heyihong commented on code in PR #53625: URL: https://github.com/apache/spark/pull/53625#discussion_r2655856043
########## common/utils-java/src/main/java/org/apache/spark/util/UUIDv7Generator.java: ########## @@ -0,0 +1,60 @@ +/* + * 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.spark.util; + +import java.util.UUID; +import java.util.concurrent.ThreadLocalRandom; + +/** + * Generator for UUIDv7 as defined in RFC 9562. + * https://www.rfc-editor.org/rfc/rfc9562.html + * + * UUIDv7 is a time-ordered UUID that embeds a Unix timestamp in milliseconds. + * + * Monotonicity is best-effort but not strictly guaranteed by this implementation, + * in rare cases such as concurrent generation within the same millisecond or clock adjustments. + * This trade-off is intentional to avoid throughput degradation or thread contention. + */ +public final class UUIDv7Generator { + + private UUIDv7Generator() { + // Prevent instantiation, as this is a util class. + } + + /** + * Generate a UUIDv7 from the current time. + * + * The generated UUID embeds a 48-bit Unix timestamp (milliseconds since epoch), + * followed by random bits for uniqueness. Monotonicity is best-effort: UUIDs + * generated across different milliseconds will be ordered, but UUIDs within + * the same millisecond may have random ordering. + * + * @return a new UUIDv7 + */ + public static UUID generate() { + long timestamp = System.currentTimeMillis(); + + // 48-bit timestamp | 4-bit version (0111) | 12-bit rand_a + long msb = (timestamp << 16) | (0x7L << 12) | (ThreadLocalRandom.current().nextInt() & 0xFFF); Review Comment: @asl3 One more thing worth mentioning is that **instances of ThreadLocalRandom are not cryptographically secure**, according to https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/util/concurrent/ThreadLocalRandom.html. That is also not the best practice according to [Section 6.9](https://www.rfc-editor.org/rfc/rfc9562.html#name-unguessability). It may be worth considering fixing it, since uniqueness is essential for a UUID. ``` Implementations SHOULD utilize a cryptographically secure pseudorandom number generator (CSPRNG) to provide values that are both difficult to predict ("unguessable") and have a low likelihood of collision ("unique"). ``` -- 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: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
