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提交 6bed9021 authored 作者: Thomas Mueller's avatar Thomas Mueller
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LIRS replacement algorithm

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h2/src/test/org/h2/test/store/TestCache.java
浏览文件 @ 6bed9021
......@@ -10,7 +10,7 @@ import java.util.HashSet;
import java.util.List;
import java.util.Map.Entry;
import java.util.Random;
import org.h2.dev.store.btree.CacheLirs;
import org.h2.dev.store.btree.LIRSCache;
import org.h2.test.TestBase;
import org.h2.upgrade.v1_1.util.Profiler;
import org.h2.util.New;
......@@ -46,7 +46,7 @@ public class TestCache extends TestBase {
}
private void testEdgeCases() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(1, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(1, 1);
test.put(1, 10, 100);
assertEquals(10, test.get(1).intValue());
try {
......@@ -85,8 +85,8 @@ public class TestCache extends TestBase {
verifyMapSize(385, 1024);
verifyMapSize(769, 2048);
CacheLirs<Integer, Integer> test;
test = CacheLirs.newInstance(1000, 1);
LIRSCache<Integer, Integer> test;
test = LIRSCache.newInstance(1000, 1);
for (int j = 0; j < 2000; j++) {
test.put(j, j);
}
......@@ -99,17 +99,17 @@ public class TestCache extends TestBase {
}
private void verifyMapSize(int elements, int mapSize) {
CacheLirs<Integer, Integer> test;
test = CacheLirs.newInstance(elements - 1, 1);
LIRSCache<Integer, Integer> test;
test = LIRSCache.newInstance(elements - 1, 1);
assertTrue(mapSize > test.sizeMapArray());
test = CacheLirs.newInstance(elements, 1);
test = LIRSCache.newInstance(elements, 1);
assertEquals(mapSize, test.sizeMapArray());
test = CacheLirs.newInstance(elements * 100, 100);
test = LIRSCache.newInstance(elements * 100, 100);
assertEquals(mapSize, test.sizeMapArray());
}
private void testGetPutPeekRemove() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(4, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(4, 1);
test.put(1, 10);
test.put(2, 20);
test.put(3, 30);
......@@ -226,7 +226,7 @@ public class TestCache extends TestBase {
}
private void testPruneStack() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(5, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(5, 1);
for (int i = 0; i < 7; i++) {
test.put(i, i * 10);
}
......@@ -245,7 +245,7 @@ public class TestCache extends TestBase {
}
private void testClear() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(40, 10);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(40, 10);
for (int i = 0; i < 5; i++) {
test.put(i, 10 * i, 9);
}
......@@ -294,7 +294,7 @@ public class TestCache extends TestBase {
}
private void testLimitHot() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(100, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(100, 1);
for (int i = 0; i < 300; i++) {
test.put(i, 10 * i);
}
......@@ -304,7 +304,7 @@ public class TestCache extends TestBase {
}
private void testLimitNonResident() {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(4, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(4, 1);
for (int i = 0; i < 20; i++) {
test.put(i, 10 * i);
}
......@@ -339,7 +339,7 @@ public class TestCache extends TestBase {
}
CacheLirs<BadHash, Integer> test = CacheLirs.newInstance(size * 2, 1);
LIRSCache<BadHash, Integer> test = LIRSCache.newInstance(size * 2, 1);
for (int i = 0; i < size; i++) {
test.put(new BadHash(i), i);
}
......@@ -378,7 +378,7 @@ public class TestCache extends TestBase {
boolean log = false;
int size = 20;
// cache size 11 (10 hot, 1 cold)
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(size / 2 + 1, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(size / 2 + 1, 1);
// init the cache with some dummy entries
for (int i = 0; i < size; i++) {
test.put(-i, -i * 10);
......@@ -432,7 +432,7 @@ public class TestCache extends TestBase {
int size = 10;
Random r = new Random(1);
for (int j = 0; j < 100; j++) {
CacheLirs<Integer, Integer> test = CacheLirs.newInstance(size / 2, 1);
LIRSCache<Integer, Integer> test = LIRSCache.newInstance(size / 2, 1);
HashMap<Integer, Integer> good = New.hashMap();
for (int i = 0; i < 10000; i++) {
int key = r.nextInt(size);
......@@ -473,7 +473,7 @@ public class TestCache extends TestBase {
}
}
private static <K, V> String toString(CacheLirs<K, V> cache) {
private static <K, V> String toString(LIRSCache<K, V> cache) {
StringBuilder buff = new StringBuilder();
buff.append("mem: " + cache.getUsedMemory());
buff.append(" stack:");
......@@ -491,7 +491,7 @@ public class TestCache extends TestBase {
return buff.toString();
}
private <K, V> void verify(CacheLirs<K, V> cache, String expected) {
private <K, V> void verify(LIRSCache<K, V> cache, String expected) {
if (expected != null) {
String got = toString(cache);
assertEquals(expected, got);
......
h2/src/tools/org/h2/dev/store/btree/LIRSCache.java 0 → 100644
浏览文件 @ 6bed9021
/*
* Copyright 2004-2011 H2 Group. Multiple-Licensed under the H2 License,
* Version 1.0, and under the Eclipse Public License, Version 1.0
* (http://h2database.com/html/license.html).
* Initial Developer: H2 Group
*/
package org.h2.dev.store.btree;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.HashSet;
import java.util.List;
import java.util.Map;
import java.util.Set;
/**
* A scan resistent cache. It is meant to cache objects that are relatively
* costly to acquire, for example file content.
* <p>
* This implementation is not multi-threading save. Null keys or null values are
* not allowed. There is no guard against bad hash functions, so it is important
* to the hash function of the key is good. The map fill factor is at most 75%.
* <p>
* Each entry is assigned a distinct memory size, and the cache will try to use
* at most the specified amount of memory. The memory unit is not relevant,
* however it is suggested to use bytes as the unit.
* <p>
* This class implements the LIRS replacement algorithm invented by Xiaodong
* Zhang and Song Jiang as described in
* http://www.cse.ohio-state.edu/~zhang/lirs-sigmetrics-02.html with a few
* smaller changes: An additional queue for non-resident entries is used, to
* prevent unbound memory usage. The maximum size of this queue is at most the
* size of the rest of the stack. About 6.25% of the mapped entries are cold.
*
* @author Thomas Mueller
* @param <K> the key type
* @param <V> the value type
*/
public class LIRSCache<K, V> implements Map<K, V> {
/**
* The maximum memory this cache should use.
*/
private long maxMemory;
/**
* The average memory used by one entry.
*/
private int averageMemory;
/**
* The currently used memory.
*/
private long usedMemory;
/**
* The number of (hot, cold, and non-resident) entries in the map.
*/
private int mapSize;
/**
* The LIRS stack size.
*/
private int stackSize;
/**
* The size of the LIRS queue for resident cold entries.
*/
private int queueSize;
/**
* The size of the LIRS queue for non-resident cold entries.
*/
private int queue2Size;
/**
* The map array. The size is always a power of 2.
*/
private Entry<K, V>[] entries;
/**
* The bit mask that is applied to the key hash code to get the index in the
* map array. The mask is the length of the array minus one.
*/
private int mask;
/**
* The stack of recently referenced elements. This includes all hot entries,
* the recently referenced cold entries, and all non-resident cold entries.
*/
private Entry<K, V> stack;
/**
* The queue of resident cold entries.
*/
private Entry<K, V> queue;
/**
* The queue of non-resident cold entries.
*/
private Entry<K, V> queue2;
/**
* Create a new cache.
*
* @param maxMemory the maximum memory to use
* @param averageMemory the average memory usage of an object
*/
private LIRSCache(long maxMemory, int averageMemory) {
setMaxMemory(maxMemory);
setAverageMemory(averageMemory);
clear();
}
/**
* Create a new cache with the given memory size. To just limit the number
* of entries, use the required number as the maximum memory, and an average
* size of 1.
*
* @param maxMemory the maximum memory to use (1 or larger)
* @param averageMemory the average memory (1 or larger)
* @return the cache
*/
public static <K, V> LIRSCache<K, V> newInstance(int maxMemory, int averageMemory) {
return new LIRSCache<K, V>(maxMemory, averageMemory);
}
/**
* Clear the cache. This method will clear all entries (including
* non-resident keys) and resize the internal array.
**/
public void clear() {
// calculate the size of the map array
// assume a fill factor of at most 80%
long maxLen = (long) (maxMemory / averageMemory / 0.75);
// the size needs to be a power of 2
long l = 8;
while (l < maxLen) {
l += l;
}
// the array size is at most 2^31 elements
int len = (int) Math.min(1L << 31, l);
// the bit mask has all bits set
mask = len - 1;
// initialize the stack and queue heads
stack = new Entry<K, V>();
stack.stackPrev = stack.stackNext = stack;
queue = new Entry<K, V>();
queue.queuePrev = queue.queueNext = queue;
queue2 = new Entry<K, V>();
queue2.queuePrev = queue2.queueNext = queue2;
// first set to null - avoiding out of memory
entries = null;
@SuppressWarnings("unchecked")
Entry<K, V>[] e = new Entry[len];
entries = e;
mapSize = 0;
usedMemory = 0;
stackSize = queueSize = queue2Size = 0;
}
/**
* Get the value for the given key if the entry is cached. This method does
* not modify the internal state.
*
* @param key the key (may not be null)
* @return the value, or null if there is no resident entry
*/
public V peek(K key) {
Entry<K, V> e = find(key);
return e == null ? null : e.value;
}
/**
* Get the memory used for the given key.
*
* @param key the key (may not be null)
* @return the memory, or 0 if there is no resident entry
*/
public int getMemory(K key) {
Entry<K, V> e = find(key);
return e == null ? 0 : e.memory;
}
/**
* Get the value for the given key if the entry is cached. This method
* adjusts the internal state of the cache, to ensure commonly used entries
* stay in the cache.
*
* @param key the key (may not be null)
* @return the value, or null if there is no resident entry
*/
public V get(Object key) {
Entry<K, V> e = find(key);
if (e == null || e.value == null) {
// either the entry was not found, or it was a non-resident entry
return null;
} else if (e.isHot()) {
if (e != stack.stackNext) {
// move a hot entries to the top of the stack
// unless it is already there
boolean wasEnd = e == stack.stackPrev;
removeFromStack(e);
if (wasEnd) {
// if moving the last entry, the last entry
// could not be cold, which is not allowed
pruneStack();
}
addToStack(e);
}
} else {
removeFromQueue(e);
if (e.stackNext != null) {
// resident cold entries become hot
// if they are on the stack
removeFromStack(e);
// which means a hot entry needs to become cold
convertOldestHotToCold();
} else {
// cold entries that are not on the stack
// move to the front of the queue
addToQueue(queue, e);
}
// in any case, the cold entry is moved to the top of the stack
addToStack(e);
}
return e.value;
}
/**
* Add an entry to the cache using the average memory size.
*
* @param key the key (may not be null)
* @param value the value (may not be null)
*/
public V put(K key, V value) {
return put(key, value, averageMemory);
}
/**
* Add an entry to the cache. The entry may or may not exist in the cache
* yet. This method will usually mark unknown entries as cold and known
* entries as hot.
*
* @param key the key (may not be null)
* @param value the value (may not be null)
* @param memory the memory used for the given entry
*/
public V put(K key, V value, int memory) {
if (value == null) {
throw new NullPointerException();
}
V old;
Entry<K, V> e = find(key);
if (e == null) {
old = null;
} else {
old = e.value;
remove(key);
}
e = new Entry<K, V>();
e.key = key;
e.value = value;
e.memory = memory;
int index = key.hashCode() & mask;
e.mapNext = entries[index];
entries[index] = e;
usedMemory += memory;
if (usedMemory > maxMemory && mapSize > 0) {
// an old entry needs to be removed
evict(e);
}
mapSize++;
// added entries are always added to the stack
addToStack(e);
return old;
}
/**
* Remove an entry. Both resident and non-resident entries can be removed.
*
* @param key the key (may not be null)
* @return the old value, or null if there is no resident entry
*/
public V remove(Object key) {
int hash = key.hashCode();
int index = hash & mask;
Entry<K, V> e = entries[index];
if (e == null) {
return null;
}
V old;
if (e.key.equals(key)) {
old = e.value;
entries[index] = e.mapNext;
} else {
Entry<K, V> last;
do {
last = e;
e = e.mapNext;
if (e == null) {
return null;
}
} while (!e.key.equals(key));
old = e.value;
last.mapNext = e.mapNext;
}
mapSize--;
usedMemory -= e.memory;
if (e.stackNext != null) {
removeFromStack(e);
}
if (e.isHot()) {
// when removing a hot entry, the newest cold entry gets hot,
// so the number of hot entries does not change
e = queue.queueNext;
if (e != queue) {
removeFromQueue(e);
if (e.stackNext == null) {
addToStackBottom(e);
}
}
} else {
removeFromQueue(e);
}
pruneStack();
return old;
}
/**
* Evict cold entries (resident and non-resident) until the memory limit is
* reached.
*
* @param newCold a new cold entry
*/
private void evict(Entry<K, V> newCold) {
// ensure there are not too many hot entries:
// left shift of 5 is multiplication by 32, that means if there are less
// than 1/32 (3.125%) cold entries, a new hot entry needs to become cold
while ((queueSize << 5) < mapSize) {
convertOldestHotToCold();
}
// the new cold entry is at the top of the queue
addToQueue(queue, newCold);
// the oldest resident cold entries become non-resident
while (usedMemory > maxMemory) {
Entry<K, V> e = queue.queuePrev;
usedMemory -= e.memory;
removeFromQueue(e);
e.value = null;
e.memory = 0;
addToQueue(queue2, e);
// the size of the non-resident-cold entries needs to be limited
while (queue2Size + queue2Size > stackSize) {
e = queue2.queuePrev;
remove(e.key);
}
}
}
private void convertOldestHotToCold() {
// the last entry of the stack is known to be hot
Entry<K, V> last = stack.stackPrev;
// remove from stack - which is done anyway in the stack pruning, but we
// can do it here as well
removeFromStack(last);
// adding an entry to the queue will make it cold
addToQueue(queue, last);
pruneStack();
}
/**
* Ensure the last entry of the stack is cold.
*/
private void pruneStack() {
while (true) {
Entry<K, V> last = stack.stackPrev;
if (last == stack || last.isHot()) {
break;
}
// the cold entry is still in the queue
removeFromStack(last);
}
}
/**
* Try to find an entry in the map.
*
* @param key the key
* @return the entry (might be a non-resident)
*/
private Entry<K, V> find(Object key) {
int hash = key.hashCode();
Entry<K, V> e = entries[hash & mask];
while (e != null && !e.key.equals(key)) {
e = e.mapNext;
}
return e;
}
private void addToStack(Entry<K, V> e) {
e.stackPrev = stack;
e.stackNext = stack.stackNext;
e.stackNext.stackPrev = e;
stack.stackNext = e;
stackSize++;
}
private void addToStackBottom(Entry<K, V> e) {
e.stackNext = stack;
e.stackPrev = stack.stackPrev;
e.stackPrev.stackNext = e;
stack.stackPrev = e;
stackSize++;
}
private void removeFromStack(Entry<K, V> e) {
e.stackPrev.stackNext = e.stackNext;
e.stackNext.stackPrev = e.stackPrev;
e.stackPrev = e.stackNext = null;
stackSize--;
}
private void addToQueue(Entry<K, V> q, Entry<K, V> e) {
e.queuePrev = q;
e.queueNext = q.queueNext;
e.queueNext.queuePrev = e;
q.queueNext = e;
if (e.value != null) {
queueSize++;
} else {
queue2Size++;
}
}
private void removeFromQueue(Entry<K, V> e) {
e.queuePrev.queueNext = e.queueNext;
e.queueNext.queuePrev = e.queuePrev;
e.queuePrev = e.queueNext = null;
if (e.value != null) {
queueSize--;
} else {
queue2Size--;
}
}
/**
* Get the list of keys. This method allows to view the internal state of
* the cache.
*
* @param cold if true, only keys for the cold entries are returned
* @param nonResident true for non-resident entries
* @return the key list
*/
public List<K> keys(boolean cold, boolean nonResident) {
ArrayList<K> s = new ArrayList<K>();
if (cold) {
Entry<K, V> start = nonResident ? queue2 : queue;
for (Entry<K, V> e = start.queueNext; e != start; e = e.queueNext) {
s.add(e.key);
}
} else {
for (Entry<K, V> e = stack.stackNext; e != stack; e = e.stackNext) {
s.add(e.key);
}
}
return s;
}
/**
* Get the number of resident entries.
*
* @return the number of entries
*/
public int size() {
return mapSize - queue2Size;
}
/**
* Check whether there are any resident entries in the map.
*
* @return true if there are no keys
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Check whether there is a resident entry for the given key.
*
* @return true if there is a resident entry
*/
public boolean containsKey(Object key) {
Entry<K, V> e = find(key);
return e != null && e.value != null;
}
/**
* Check whether there are any keys for the given value.
*
* @return true if there is a key for this value
*/
public boolean containsValue(Object value) {
return values().contains(value);
}
/**
* Add all entries of the given map to this map. This method will use the
* average memory size.
*
* @param m the source map
*/
public void putAll(Map<? extends K, ? extends V> m) {
for (Map.Entry<? extends K, ? extends V> e : m.entrySet()) {
put(e.getKey(), e.getValue());
}
}
/**
* Get the set of keys for resident entries.
*
* @return the set of keys
*/
public Set<K> keySet() {
HashSet<K> set = new HashSet<K>();
for (Entry<K, V> e = stack.stackNext; e != stack; e = e.stackNext) {
set.add(e.key);
}
for (Entry<K, V> e = queue.queueNext; e != queue; e = e.queueNext) {
set.add(e.key);
}
return set;
}
/**
* Get the collection of values.
*
* @return the collection of values
*/
public Collection<V> values() {
ArrayList<V> list = new ArrayList<V>();
for (K k : keySet()) {
list.add(get(k));
}
return list;
}
/**
* Get the entry set for all resident entries.
*
* @return the entry set
*/
public Set<Map.Entry<K, V>> entrySet() {
HashMap<K, V> map = new HashMap<K, V>();
for (K k : keySet()) {
map.put(k, find(k).value);
}
return map.entrySet();
}
/**
* Get the number of hot entries in the cache.
*
* @return the number of hot entries
*/
public int sizeHot() {
return mapSize - queueSize - queue2Size;
}
/**
* Get the number of non-resident entries in the cache.
*
* @return the number of non-resident entries
*/
public int sizeNonResident() {
return queue2Size;
}
/**
* Get the length of the internal map array.
*
* @return the size of the array
*/
public int sizeMapArray() {
return entries.length;
}
/**
* Get the currently used memory.
*
* @return the used memory
*/
public long getUsedMemory() {
return usedMemory;
}
/**
* Set the maximum memory this cache should use. This will not immediately
* cause entries to get removed however; it will only change the limit. To
* resize the internal array, call the clear method.
*
* @param maxMemory the maximum size (1 or larger)
*/
public void setMaxMemory(long maxMemory) {
if (maxMemory <= 0) {
throw new IllegalArgumentException("Max memory must be larger than 0");
}
this.maxMemory = maxMemory;
}
/**
* Get the maximum memory to use.
*
* @return the maximum memory
*/
public long getMaxMemory() {
return maxMemory;
}
/**
* Set the average memory used per entry. It is used to calculate the length
* of the internal array.
*
* @param averageMemory the average memory used (1 or larger)
*/
public void setAverageMemory(int averageMemory) {
if (averageMemory <= 0) {
throw new IllegalArgumentException("Average memory must be larger than 0");
}
this.averageMemory = averageMemory;
}
/**
* Get the average memory used per entry.
*
* @return the average memory
*/
public int getAverageMemory() {
return averageMemory;
}
/**
* A cache entry. Each entry is either hot (low inter-reference recency;
* LIR), cold (high inter-reference recency; HIR), or non-resident-cold. Hot
* entries are in the stack only. Cold entries are in the queue, and may be
* in the stack. Non-resident-cold entries have their value set to null and
* are in the stack and in the non-resident queue.
*
* @param <K> the key type
* @param <V> the value type
*/
static class Entry<K, V> {
/**
* The key.
*/
K key;
/**
* The value. Set to null for non-resident-cold entries.
*/
V value;
/**
* The estimated memory used.
*/
int memory;
/**
* The next entry in the stack.
*/
Entry<K, V> stackNext;
/**
* The previous entry in the stack.
*/
Entry<K, V> stackPrev;
/**
* The next entry in the queue (either the resident queue or the
* non-resident queue).
*/
Entry<K, V> queueNext;
/**
* The previous entry in the queue.
*/
Entry<K, V> queuePrev;
/**
* The next entry in the map
*/
Entry<K, V> mapNext;
/**
* Whether this entry is hot. Cold entries are in one of the two queues.
*
* @return whether the entry is hot
*/
boolean isHot() {
return queueNext == null;
}
}
}
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