Java tutorial
/*********************************************************************************************************************** * Copyright (C) 2010-2013 by the Stratosphere project (http://stratosphere.eu) * * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the * specific language governing permissions and limitations under the License. **********************************************************************************************************************/ package eu.stratosphere.pact.runtime.hash; import java.io.EOFException; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.concurrent.atomic.AtomicBoolean; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import eu.stratosphere.api.common.typeutils.TypeComparator; import eu.stratosphere.api.common.typeutils.TypePairComparator; import eu.stratosphere.api.common.typeutils.TypeSerializer; import eu.stratosphere.core.memory.MemorySegment; import eu.stratosphere.nephele.services.memorymanager.ListMemorySegmentSource; import eu.stratosphere.pact.runtime.util.MathUtils; import eu.stratosphere.util.MutableObjectIterator; /** * An implementation of an in-memory Hash Table for variable-length records. * <p> * The design of this class follows on many parts the design presented in * "Hash joins and hash teams in Microsoft SQL Server", by Goetz Graefe et al.. *<p> * * * <hr> * * The layout of the buckets inside a memory segment is as follows: * * <pre> * +----------------------------- Bucket x ---------------------------- * |Partition (1 byte) | Status (1 byte) | element count (2 bytes) | * | next-bucket-in-chain-pointer (8 bytes) | reserved (4 bytes) | * | * |hashCode 1 (4 bytes) | hashCode 2 (4 bytes) | hashCode 3 (4 bytes) | * | ... hashCode n-1 (4 bytes) | hashCode n (4 bytes) * | * |pointer 1 (8 bytes) | pointer 2 (8 bytes) | pointer 3 (8 bytes) | * | ... pointer n-1 (8 bytes) | pointer n (8 bytes) * | * +---------------------------- Bucket x + 1-------------------------- * |Partition (1 byte) | Status (1 byte) | element count (2 bytes) | * | next-bucket-in-chain-pointer (8 bytes) | reserved (4 bytes) | * | * |hashCode 1 (4 bytes) | hashCode 2 (4 bytes) | hashCode 3 (4 bytes) | * | ... hashCode n-1 (4 bytes) | hashCode n (4 bytes) * | * |pointer 1 (8 bytes) | pointer 2 (8 bytes) | pointer 3 (8 bytes) | * | ... pointer n-1 (8 bytes) | pointer n (8 bytes) * +------------------------------------------------------------------- * | ... * | * </pre> * @param <T> * * @param T record type stored in hash table * */ public class CompactingHashTable<T> extends AbstractMutableHashTable<T> { private static final Log LOG = LogFactory.getLog(CompactingHashTable.class); // ------------------------------------------------------------------------ // Internal Constants // ------------------------------------------------------------------------ private static final int MIN_NUM_MEMORY_SEGMENTS = 33; /** * The maximum number of partitions */ private static final int MAX_NUM_PARTITIONS = 32; /** * The default record width that is used when no width is given. The record width is * used to determine the ratio of the number of memory segments intended for partition * buffers and the number of memory segments in the hash-table structure. */ private static final int DEFAULT_RECORD_LEN = 24; //FIXME maybe find a better default /** * The length of the hash code stored in the bucket. */ private static final int HASH_CODE_LEN = 4; /** * The length of a pointer from a hash bucket to the record in the buffers. */ private static final int POINTER_LEN = 8; /** * The number of bytes that the entry in the hash structure occupies, in bytes. * It corresponds to a 4 byte hash value and an 8 byte pointer. */ private static final int RECORD_TABLE_BYTES = HASH_CODE_LEN + POINTER_LEN; /** * The total storage overhead per record, in bytes. This corresponds to the space in the * actual hash table buckets, consisting of a 4 byte hash value and an 8 byte * pointer, plus the overhead for the stored length field. */ private static final int RECORD_OVERHEAD_BYTES = RECORD_TABLE_BYTES; // -------------------------- Bucket Size and Structure ------------------------------------- private static final int NUM_INTRA_BUCKET_BITS = 7; private static final int HASH_BUCKET_SIZE = 0x1 << NUM_INTRA_BUCKET_BITS; private static final int BUCKET_HEADER_LENGTH = 16; private static final int NUM_ENTRIES_PER_BUCKET = (HASH_BUCKET_SIZE - BUCKET_HEADER_LENGTH) / RECORD_OVERHEAD_BYTES; private static final int BUCKET_POINTER_START_OFFSET = BUCKET_HEADER_LENGTH + (NUM_ENTRIES_PER_BUCKET * HASH_CODE_LEN); // ------------------------------ Bucket Header Fields ------------------------------ /** * Offset of the field in the bucket header indicating the bucket's partition. */ private static final int HEADER_PARTITION_OFFSET = 0; /** * Offset of the field in the bucket header indicating the bucket's status (spilled or in-memory). */ private static final int HEADER_COUNT_OFFSET = 4; /** * Offset of the field in the bucket header that holds the forward pointer to its * first overflow bucket. */ private static final int HEADER_FORWARD_OFFSET = 8; /** * Constant for the forward pointer, indicating that the pointer is not set. */ private static final long BUCKET_FORWARD_POINTER_NOT_SET = ~0x0L; // ------------------------------------------------------------------------ // Members // ------------------------------------------------------------------------ /** * The free memory segments currently available to the hash join. */ private final ArrayList<MemorySegment> availableMemory; /** * The size of the segments used by the hash join buckets. All segments must be of equal size to ease offset computations. */ private final int segmentSize; /** * The number of hash table buckets in a single memory segment - 1. * Because memory segments can be comparatively large, we fit multiple buckets into one memory segment. * This variable is a mask that is 1 in the lower bits that define the number of a bucket * in a segment. */ private final int bucketsPerSegmentMask; /** * The number of bits that describe the position of a bucket in a memory segment. Computed as log2(bucketsPerSegment). */ private final int bucketsPerSegmentBits; /** * An estimate for the average record length. */ private final int avgRecordLen; // ------------------------------------------------------------------------ /** * The partitions of the hash table. */ private final ArrayList<InMemoryPartition<T>> partitions; /** * The array of memory segments that contain the buckets which form the actual hash-table * of hash-codes and pointers to the elements. */ private MemorySegment[] buckets; /** * temporary storage for partition compaction (always attempts to allocate as many segments as the largest partition) */ private InMemoryPartition<T> compactionMemory; /** * The number of buckets in the current table. The bucket array is not necessarily fully * used, when not all buckets that would fit into the last segment are actually used. */ private int numBuckets; private AtomicBoolean closed = new AtomicBoolean(); private boolean running = true; private int pageSizeInBits; // ------------------------------------------------------------------------ // Construction and Teardown // ------------------------------------------------------------------------ public CompactingHashTable(TypeSerializer<T> buildSideSerializer, TypeComparator<T> buildSideComparator, List<MemorySegment> memorySegments) { this(buildSideSerializer, buildSideComparator, memorySegments, DEFAULT_RECORD_LEN); } public CompactingHashTable(TypeSerializer<T> buildSideSerializer, TypeComparator<T> buildSideComparator, List<MemorySegment> memorySegments, int avgRecordLen) { super(buildSideSerializer, buildSideComparator); // some sanity checks first if (memorySegments == null) { throw new NullPointerException(); } if (memorySegments.size() < MIN_NUM_MEMORY_SEGMENTS) { throw new IllegalArgumentException("Too few memory segments provided. Hash Join needs at least " + MIN_NUM_MEMORY_SEGMENTS + " memory segments."); } this.availableMemory = (memorySegments instanceof ArrayList) ? (ArrayList<MemorySegment>) memorySegments : new ArrayList<MemorySegment>(memorySegments); this.avgRecordLen = buildSideSerializer.getLength() > 0 ? buildSideSerializer.getLength() : avgRecordLen; // check the size of the first buffer and record it. all further buffers must have the same size. // the size must also be a power of 2 this.segmentSize = memorySegments.get(0).size(); if ((this.segmentSize & this.segmentSize - 1) != 0) { throw new IllegalArgumentException("Hash Table requires buffers whose size is a power of 2."); } int bucketsPerSegment = this.segmentSize >> NUM_INTRA_BUCKET_BITS; if (bucketsPerSegment == 0) { throw new IllegalArgumentException( "Hash Table requires buffers of at least " + HASH_BUCKET_SIZE + " bytes."); } this.bucketsPerSegmentMask = bucketsPerSegment - 1; this.bucketsPerSegmentBits = MathUtils.log2strict(bucketsPerSegment); this.partitions = new ArrayList<InMemoryPartition<T>>(); // because we allow to open and close multiple times, the state is initially closed this.closed.set(true); // so far no partition has any MemorySegments } // ------------------------------------------------------------------------ // Life-Cycle // ------------------------------------------------------------------------ /** * Build the hash table * * @throws IOException Thrown, if an I/O problem occurs while spilling a partition. */ public void open() { // sanity checks if (!this.closed.compareAndSet(true, false)) { throw new IllegalStateException("Hash Table cannot be opened, because it is currently not closed."); } // create the partitions final int partitionFanOut = getPartitioningFanOutNoEstimates(this.availableMemory.size()); createPartitions(partitionFanOut); // set up the table structure. the write behind buffers are taken away, as are one buffer per partition final int numBuckets = getInitialTableSize(this.availableMemory.size(), this.segmentSize, partitionFanOut, this.avgRecordLen); initTable(numBuckets, (byte) partitionFanOut); } /** * Closes the hash table. This effectively releases all internal structures and closes all * open files and removes them. The call to this method is valid both as a cleanup after the * complete inputs were properly processed, and as an cancellation call, which cleans up * all resources that are currently held by the hash join. */ public void close() { // make sure that we close only once if (!this.closed.compareAndSet(false, true)) { return; } LOG.debug("Closing hash table and releasing resources."); // release the table structure releaseTable(); // clear the memory in the partitions clearPartitions(); } public void abort() { this.running = false; LOG.debug("Cancelling hash table operations."); } public List<MemorySegment> getFreeMemory() { if (!this.closed.get()) { throw new IllegalStateException("Cannot return memory while join is open."); } return this.availableMemory; } public void buildTable(final MutableObjectIterator<T> input) throws IOException { T record = this.buildSideSerializer.createInstance(); // go over the complete input and insert every element into the hash table while (this.running && ((record = input.next(record)) != null)) { insert(record); } } public final void insert(T record) throws IOException { final int hashCode = hash(this.buildSideComparator.hash(record)); final int posHashCode = hashCode % this.numBuckets; // get the bucket for the given hash code final int bucketArrayPos = posHashCode >>> this.bucketsPerSegmentBits; final int bucketInSegmentPos = (posHashCode & this.bucketsPerSegmentMask) << NUM_INTRA_BUCKET_BITS; final MemorySegment bucket = this.buckets[bucketArrayPos]; // get the basic characteristics of the bucket final int partitionNumber = bucket.get(bucketInSegmentPos + HEADER_PARTITION_OFFSET); final InMemoryPartition<T> p = this.partitions.get(partitionNumber); long pointer; try { pointer = p.appendRecord(record); if ((pointer >> this.pageSizeInBits) > this.compactionMemory.getBlockCount()) { this.compactionMemory.allocateSegments((int) (pointer >> this.pageSizeInBits)); } } catch (EOFException e) { try { compactPartition(partitionNumber); // retry append pointer = this.partitions.get(partitionNumber).appendRecord(record); } catch (EOFException ex) { throw new RuntimeException( "Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } catch (IndexOutOfBoundsException ex) { throw new RuntimeException( "Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } } catch (IndexOutOfBoundsException e1) { try { compactPartition(partitionNumber); // retry append pointer = this.partitions.get(partitionNumber).appendRecord(record); } catch (EOFException ex) { throw new RuntimeException( "Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } catch (IndexOutOfBoundsException ex) { throw new RuntimeException( "Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } } insertBucketEntryFromStart(p, bucket, bucketInSegmentPos, hashCode, pointer); } @Override public <PT> HashTableProber<PT> getProber(TypeComparator<PT> probeSideComparator, TypePairComparator<PT, T> pairComparator) { return new HashTableProber<PT>(probeSideComparator, pairComparator); } /** * * @return Iterator over hash table * @see EntryIterator */ public MutableObjectIterator<T> getEntryIterator() { return new EntryIterator(this); } /** * Replaces record in hash table if record already present or append record if not. * May trigger expensive compaction. * * @param record record to insert or replace * @param tempHolder instance of T that will be overwritten * @throws IOException */ public void insertOrReplaceRecord(T record, T tempHolder) throws IOException { final int searchHashCode = hash(this.buildSideComparator.hash(record)); final int posHashCode = searchHashCode % this.numBuckets; // get the bucket for the given hash code MemorySegment originalBucket = this.buckets[posHashCode >> this.bucketsPerSegmentBits]; int originalBucketOffset = (posHashCode & this.bucketsPerSegmentMask) << NUM_INTRA_BUCKET_BITS; MemorySegment bucket = originalBucket; int bucketInSegmentOffset = originalBucketOffset; // get the basic characteristics of the bucket final int partitionNumber = bucket.get(bucketInSegmentOffset + HEADER_PARTITION_OFFSET); final InMemoryPartition<T> partition = this.partitions.get(partitionNumber); final MemorySegment[] overflowSegments = partition.overflowSegments; this.buildSideComparator.setReference(record); int countInSegment = bucket.getInt(bucketInSegmentOffset + HEADER_COUNT_OFFSET); int numInSegment = 0; int posInSegment = bucketInSegmentOffset + BUCKET_HEADER_LENGTH; long currentForwardPointer = BUCKET_FORWARD_POINTER_NOT_SET; // loop over all segments that are involved in the bucket (original bucket plus overflow buckets) while (true) { while (numInSegment < countInSegment) { final int thisCode = bucket.getInt(posInSegment); posInSegment += HASH_CODE_LEN; // check if the hash code matches if (thisCode == searchHashCode) { // get the pointer to the pair final int pointerOffset = bucketInSegmentOffset + BUCKET_POINTER_START_OFFSET + (numInSegment * POINTER_LEN); final long pointer = bucket.getLong(pointerOffset); numInSegment++; // deserialize the key to check whether it is really equal, or whether we had only a hash collision try { partition.readRecordAt(pointer, tempHolder); if (this.buildSideComparator.equalToReference(tempHolder)) { long newPointer = partition.appendRecord(record); bucket.putLong(pointerOffset, newPointer); partition.setCompaction(false); if ((newPointer >> this.pageSizeInBits) > this.compactionMemory.getBlockCount()) { this.compactionMemory.allocateSegments((int) (newPointer >> this.pageSizeInBits)); } return; } } catch (EOFException e) { // system is out of memory so we attempt to reclaim memory with a copy compact run long newPointer; try { compactPartition(partition.getPartitionNumber()); // retry append newPointer = this.partitions.get(partitionNumber).appendRecord(record); } catch (EOFException ex) { throw new RuntimeException("Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } catch (IndexOutOfBoundsException ex) { throw new RuntimeException("Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } bucket.putLong(pointerOffset, newPointer); return; } catch (IndexOutOfBoundsException e) { // system is out of memory so we attempt to reclaim memory with a copy compact run long newPointer; try { compactPartition(partition.getPartitionNumber()); // retry append newPointer = this.partitions.get(partitionNumber).appendRecord(record); } catch (EOFException ex) { throw new RuntimeException("Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } catch (IndexOutOfBoundsException ex) { throw new RuntimeException("Memory ran out. Compaction failed. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length + " Message: " + ex.getMessage()); } bucket.putLong(pointerOffset, newPointer); return; } catch (IOException e) { throw new RuntimeException( "Error deserializing record from the hashtable: " + e.getMessage(), e); } } else { numInSegment++; } } // this segment is done. check if there is another chained bucket long newForwardPointer = bucket.getLong(bucketInSegmentOffset + HEADER_FORWARD_OFFSET); if (newForwardPointer == BUCKET_FORWARD_POINTER_NOT_SET) { // nothing found. append and insert long pointer = partition.appendRecord(record); insertBucketEntryFromSearch(partition, originalBucket, bucket, originalBucketOffset, bucketInSegmentOffset, countInSegment, currentForwardPointer, searchHashCode, pointer); if ((pointer >> this.pageSizeInBits) > this.compactionMemory.getBlockCount()) { this.compactionMemory.allocateSegments((int) (pointer >> this.pageSizeInBits)); } return; } final int overflowSegNum = (int) (newForwardPointer >>> 32); bucket = overflowSegments[overflowSegNum]; bucketInSegmentOffset = (int) (newForwardPointer & 0xffffffff); countInSegment = bucket.getInt(bucketInSegmentOffset + HEADER_COUNT_OFFSET); posInSegment = bucketInSegmentOffset + BUCKET_HEADER_LENGTH; numInSegment = 0; currentForwardPointer = newForwardPointer; } } private final void insertBucketEntryFromStart(InMemoryPartition<T> p, MemorySegment bucket, int bucketInSegmentPos, int hashCode, long pointer) throws IOException { // find the position to put the hash code and pointer final int count = bucket.getInt(bucketInSegmentPos + HEADER_COUNT_OFFSET); if (count < NUM_ENTRIES_PER_BUCKET) { // we are good in our current bucket, put the values bucket.putInt(bucketInSegmentPos + BUCKET_HEADER_LENGTH + (count * HASH_CODE_LEN), hashCode); // hash code bucket.putLong(bucketInSegmentPos + BUCKET_POINTER_START_OFFSET + (count * POINTER_LEN), pointer); // pointer bucket.putInt(bucketInSegmentPos + HEADER_COUNT_OFFSET, count + 1); // update count } else { // we need to go to the overflow buckets final long originalForwardPointer = bucket.getLong(bucketInSegmentPos + HEADER_FORWARD_OFFSET); final long forwardForNewBucket; if (originalForwardPointer != BUCKET_FORWARD_POINTER_NOT_SET) { // forward pointer set final int overflowSegNum = (int) (originalForwardPointer >>> 32); final int segOffset = (int) (originalForwardPointer & 0xffffffff); final MemorySegment seg = p.overflowSegments[overflowSegNum]; final int obCount = seg.getInt(segOffset + HEADER_COUNT_OFFSET); // check if there is space in this overflow bucket if (obCount < NUM_ENTRIES_PER_BUCKET) { // space in this bucket and we are done seg.putInt(segOffset + BUCKET_HEADER_LENGTH + (obCount * HASH_CODE_LEN), hashCode); // hash code seg.putLong(segOffset + BUCKET_POINTER_START_OFFSET + (obCount * POINTER_LEN), pointer); // pointer seg.putInt(segOffset + HEADER_COUNT_OFFSET, obCount + 1); // update count return; } else { // no space here, we need a new bucket. this current overflow bucket will be the // target of the new overflow bucket forwardForNewBucket = originalForwardPointer; } } else { // no overflow bucket yet, so we need a first one forwardForNewBucket = BUCKET_FORWARD_POINTER_NOT_SET; } // we need a new overflow bucket MemorySegment overflowSeg; final int overflowBucketNum; final int overflowBucketOffset; // first, see if there is space for an overflow bucket remaining in the last overflow segment if (p.nextOverflowBucket == 0) { // no space left in last bucket, or no bucket yet, so create an overflow segment overflowSeg = getNextBuffer(); overflowBucketOffset = 0; overflowBucketNum = p.numOverflowSegments; // add the new overflow segment if (p.overflowSegments.length <= p.numOverflowSegments) { MemorySegment[] newSegsArray = new MemorySegment[p.overflowSegments.length * 2]; System.arraycopy(p.overflowSegments, 0, newSegsArray, 0, p.overflowSegments.length); p.overflowSegments = newSegsArray; } p.overflowSegments[p.numOverflowSegments] = overflowSeg; p.numOverflowSegments++; } else { // there is space in the last overflow bucket overflowBucketNum = p.numOverflowSegments - 1; overflowSeg = p.overflowSegments[overflowBucketNum]; overflowBucketOffset = p.nextOverflowBucket << NUM_INTRA_BUCKET_BITS; } // next overflow bucket is one ahead. if the segment is full, the next will be at the beginning // of a new segment p.nextOverflowBucket = (p.nextOverflowBucket == this.bucketsPerSegmentMask ? 0 : p.nextOverflowBucket + 1); // insert the new overflow bucket in the chain of buckets // 1) set the old forward pointer // 2) let the bucket in the main table point to this one overflowSeg.putLong(overflowBucketOffset + HEADER_FORWARD_OFFSET, forwardForNewBucket); final long pointerToNewBucket = (((long) overflowBucketNum) << 32) | ((long) overflowBucketOffset); bucket.putLong(bucketInSegmentPos + HEADER_FORWARD_OFFSET, pointerToNewBucket); // finally, insert the values into the overflow buckets overflowSeg.putInt(overflowBucketOffset + BUCKET_HEADER_LENGTH, hashCode); // hash code overflowSeg.putLong(overflowBucketOffset + BUCKET_POINTER_START_OFFSET, pointer); // pointer // set the count to one overflowSeg.putInt(overflowBucketOffset + HEADER_COUNT_OFFSET, 1); } } private final void insertBucketEntryFromSearch(InMemoryPartition<T> partition, MemorySegment originalBucket, MemorySegment currentBucket, int originalBucketOffset, int currentBucketOffset, int countInCurrentBucket, long currentForwardPointer, int hashCode, long pointer) { if (countInCurrentBucket < NUM_ENTRIES_PER_BUCKET) { // we are good in our current bucket, put the values currentBucket.putInt( currentBucketOffset + BUCKET_HEADER_LENGTH + (countInCurrentBucket * HASH_CODE_LEN), hashCode); // hash code currentBucket.putLong( currentBucketOffset + BUCKET_POINTER_START_OFFSET + (countInCurrentBucket * POINTER_LEN), pointer); // pointer currentBucket.putInt(currentBucketOffset + HEADER_COUNT_OFFSET, countInCurrentBucket + 1); // update count } else { // we need a new overflow bucket MemorySegment overflowSeg; final int overflowBucketNum; final int overflowBucketOffset; // first, see if there is space for an overflow bucket remaining in the last overflow segment if (partition.nextOverflowBucket == 0) { // no space left in last bucket, or no bucket yet, so create an overflow segment overflowSeg = getNextBuffer(); overflowBucketOffset = 0; overflowBucketNum = partition.numOverflowSegments; // add the new overflow segment if (partition.overflowSegments.length <= partition.numOverflowSegments) { MemorySegment[] newSegsArray = new MemorySegment[partition.overflowSegments.length * 2]; System.arraycopy(partition.overflowSegments, 0, newSegsArray, 0, partition.overflowSegments.length); partition.overflowSegments = newSegsArray; } partition.overflowSegments[partition.numOverflowSegments] = overflowSeg; partition.numOverflowSegments++; } else { // there is space in the last overflow segment overflowBucketNum = partition.numOverflowSegments - 1; overflowSeg = partition.overflowSegments[overflowBucketNum]; overflowBucketOffset = partition.nextOverflowBucket << NUM_INTRA_BUCKET_BITS; } // next overflow bucket is one ahead. if the segment is full, the next will be at the beginning // of a new segment partition.nextOverflowBucket = (partition.nextOverflowBucket == this.bucketsPerSegmentMask ? 0 : partition.nextOverflowBucket + 1); // insert the new overflow bucket in the chain of buckets // 1) set the old forward pointer // 2) let the bucket in the main table point to this one overflowSeg.putLong(overflowBucketOffset + HEADER_FORWARD_OFFSET, currentForwardPointer); final long pointerToNewBucket = (((long) overflowBucketNum) << 32) | ((long) overflowBucketOffset); originalBucket.putLong(originalBucketOffset + HEADER_FORWARD_OFFSET, pointerToNewBucket); // finally, insert the values into the overflow buckets overflowSeg.putInt(overflowBucketOffset + BUCKET_HEADER_LENGTH, hashCode); // hash code overflowSeg.putLong(overflowBucketOffset + BUCKET_POINTER_START_OFFSET, pointer); // pointer // set the count to one overflowSeg.putInt(overflowBucketOffset + HEADER_COUNT_OFFSET, 1); } } // -------------------------------------------------------------------------------------------- // Setup and Tear Down of Structures // -------------------------------------------------------------------------------------------- private void createPartitions(int numPartitions) { this.partitions.clear(); ListMemorySegmentSource memSource = new ListMemorySegmentSource(this.availableMemory); this.pageSizeInBits = MathUtils.log2strict(this.segmentSize); for (int i = 0; i < numPartitions; i++) { this.partitions.add(new InMemoryPartition<T>(this.buildSideSerializer, i, memSource, this.segmentSize, pageSizeInBits)); } this.compactionMemory = new InMemoryPartition<T>(this.buildSideSerializer, -1, memSource, this.segmentSize, pageSizeInBits); } private void clearPartitions() { for (int i = 0; i < this.partitions.size(); i++) { InMemoryPartition<T> p = this.partitions.get(i); p.clearAllMemory(this.availableMemory); } this.partitions.clear(); this.compactionMemory.clearAllMemory(availableMemory); } private void initTable(int numBuckets, byte numPartitions) { final int bucketsPerSegment = this.bucketsPerSegmentMask + 1; final int numSegs = (numBuckets >>> this.bucketsPerSegmentBits) + ((numBuckets & this.bucketsPerSegmentMask) == 0 ? 0 : 1); final MemorySegment[] table = new MemorySegment[numSegs]; // go over all segments that are part of the table for (int i = 0, bucket = 0; i < numSegs && bucket < numBuckets; i++) { final MemorySegment seg = getNextBuffer(); // go over all buckets in the segment for (int k = 0; k < bucketsPerSegment && bucket < numBuckets; k++, bucket++) { final int bucketOffset = k * HASH_BUCKET_SIZE; // compute the partition that the bucket corresponds to final byte partition = assignPartition(bucket, numPartitions); // initialize the header fields seg.put(bucketOffset + HEADER_PARTITION_OFFSET, partition); seg.putInt(bucketOffset + HEADER_COUNT_OFFSET, 0); seg.putLong(bucketOffset + HEADER_FORWARD_OFFSET, BUCKET_FORWARD_POINTER_NOT_SET); } table[i] = seg; } this.buckets = table; this.numBuckets = numBuckets; } private void releaseTable() { // set the counters back this.numBuckets = 0; if (this.buckets != null) { for (int i = 0; i < this.buckets.length; i++) { this.availableMemory.add(this.buckets[i]); } this.buckets = null; } } private final MemorySegment getNextBuffer() { // check if the list directly offers memory int s = this.availableMemory.size(); if (s > 0) { return this.availableMemory.remove(s - 1); } else { throw new RuntimeException("Memory ran out. numPartitions: " + this.partitions.size() + " minPartition: " + getMinPartition() + " maxPartition: " + getMaxPartition() + " bucketSize: " + this.buckets.length); //throw new RuntimeException("The hash table ran out of memory."); } } // -------------------------------------------------------------------------------------------- // Utility Computational Functions // -------------------------------------------------------------------------------------------- /** * Gets the number of partitions to be used for an initial hash-table, when no estimates are * available. * <p> * The current logic makes sure that there are always between 10 and 127 partitions, and close * to 0.1 of the number of buffers. * * @param numBuffers The number of buffers available. * @return The number of partitions to use. */ private static final int getPartitioningFanOutNoEstimates(int numBuffers) { return Math.max(10, Math.min(numBuffers / 10, MAX_NUM_PARTITIONS)); } private int getMaxPartition() { int maxPartition = 0; for (InMemoryPartition<T> p1 : this.partitions) { if (p1.getBlockCount() > maxPartition) { maxPartition = p1.getBlockCount(); } } return maxPartition; } private int getMinPartition() { int minPartition = Integer.MAX_VALUE; for (InMemoryPartition<T> p1 : this.partitions) { if (p1.getBlockCount() < minPartition) { minPartition = p1.getBlockCount(); } } return minPartition; } private static final int getInitialTableSize(int numBuffers, int bufferSize, int numPartitions, int recordLenBytes) { // ---------------------------------------------------------------------------------------- // the following observations hold: // 1) If the records are assumed to be very large, then many buffers need to go to the partitions // and fewer to the table // 2) If the records are small, then comparatively many have to go to the buckets, and fewer to the // partitions // 3) If the bucket-table is chosen too small, we will eventually get many collisions and will grow the // hash table, incrementally adding buffers. // 4) If the bucket-table is chosen to be large and we actually need more buffers for the partitions, we // cannot subtract them afterwards from the table // // ==> We start with a comparatively small hash-table. We aim for a 200% utilization of the bucket table // when all the partition buffers are full. Most likely, that will cause some buckets to be re-hashed // and grab additional buffers away from the partitions. // NOTE: This decision may be subject to changes after conclusive experiments! // ---------------------------------------------------------------------------------------- final long totalSize = ((long) bufferSize) * numBuffers; final long numRecordsStorable = totalSize / (recordLenBytes + RECORD_OVERHEAD_BYTES); final long bucketBytes = numRecordsStorable * RECORD_TABLE_BYTES; final long numBuckets = bucketBytes / (2 * HASH_BUCKET_SIZE) + 1; return numBuckets > Integer.MAX_VALUE ? Integer.MAX_VALUE : (int) numBuckets; } /** * Assigns a partition to a bucket. * * @param bucket bucket index * @param numPartitions number of partitions * @return The hash code for the integer. */ private static final byte assignPartition(int bucket, byte numPartitions) { return (byte) (bucket % numPartitions); } /** * Compacts (garbage collects) partition with copy-compact strategy using compaction partition * * @param partition partition number * @throws IOException */ private void compactPartition(int partitionNumber) throws IOException { // stop if no garbage exists if (this.partitions.get(partitionNumber).isCompacted()) { return; } // release all segments owned by compaction partition this.compactionMemory.clearAllMemory(availableMemory); this.compactionMemory.allocateSegments(1); T tempHolder = this.buildSideSerializer.createInstance(); InMemoryPartition<T> partition = this.partitions.remove(partitionNumber); final int numPartitions = this.partitions.size() + 1; // dropped one earlier long pointer = 0L; int pointerOffset = 0; int bucketOffset = 0; final int bucketsPerSegment = this.bucketsPerSegmentMask + 1; for (int i = 0, bucket = partitionNumber; i < this.buckets.length && bucket < this.numBuckets; i++) { MemorySegment segment = this.buckets[i]; // go over all buckets in the segment belonging to the partition for (int k = bucket % bucketsPerSegment; k < bucketsPerSegment && bucket < this.numBuckets; k += numPartitions, bucket += numPartitions) { bucketOffset = k * HASH_BUCKET_SIZE; if ((int) segment.get(bucketOffset + HEADER_PARTITION_OFFSET) != partitionNumber) { throw new IOException("Accessed wrong bucket! "); } int count = segment.getInt(bucketOffset + HEADER_COUNT_OFFSET); for (int j = 0; j < NUM_ENTRIES_PER_BUCKET && j < count; j++) { pointerOffset = bucketOffset + BUCKET_POINTER_START_OFFSET + (j * POINTER_LEN); pointer = segment.getLong(pointerOffset); partition.readRecordAt(pointer, tempHolder); pointer = this.compactionMemory.appendRecord(tempHolder); segment.putLong(pointerOffset, pointer); } long overflowPointer = segment.getLong(bucketOffset + HEADER_FORWARD_OFFSET); if (overflowPointer != BUCKET_FORWARD_POINTER_NOT_SET) { // scan overflow buckets int current = NUM_ENTRIES_PER_BUCKET; bucketOffset = (int) (overflowPointer & 0xffffffff); pointerOffset = ((int) (overflowPointer & 0xffffffff)) + BUCKET_POINTER_START_OFFSET; int overflowSegNum = (int) (overflowPointer >>> 32); count += partition.overflowSegments[overflowSegNum].getInt(bucketOffset + HEADER_COUNT_OFFSET); while (current < count) { pointer = partition.overflowSegments[overflowSegNum].getLong(pointerOffset); partition.readRecordAt(pointer, tempHolder); pointer = this.compactionMemory.appendRecord(tempHolder); partition.overflowSegments[overflowSegNum].putLong(pointerOffset, pointer); current++; if (current % NUM_ENTRIES_PER_BUCKET == 0) { count += partition.overflowSegments[overflowSegNum] .getInt(bucketOffset + HEADER_COUNT_OFFSET); overflowPointer = partition.overflowSegments[overflowSegNum] .getLong(bucketOffset + HEADER_FORWARD_OFFSET); if (overflowPointer == BUCKET_FORWARD_POINTER_NOT_SET) { break; } overflowSegNum = (int) (overflowPointer >>> 32); bucketOffset = (int) (overflowPointer & 0xffffffff); pointerOffset = ((int) (overflowPointer & 0xffffffff)) + BUCKET_POINTER_START_OFFSET; } else { pointerOffset += POINTER_LEN; } } } } } // swap partition with compaction partition this.compactionMemory.setPartitionNumber(partitionNumber); this.partitions.add(partitionNumber, compactionMemory); this.compactionMemory = partition; this.partitions.get(partitionNumber).overflowSegments = this.compactionMemory.overflowSegments; this.partitions.get(partitionNumber).numOverflowSegments = this.compactionMemory.numOverflowSegments; this.partitions.get(partitionNumber).nextOverflowBucket = this.compactionMemory.nextOverflowBucket; this.partitions.get(partitionNumber).setCompaction(true); this.compactionMemory.resetRecordCounter(); this.compactionMemory.setPartitionNumber(-1); // try to allocate maximum segment count int maxSegmentNumber = 0; for (InMemoryPartition<T> e : this.partitions) { if (e.getBlockCount() > maxSegmentNumber) { maxSegmentNumber = e.getBlockCount(); } } this.compactionMemory.allocateSegments(maxSegmentNumber); if (this.compactionMemory.getBlockCount() > maxSegmentNumber) { this.compactionMemory.releaseSegments(maxSegmentNumber, availableMemory); } } /** * Compacts partition but may not reclaim all garbage * * @param partition partition number * @throws IOException */ @SuppressWarnings("unused") private void fastCompactPartition(int partitionNumber) throws IOException { // stop if no garbage exists if (this.partitions.get(partitionNumber).isCompacted()) { return; } //TODO IMPLEMENT ME return; } /** * This function hashes an integer value. It is adapted from Bob Jenkins' website * <a href="http://www.burtleburtle.net/bob/hash/integer.html">http://www.burtleburtle.net/bob/hash/integer.html</a>. * The hash function has the <i>full avalanche</i> property, meaning that every bit of the value to be hashed * affects every bit of the hash value. * * @param code The integer to be hashed. * @return The hash code for the integer. */ private static final int hash(int code) { code = (code + 0x7ed55d16) + (code << 12); code = (code ^ 0xc761c23c) ^ (code >>> 19); code = (code + 0x165667b1) + (code << 5); code = (code + 0xd3a2646c) ^ (code << 9); code = (code + 0xfd7046c5) + (code << 3); code = (code ^ 0xb55a4f09) ^ (code >>> 16); return code >= 0 ? code : -(code + 1); } /** * Iterator that traverses the whole hash table once * * If entries are inserted during iteration they may be overlooked by the iterator */ public class EntryIterator implements MutableObjectIterator<T> { private CompactingHashTable<T> table; private ArrayList<T> cache; // holds full bucket including its overflow buckets private int currentBucketIndex = 0; private int currentSegmentIndex = 0; private int currentBucketOffset = 0; private int bucketsPerSegment; private boolean done; private EntryIterator(CompactingHashTable<T> compactingHashTable) { this.table = compactingHashTable; this.cache = new ArrayList<T>(64); this.done = false; this.bucketsPerSegment = table.bucketsPerSegmentMask + 1; } @Override public T next(T reuse) throws IOException { if (done) { return null; } else if (!cache.isEmpty()) { reuse = cache.remove(cache.size() - 1); return reuse; } else { while (!done && cache.isEmpty()) { done = !fillCache(); } if (!done) { reuse = cache.remove(cache.size() - 1); return reuse; } else { return null; } } } private boolean fillCache() throws IOException { if (currentBucketIndex >= table.numBuckets) { return false; } MemorySegment bucket = table.buckets[currentSegmentIndex]; // get the basic characteristics of the bucket final int partitionNumber = bucket.get(currentBucketOffset + HEADER_PARTITION_OFFSET); final InMemoryPartition<T> partition = table.partitions.get(partitionNumber); final MemorySegment[] overflowSegments = partition.overflowSegments; int countInSegment = bucket.getInt(currentBucketOffset + HEADER_COUNT_OFFSET); int numInSegment = 0; int posInSegment = currentBucketOffset + BUCKET_POINTER_START_OFFSET; int bucketOffset = currentBucketOffset; // loop over all segments that are involved in the bucket (original bucket plus overflow buckets) while (true) { while (numInSegment < countInSegment) { long pointer = bucket.getLong(posInSegment); posInSegment += POINTER_LEN; numInSegment++; T target = table.buildSideSerializer.createInstance(); try { partition.readRecordAt(pointer, target); cache.add(target); } catch (IOException e) { throw new RuntimeException( "Error deserializing record from the hashtable: " + e.getMessage(), e); } } // this segment is done. check if there is another chained bucket final long forwardPointer = bucket.getLong(bucketOffset + HEADER_FORWARD_OFFSET); if (forwardPointer == BUCKET_FORWARD_POINTER_NOT_SET) { break; } final int overflowSegNum = (int) (forwardPointer >>> 32); bucket = overflowSegments[overflowSegNum]; bucketOffset = (int) (forwardPointer & 0xffffffff); countInSegment = bucket.getInt(bucketOffset + HEADER_COUNT_OFFSET); posInSegment = bucketOffset + BUCKET_POINTER_START_OFFSET; numInSegment = 0; } currentBucketIndex++; if (currentBucketIndex % bucketsPerSegment == 0) { currentSegmentIndex++; currentBucketOffset = 0; } else { currentBucketOffset += HASH_BUCKET_SIZE; } return true; } } public final class HashTableProber<PT> extends AbstractHashTableProber<PT, T> { private InMemoryPartition<T> partition; private MemorySegment bucket; private int pointerOffsetInBucket; private HashTableProber(TypeComparator<PT> probeTypeComparator, TypePairComparator<PT, T> pairComparator) { super(probeTypeComparator, pairComparator); } public boolean getMatchFor(PT probeSideRecord, T targetForMatch) { final int searchHashCode = hash(this.probeTypeComparator.hash(probeSideRecord)); final int posHashCode = searchHashCode % numBuckets; // get the bucket for the given hash code MemorySegment bucket = buckets[posHashCode >> bucketsPerSegmentBits]; int bucketInSegmentOffset = (posHashCode & bucketsPerSegmentMask) << NUM_INTRA_BUCKET_BITS; // get the basic characteristics of the bucket final int partitionNumber = bucket.get(bucketInSegmentOffset + HEADER_PARTITION_OFFSET); final InMemoryPartition<T> partition = partitions.get(partitionNumber); final MemorySegment[] overflowSegments = partition.overflowSegments; this.pairComparator.setReference(probeSideRecord); int countInSegment = bucket.getInt(bucketInSegmentOffset + HEADER_COUNT_OFFSET); int numInSegment = 0; int posInSegment = bucketInSegmentOffset + BUCKET_HEADER_LENGTH; // loop over all segments that are involved in the bucket (original bucket plus overflow buckets) while (true) { while (numInSegment < countInSegment) { final int thisCode = bucket.getInt(posInSegment); posInSegment += HASH_CODE_LEN; // check if the hash code matches if (thisCode == searchHashCode) { // get the pointer to the pair final int pointerOffset = bucketInSegmentOffset + BUCKET_POINTER_START_OFFSET + (numInSegment * POINTER_LEN); final long pointer = bucket.getLong(pointerOffset); numInSegment++; // deserialize the key to check whether it is really equal, or whether we had only a hash collision try { partition.readRecordAt(pointer, targetForMatch); if (this.pairComparator.equalToReference(targetForMatch)) { this.partition = partition; this.bucket = bucket; this.pointerOffsetInBucket = pointerOffset; return true; } } catch (IOException e) { throw new RuntimeException( "Error deserializing record from the hashtable: " + e.getMessage(), e); } } else { numInSegment++; } } // this segment is done. check if there is another chained bucket final long forwardPointer = bucket.getLong(bucketInSegmentOffset + HEADER_FORWARD_OFFSET); if (forwardPointer == BUCKET_FORWARD_POINTER_NOT_SET) { return false; } final int overflowSegNum = (int) (forwardPointer >>> 32); bucket = overflowSegments[overflowSegNum]; bucketInSegmentOffset = (int) (forwardPointer & 0xffffffff); countInSegment = bucket.getInt(bucketInSegmentOffset + HEADER_COUNT_OFFSET); posInSegment = bucketInSegmentOffset + BUCKET_HEADER_LENGTH; numInSegment = 0; } } public void updateMatch(T record) throws IOException { long newPointer = this.partition.appendRecord(record); this.bucket.putLong(this.pointerOffsetInBucket, newPointer); this.partition.setCompaction(false); //FIXME Do we really create garbage here? } } }