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提交 1bf1dde3 authored 作者: Thomas Mueller's avatar Thomas Mueller
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The LIRS cache now re-sizes the internal hash map if needed.

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h2/src/docsrc/html/changelog.html
浏览文件 @ 1bf1dde3
......@@ -17,6 +17,8 @@ Change Log
<h1>Change Log</h1>
<h2>Next Version (unreleased)</h2>
<ul><li>The LIRS cache now re-sizes the internal hash map if needed.
</li></ul>
<h2>Version 1.4.179 Beta (2014-06-23)</h2>
<ul><li>The license was changed to MPL 2.0 (from 1.0) and EPL 1.0.
......
h2/src/main/org/h2/mvstore/cache/CacheLongKeyLIRS.java
浏览文件 @ 1bf1dde3
......@@ -93,8 +93,8 @@ public class CacheLongKeyLIRS<V> {
this.stackMoveDistance = stackMoveDistance;
segments = new Segment[segmentCount];
clear();
this.segmentShift = Integer.numberOfTrailingZeros(
segments[0].entries.length);
// use the high bits for the segment
this.segmentShift = 32 - Integer.bitCount(segmentMask);
}
/**
......@@ -102,12 +102,26 @@ public class CacheLongKeyLIRS<V> {
*/
public void clear() {
long max = Math.max(1, maxMemory / segmentCount);
int segmentLen = getSegmentLen(max);
for (int i = 0; i < segmentCount; i++) {
segments[i] = new Segment<V>(
max, averageMemory, stackMoveDistance);
max, segmentLen, stackMoveDistance);
}
}
private int getSegmentLen(long max) {
// calculate the size of the map array
// assume a fill factor of at most 75%
long maxLen = (long) (max / 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
return (int) Math.min(1L << 31, l);
}
private Entry<V> find(long key) {
int hash = getHash(key);
return getSegment(hash).find(key, hash);
......@@ -160,7 +174,23 @@ public class CacheLongKeyLIRS<V> {
*/
public V put(long key, V value, int memory) {
int hash = getHash(key);
return getSegment(hash).put(key, hash, value, memory);
int segmentIndex = getSegmentIndex(hash);
Segment<V> s = segments[segmentIndex];
// check whether resize is required:
// synchronize on s, to avoid concurrent writes also
// resize (concurrent reads read from the old segment)
synchronized (s) {
if (s.isFull()) {
// another thread might have resized
// (as we retrieved the segment before synchronizing on it)
s = segments[segmentIndex];
if (s.isFull()) {
s = new Segment<V>(s, 2);
segments[segmentIndex] = s;
}
}
return s.put(key, hash, value, memory);
}
}
/**
......@@ -211,8 +241,11 @@ public class CacheLongKeyLIRS<V> {
}
private Segment<V> getSegment(int hash) {
int segmentIndex = (hash >>> segmentShift) & segmentMask;
return segments[segmentIndex];
return segments[getSegmentIndex(hash)];
}
private int getSegmentIndex(int hash) {
return (hash >>> segmentShift) & segmentMask;
}
/**
......@@ -276,11 +309,6 @@ public class CacheLongKeyLIRS<V> {
averageMemory > 0,
"Average memory must be larger than 0, is {0}", averageMemory);
this.averageMemory = averageMemory;
if (segments != null) {
for (Segment<V> s : segments) {
s.setAverageMemory(averageMemory);
}
}
}
/**
......@@ -483,7 +511,7 @@ public class CacheLongKeyLIRS<V> {
/**
* The map array. The size is always a power of 2.
*/
Entry<V>[] entries;
final Entry<V>[] entries;
/**
* The currently used memory.
......@@ -501,11 +529,6 @@ public class CacheLongKeyLIRS<V> {
*/
private long maxMemory;
/**
* The average memory used by one entry.
*/
private int averageMemory;
/**
* 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.
......@@ -546,32 +569,17 @@ public class CacheLongKeyLIRS<V> {
private int stackMoveCounter;
/**
* Create a new cache.
* Create a new cache segment.
*
* @param maxMemory the maximum memory to use
* @param averageMemory the average memory usage of an object
* @param len the number of hash table buckets (must be a power of 2)
* @param stackMoveDistance the number of other entries to be moved to
* the top of the stack before moving an entry to the top
*/
Segment(long maxMemory, int averageMemory, int stackMoveDistance) {
Segment(long maxMemory, int len, int stackMoveDistance) {
setMaxMemory(maxMemory);
setAverageMemory(averageMemory);
this.stackMoveDistance = stackMoveDistance;
clear();
}
private 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;
......@@ -583,8 +591,6 @@ public class CacheLongKeyLIRS<V> {
queue2 = new Entry<V>();
queue2.queuePrev = queue2.queueNext = queue2;
// first set to null - avoiding out of memory
entries = null;
@SuppressWarnings("unchecked")
Entry<V>[] e = new Entry[len];
entries = e;
......@@ -594,6 +600,74 @@ public class CacheLongKeyLIRS<V> {
stackSize = queueSize = queue2Size = 0;
}
/**
* Create a new, larger cache segment from an existing one.
* The caller must synchronize on the old segment, to avoid
* concurrent modifications.
*
* @param old the old segment
* @param resizeFactor the factor to use to calculate the number of hash
* table buckets (must be a power of 2)
*/
Segment(Segment<V> old, int resizeFactor) {
this(old.maxMemory,
old.entries.length * resizeFactor,
old.stackMoveDistance);
Entry<V> s = old.stack.stackPrev;
while (s != old.stack) {
Entry<V> e = copy(s);
addToMap(e);
addToStack(e);
s = s.stackPrev;
}
s = old.queue.queuePrev;
while (s != old.queue) {
Entry<V> e = find(s.key, getHash(s.key));
if (e == null) {
e = copy(s);
addToMap(e);
}
addToQueue(queue, e);
s = s.queuePrev;
}
s = old.queue2.queuePrev;
while (s != old.queue2) {
Entry<V> e = find(s.key, getHash(s.key));
if (e == null) {
e = copy(s);
addToMap(e);
}
addToQueue(queue2, e);
s = s.queuePrev;
}
}
private void addToMap(Entry<V> e) {
int index = getHash(e.key) & mask;
e.mapNext = entries[index];
entries[index] = e;
usedMemory += e.memory;
mapSize++;
}
private static <V> Entry<V> copy(Entry<V> old) {
Entry<V> e = new Entry<V>();
e.key = old.key;
e.value = old.value;
e.memory = old.memory;
e.topMove = old.topMove;
return e;
}
/**
* Check whether the cache segment is full.
*
* @return true if it contains more entries than hash table buckets.
*/
public boolean isFull() {
return mapSize > mask;
}
/**
* Get the memory used for the given key.
*
......@@ -982,16 +1056,6 @@ public class CacheLongKeyLIRS<V> {
this.maxMemory = 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)
*/
void setAverageMemory(int averageMemory) {
this.averageMemory = averageMemory;
}
}
/**
......@@ -1047,7 +1111,7 @@ public class CacheLongKeyLIRS<V> {
Entry<V> queuePrev;
/**
* The next entry in the map
* The next entry in the map (the chained entry).
*/
Entry<V> mapNext;
......
h2/src/test/org/h2/test/store/TestCacheLongKeyLIRS.java
浏览文件 @ 1bf1dde3
......@@ -34,6 +34,7 @@ public class TestCacheLongKeyLIRS extends TestBase {
}
private void testCache() {
testResize();
testRandomSmallCache();
testEdgeCases();
testSize();
......@@ -46,6 +47,21 @@ public class TestCacheLongKeyLIRS extends TestBase {
testRandomOperations();
}
private void testResize() {
// cache with 100 memory, average memory 10
// (that means 10 entries)
CacheLongKeyLIRS<Integer> t1 =
new CacheLongKeyLIRS<Integer>(100, 10, 1, 0);
// another cache with more entries
CacheLongKeyLIRS<Integer> t2 =
new CacheLongKeyLIRS<Integer>(100, 1, 1, 0);
for (int i = 0; i < 200; i++) {
t1.put(i, i, 1);
t2.put(i, i, 1);
}
assertEquals(toString(t2), toString(t1));
}
private static void testRandomSmallCache() {
Random r = new Random(1);
for (int i = 0; i < 10000; i++) {
......
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