); }}- Database接口定义了size、isEmpty、containsKey、get、put、remove、clear、keySet、values、entrySet办法；同时还提供了getString、getList、getSet、getSortedSet、getHash、putAll、putIfAbsent、merge、getOrDefault、isType、rename、overrideAll、evictableKeys这几个default办法
OnHeapDatabase
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/OnHeapDatabase.java
public class OnHeapDatabase implements Database { private final Map<DatabaseKey, DatabaseValue> cache; public OnHeapDatabase(Map<DatabaseKey, DatabaseValue> cache) { this.cache = cache; } @Override public int size() { return cache.size(); } @Override public boolean isEmpty() { return cache.isEmpty(); } @Override public boolean containsKey(DatabaseKey key) { return cache.containsKey(key); } @Override public DatabaseValue get(DatabaseKey key) { DatabaseValue value = cache.get(key); if (value != null) { if (!value.isExpired(Instant.now())) { return value; } cache.remove(key); } return null; } @Override public DatabaseValue put(DatabaseKey key, DatabaseValue value) { DatabaseValue oldValue = cache.remove(key); cache.put(key, value); return oldValue; } @Override public DatabaseValue remove(DatabaseKey key) { return cache.remove(key); } @Override public void clear() { cache.clear(); } @Override public ImmutableSet<DatabaseKey> keySet() { return ImmutableSet.from(cache.keySet()); } @Override public Sequence<DatabaseValue> values() { return ImmutableSet.from(cache.values()); } @Override public ImmutableSet<Tuple2<DatabaseKey, DatabaseValue>> entrySet() { return ImmutableSet.from(cache.entrySet()).map(Tuple::from); }}- OnHeapDatabase实现了Database接口，它应用Map构造作为cache；其get办法在取出value不为null时会判断该value是否过期，如果过期则移除该key，返回null；其put办法会先执行remove获取oldValue，在put进去新值，最初返回oldValue
OffHeapDatabase
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/OffHeapDatabase.java
public class OffHeapDatabase implements Database { private OHCache<DatabaseKey, DatabaseValue> cache; public OffHeapDatabase(OHCache<DatabaseKey, DatabaseValue> cache) { this.cache = cache; } @Override public int size() { return (int) cache.size(); } @Override public boolean isEmpty() { return cache.size() == 0; } @Override public boolean containsKey(DatabaseKey key) { return cache.containsKey(key); } @Override public DatabaseValue get(DatabaseKey key) { DatabaseValue value = cache.get(key); if (value != null) { if (!value.isExpired(Instant.now())) { return value; } cache.remove(key); } return null; } @Override public DatabaseValue put(DatabaseKey key, DatabaseValue value) { cache.put(key, value); return value; } @Override public DatabaseValue remove(DatabaseKey key) { DatabaseValue value = get(key); cache.remove(key); return value; } @Override public void clear() { cache.clear(); } @Override public ImmutableSet<DatabaseKey> keySet() { Set<DatabaseKey> keys = new HashSet<>(); try (CloseableIterator<DatabaseKey> iterator = cache.keyIterator()) { while (iterator.hasNext()) { keys.add(iterator.next()); } } catch(IOException e) { throw new UncheckedIOException(e); } return ImmutableSet.from(keys); } @Override public Sequence<DatabaseValue> values() { List<DatabaseValue> values = new LinkedList<>(); for (DatabaseKey key : keySet()) { values.add(cache.get(key)); } return ImmutableList.from(values); } @Override public ImmutableSet<Tuple2<DatabaseKey, DatabaseValue>> entrySet() { return keySet().map(key -> Tuple.of(key, get(key))); }}- OffHeapDatabase实现了Database接口，它应用OHCache作为cache，其get办法在取出value不为null时会判断该value是否过期，如果过期则移除该key，返回null；其put办法间接往cache笼罩该key，返回的是新值
DatabaseFactory
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/DatabaseFactory.java
public interface DatabaseFactory { Database create(String name); void clear();}- DatabaseFactory接口定义了create、clear办法
OnHeapDatabaseFactory
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/OnHeapDatabaseFactory.java
public class OnHeapDatabaseFactory implements DatabaseFactory { @Override public Database create(String name) { return new OnHeapDatabase(new HashMap<>()); } @Override public void clear() { // nothing to clear }}- OnHeapDatabaseFactory实现了DatabaseFactory接口，其create应用HashMap创立OnHeapDatabase
OffHeapDatabaseFactory
claudb-1.7.1/src/main/java/com/github/tonivade/claudb/data/OffHeapDatabaseFactory.java
public class OffHeapDatabaseFactory implements DatabaseFactory { @Override public Database create(String name) { return new OffHeapDatabase(createCache()); } private OHCache<DatabaseKey, DatabaseValue> createCache() { return builder() .eviction(Eviction.NONE) .throwOOME(true) .keySerializer(new FSTSerializer<>()) .valueSerializer(new FSTSerializer<>()) .build(); } private OHCacheBuilder<DatabaseKey, DatabaseValue> builder() { return OHCacheBuilder.newBuilder(); } @Override public void clear() { // nothing to do } private static class FSTSerializer<E> implements CacheSerializer<E> { private static final FSTConfiguration FST = FSTConfiguration.createDefaultConfiguration(); static { FST.registerClass(DatabaseValue.class); FST.registerClass(DatabaseKey.class); FST.registerClass(SafeString.class); FST.registerClass(SortedSet.class); } @Override public void serialize(E value, ByteBuffer buf) { byte[] array = FST.asByteArray(value); buf.putInt(array.length); buf.put(array); } @SuppressWarnings("unchecked") @Override public E deserialize(ByteBuffer buf) { int length = buf.getInt(); byte[] array = new byte[length]; buf.get(array); return (E) FST.asObject(array); } @Override public int serializedSize(E value) { return FST.asByteArray(value).length + Integer.BYTES; } }}- OffHeapDatabaseFactory实现了DatabaseFactory接口，其create办法创立的是OffHeapDatabase；其createCache办法应用OHCacheBuilder来结构OHCache，其eviction为NONE，其throwOOME为true；其keySerializer及valueSerializer均为FSTSerializer
小结
claudb提供了OnHeapDatabase、OffHeapDatabase两种实现，前者应用HashMap，后者应用OHCache
doc
- Database