vcrfxia commented on code in PR #13188: URL: https://github.com/apache/kafka/pull/13188#discussion_r1101902156
########## streams/src/main/java/org/apache/kafka/streams/state/VersionedKeyValueStore.java: ########## @@ -0,0 +1,99 @@ +/* + * 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.streams.state; + +import org.apache.kafka.streams.errors.InvalidStateStoreException; +import org.apache.kafka.streams.processor.StateStore; + +/** + * A key-value store that stores multiple record versions per key, and supports timestamp-based + * retrieval operations to return the latest record (per key) as of a specified timestamp. + * Only one record is stored per key and timestamp, i.e., a second call to + * {@link #put(Object, Object, long)} with the same key and timestamp will replace the first. + * <p> + * Each store instance has an associated, fixed-duration "history retention" which specifies + * how long old record versions should be kept for. In particular, a versioned store guarantees + * to return accurate results for calls to {@link #get(Object, long)} where the provided timestamp + * bound is within history retention of the current observed stream time. (Queries with timestamp + * bound older than the specified history retention are considered invalid.) + * + * @param <K> The key type + * @param <V> The value type + */ +public interface VersionedKeyValueStore<K, V> extends StateStore { + + /** + * Add a new record version associated with this key. + * + * @param key The key + * @param value The value, it can be {@code null}; + * if the serialized bytes are also {@code null} it is interpreted as a delete + * @param timestamp The timestamp for this record version + * @throws NullPointerException If {@code null} is used for key. + */ + void put(K key, V value, long timestamp); + + /** + * Delete the value associated with this key from the store, at the specified timestamp + * (if there is such a value), and return the deleted value. + * <p> + * This operation is semantically equivalent to {@link #get(Object, long)} #get(key, timestamp))} + * followed by {@link #put(Object, Object, long) #put(key, null, timestamp)}. + * + * @param key The key + * @param timestamp The timestamp for this delete + * @return The value and timestamp of the latest record associated with this key + * as of the deletion timestamp (inclusive), or {@code null} if any of + * (1) the store contains no records for this key, (2) the latest record + * for this key as of the deletion timestamp is a tombstone, or + * (3) the deletion timestamp is older than this store's history retention + * (i.e., this store no longer contains data for the provided timestamp). + * @throws NullPointerException If {@code null} is used for key. + */ + VersionedRecord<V> delete(K key, long timestamp); + + /** + * Get the latest (by timestamp) record associated with this key. + * + * @param key The key to fetch + * @return The value and timestamp of the latest record associated with this key, or + * {@code null} if either (1) the store contains no records for this key or (2) the + * latest record for this key is a tombstone. + * @throws NullPointerException If null is used for key. + * @throws InvalidStateStoreException if the store is not initialized + */ + VersionedRecord<V> get(K key); + + /** + * Get the latest record associated with this key with timestamp not exceeding the specified + * timestamp bound. Review Comment: Hm. Currently "validFrom" and "validTo" are not mentioned anywhere in the public-facing interfaces (VersionedKeyValueStore, VersionedRecord, etc) in javadocs or as parameter names; they are only "officially" introduced as concepts in the javadocs for RocksDBVersionedStore and its implementation helpers. I'm a bit hesitant to introduce these concepts in the public-facing docs at this time if the only purpose is to clarify what's returned from `get(key, asOfTimestamp)`, particularly because during KIP discussion one person mentioned that these terms did not feel intuitive to them. If you feel strongly though, I can move the explanation of "validity interval" including "validFrom" and "validTo" from the javadocs for RocksDBVersionedStore to VersionedKeyValueStore itself, and then update this javadoc. -- 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. 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