/**
* 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);
}
public void clear() {
lru.clear();
fifo.clear();
recentlyUsed.clear();
lastUsed = -1;
}
public CacheObject find(int pos) {
CacheObject r = lru.find(pos);
if (r == null) {
r = fifo.find(pos);
}
return r;
}
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;
}
public ArrayList<CacheObject> getAllChanged() {
ArrayList<CacheObject> changed = New.arrayList();
changed.addAll(lru.getAllChanged());
changed.addAll(fifo.getAllChanged());
return changed;
}
public int getMaxMemory() {
return maxMemory;
}
public int getMemory() {
return lru.getMemory() + fifo.getMemory();
}
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();
}
}
public boolean remove(int pos) {
boolean result = lru.remove(pos);
if (!result) {
result = fifo.remove(pos);
}
recentlyUsed.remove(pos);
return result;
}
public void setMaxMemory(int maxMemoryKb) {
this.maxMemory = maxMemoryKb;
lru.setMaxMemory((int) (maxMemoryKb * 0.8));
fifo.setMaxMemory((int) (maxMemoryKb * 0.2));
recentlyUsed.setMaxSize(4 * maxMemoryKb);
}
public CacheObject update(int pos, CacheObject record) {
if (lru.find(pos) != null) {
return lru.update(pos, record);
}
return fifo.update(pos, record);
}
}
