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Segment Space-Efficient Index (#3533)
This patch replaces the Segment's ConcurrentHashMap index to a more space-efficient index. Memory overhead is reduced from 943120 to 80856 bytes, ~11x.
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infrastructure/src/main/java/org/corfudb/infrastructure/log/BoundedMap.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,106 @@ | ||
| package org.corfudb.infrastructure.log; | ||
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| import com.google.common.base.Preconditions; | ||
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| import java.util.Iterator; | ||
| import java.util.concurrent.atomic.AtomicLongArray; | ||
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| /** | ||
| * A BoundedMap provides an array backed map that can map long -> long where the indices are in the range of | ||
| * (Long.MIN_VALUE, Long.MAX_VALUE - Integer.MAX_VALUE) | ||
| */ | ||
| public class BoundedMap { | ||
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| private final long offset; | ||
| private final AtomicLongArray array; | ||
| public static final long NOT_SET = Long.MIN_VALUE; | ||
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| public BoundedMap(long offset, int size) { | ||
| Preconditions.checkArgument(offset >= 0); | ||
| Preconditions.checkArgument(size > 0); | ||
| Preconditions.checkArgument(Math.addExact(offset, size) < Integer.MAX_VALUE); | ||
| this.offset = offset; | ||
| this.array = new AtomicLongArray(size); | ||
| for (int idx = 0; idx < array.length(); idx++) { | ||
| this.array.set(idx, NOT_SET); | ||
| } | ||
| } | ||
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| private void checkRange(long num) { | ||
| if (num < offset || num >= offset + array.length()) { | ||
| throw new IllegalArgumentException(num + " not in [" + offset + ", " + (offset + array.length()) + ")"); | ||
| } | ||
| } | ||
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| private void checkValue(long value) { | ||
| Preconditions.checkArgument(NOT_SET != value, "invalid %s value", value); | ||
| } | ||
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| private int mapIdx(long idx) { | ||
| return Math.toIntExact(idx - offset); | ||
| } | ||
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| public boolean set(long idx, long value) { | ||
| checkRange(idx); | ||
| checkValue(value); | ||
| return array.compareAndSet(mapIdx(idx), NOT_SET, value); | ||
| } | ||
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| public long get(long idx) { | ||
| checkRange(idx); | ||
| return array.get(mapIdx(idx)); | ||
| } | ||
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| public boolean contains(long idx) { | ||
| checkRange(idx); | ||
| return array.get(mapIdx(idx)) != NOT_SET; | ||
| } | ||
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| public int capacity() { | ||
| return array.length(); | ||
| } | ||
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| /** | ||
| * Iterators are only used for initialization and therefore are not optimized. For instance, the running time | ||
| * for iterating is not a function of the number of elements set in the index, but rather the size of the index. | ||
| */ | ||
| public Iterator<Long> iterator() { | ||
| return new IndexIterator(array); | ||
| } | ||
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| public Iterable<Long> iterable() { | ||
| final Iterator<Long> iter = iterator(); | ||
| return () -> iter; | ||
| } | ||
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| private final class IndexIterator implements Iterator<Long> { | ||
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| private final AtomicLongArray array; | ||
| private int idx = 0; | ||
| private IndexIterator(AtomicLongArray array) { | ||
| this.array = array; | ||
| findNextIdx(); | ||
| } | ||
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| private void findNextIdx() { | ||
| while (idx < array.length() && array.get(idx) == NOT_SET) { | ||
| idx++; | ||
| } | ||
| } | ||
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| @Override | ||
| public boolean hasNext() { | ||
| return idx < array.length(); | ||
| } | ||
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| @Override | ||
| public Long next() { | ||
| long ret = array.get(idx); | ||
| Preconditions.checkState(ret != NOT_SET); | ||
| long retVal = idx + offset; | ||
| idx++; | ||
| findNextIdx(); | ||
| return retVal; | ||
| } | ||
| } | ||
| } |
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