/*
* Copyright 2004-2023 H2 Group. Multiple-Licensed under the MPL 2.0,
* and the EPL 1.0 (https://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.util;
import java.util.ArrayList;
/**
* An alternative cache implementation. This implementation uses two caches: a
* LRU cache and a FIFO cache. Entries are first kept in the FIFO cache, and if
* referenced again then marked in a hash set. If referenced again, they are
* moved to the LRU cache. Stream pages are never added to the LRU cache. It is
* supposed to be more or less scan resistant, and it doesn't cache large rows
* in the LRU cache.
*/
public class CacheTQ implements Cache {
static final String TYPE_NAME = "TQ";
private final Cache lru;
private final Cache fifo;
private final SmallLRUCache<Integer, Object> recentlyUsed =
SmallLRUCache.newInstance(1024);
private int lastUsed = -1;
private int maxMemory;
CacheTQ(CacheWriter writer, int maxMemoryKb) {
this.maxMemory = maxMemoryKb;
lru = new CacheLRU(writer, (int) (maxMemoryKb * 0.8), false);
fifo = new CacheLRU(writer, (int) (maxMemoryKb * 0.2), true);
setMaxMemory(4 * maxMemoryKb);
}
@Override
public void clear() {
lru.clear();
fifo.clear();
recentlyUsed.clear();
lastUsed = -1;
}
@Override
public CacheObject find(int pos) {
CacheObject r = lru.find(pos);
if (r == null) {
r = fifo.find(pos);
}
return r;
}
@Override
public CacheObject get(int pos) {
CacheObject r = lru.find(pos);
if (r != null) {
return r;
}
r = fifo.find(pos);
if (r != null && !r.isStream()) {
if (recentlyUsed.get(pos) != null) {
if (lastUsed != pos) {
fifo.remove(pos);
lru.put(r);
}
} else {
recentlyUsed.put(pos, this);
}
lastUsed = pos;
}
return r;
}
@Override
public ArrayList<CacheObject> getAllChanged() {
ArrayList<CacheObject> lruChanged = lru.getAllChanged();
ArrayList<CacheObject> fifoChanged = fifo.getAllChanged();
ArrayList<CacheObject> changed = new ArrayList<>(lruChanged.size() + fifoChanged.size());
changed.addAll(lruChanged);
changed.addAll(fifoChanged);
return changed;
}
@Override
public int getMaxMemory() {
return maxMemory;
}
@Override
public int getMemory() {
return lru.getMemory() + fifo.getMemory();
}
@Override
public void put(CacheObject r) {
if (r.isStream()) {
fifo.put(r);
} else if (recentlyUsed.get(r.getPos()) != null) {
lru.put(r);
} else {
fifo.put(r);
lastUsed = r.getPos();
}
}
@Override
public boolean remove(int pos) {
boolean result = lru.remove(pos);
if (!result) {
result = fifo.remove(pos);
}
recentlyUsed.remove(pos);
return result;
}
@Override
public void setMaxMemory(int maxMemoryKb) {
this.maxMemory = maxMemoryKb;
lru.setMaxMemory((int) (maxMemoryKb * 0.8));
fifo.setMaxMemory((int) (maxMemoryKb * 0.2));
recentlyUsed.setMaxSize(4 * maxMemoryKb);
}
@Override
public CacheObject update(int pos, CacheObject record) {
if (lru.find(pos) != null) {
return lru.update(pos, record);
}
return fifo.update(pos, record);
}
}