heyihong commented on code in PR #53625: URL: https://github.com/apache/spark/pull/53625#discussion_r2653044290
########## common/utils-java/src/main/java/org/apache/spark/util/UUIDv7Generator.java: ########## @@ -0,0 +1,67 @@ +/* + * 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; +import java.util.concurrent.atomic.AtomicLong; + +/** + * 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. + * + * The generate() method guarantees monotonicity by tracking the last used timestamp + * and increments if necessary when the clock hasn't advanced. Review Comment: Monotonicity is a desirable property for time-based, sortable UUIDs. If event A happens before event B within a process, we may want the UUIDv7 of event A to be smaller than the UUIDv7 of event B, so that their order is preserved when sorting. The current implementation may cause some timestamps to exhibit noticeable drift when generating a large number of UUIDs in a short period of time, because we increment the millisecond value. An alternative solution is to store some nanosecond information in rand_a and increment rand_a as a sequence number. Here is a reference implementation of UUIDv7 in Go: https://github.com/google/uuid/blob/master/version7.go#L88-L104 cc: @asl3 -- 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]
