ijuma commented on code in PR #13042: URL: https://github.com/apache/kafka/pull/13042#discussion_r1055981406
########## storage/src/main/java/org/apache/kafka/server/log/internals/SkimpyOffsetMap.java: ########## @@ -0,0 +1,241 @@ +/* + * Licensed to the Apache Software Foundation (ASF) under one or more + * contributor license agreements. See the NOTICE file distributed with + * this work for additional information regarding copyright ownership. + * The ASF licenses this file to You 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 org.apache.kafka.server.log.internals; + +import org.apache.kafka.common.utils.ByteUtils; +import org.apache.kafka.common.utils.Utils; + +import java.nio.ByteBuffer; +import java.security.DigestException; +import java.security.MessageDigest; +import java.security.NoSuchAlgorithmException; +import java.util.Arrays; + +/** + * An hash table used for deduplicating the log. This hash table uses a cryptographicly secure hash of the key as a proxy for the key + * for comparisons and to save space on object overhead. Collisions are resolved by probing. This hash table does not support deletes. + */ +public class SkimpyOffsetMap implements OffsetMap { + + /** + * The number of bytes of space each entry uses (the number of bytes in the hash plus an 8 byte offset) + */ + public final int bytesPerEntry; + + private final ByteBuffer bytes; + + /* the hash algorithm instance to use */ + private final MessageDigest digest; + + /* the number of bytes for this hash algorithm */ + private final int hashSize; + + /** + * The maximum number of entries this map can contain + */ + private final int slots; + + /* cache some hash buffers to avoid reallocating each time */ + private final byte[] hash1; + private final byte[] hash2; + + /* number of entries put into the map */ + private int entries = 0; + + /* number of lookups on the map */ + private long lookups = 0L; + + /* the number of probes for all lookups */ + private long probes = 0L; + + /* the latest offset written into the map */ + private long lastOffset = -1L; + + /** + * Create an instance of SkimplyOffsetMap with the default hash algorithm (MD5). + * + * @param memory The amount of memory this map can use + */ + public SkimpyOffsetMap(int memory) throws NoSuchAlgorithmException { + this(memory, "MD5"); + } + + /** + * Create an instance of SkimpyOffsetMap. + * + * @param memory The amount of memory this map can use + * @param hashAlgorithm The hash algorithm instance to use: MD2, MD5, SHA-1, SHA-256, SHA-384, SHA-512 + */ + public SkimpyOffsetMap(int memory, String hashAlgorithm) throws NoSuchAlgorithmException { + this.bytes = ByteBuffer.allocate(memory); + + this.digest = MessageDigest.getInstance(hashAlgorithm); + + this.hashSize = digest.getDigestLength(); + this.bytesPerEntry = hashSize * 8; + this.slots = memory / bytesPerEntry; + + this.hash1 = new byte[hashSize]; + this.hash2 = new byte[hashSize]; + } + + @Override + public int slots() { + return slots; + } + + /** + * Get the offset associated with this key. + * @param key The key + * @return The offset associated with this key or -1 if the key is not found + */ + @Override + public long get(ByteBuffer key) throws DigestException { + ++lookups; + hashInto(key, hash1); + // search for the hash of this key by repeated probing until we find the hash we are looking for or we find an empty slot + int attempt = 0; + int pos = 0; + //we need to guard against attempt integer overflow if the map is full + //limit attempt to number of slots once positionOf(..) enters linear search mode + int maxAttempts = slots + hashSize - 4; + do { + if (attempt >= maxAttempts) + return -1L; + pos = positionOf(hash1, attempt); + bytes.position(pos); + if (isEmpty(pos)) + return -1L; + bytes.get(hash2); + ++attempt; + } while (!Arrays.equals(hash1, hash2)); + return bytes.getLong(); + } + + /** + * Associate this offset to the given key. + * @param key The key + * @param offset The offset + */ + @Override + public void put(ByteBuffer key, long offset) throws DigestException { + if (entries < slots) Review Comment: Good catch, the check needs to be reversed since I switched Scala's `require` to an `if`/`throw`. Fixed. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: jira-unsubscr...@kafka.apache.org For queries about this service, please contact Infrastructure at: us...@infra.apache.org
