VladRodionov commented on code in PR #8155: URL: https://github.com/apache/hbase/pull/8155#discussion_r3156130060
########## hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/cache/CacheEngine.java: ########## @@ -0,0 +1,302 @@ +/* + * 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.hadoop.hbase.io.hfile.cache; + +import java.util.Optional; +import org.apache.hadoop.conf.Configuration; +import org.apache.hadoop.hbase.io.hfile.BlockCacheKey; +import org.apache.hadoop.hbase.io.hfile.BlockType; +import org.apache.hadoop.hbase.io.hfile.CacheStats; +import org.apache.hadoop.hbase.io.hfile.Cacheable; +import org.apache.hadoop.hbase.io.hfile.HFileBlock; +import org.apache.yetus.audience.InterfaceAudience; + +/** + * Storage abstraction for a concrete HBase block cache backend. + * <p> + * A {@code CacheEngine} represents the storage layer only. It is responsible for storing, + * retrieving, invalidating, and reporting statistics for cached blocks. It does not perform tier + * orchestration, admission control, placement decisions, or promotion/demotion across cache levels. + * </p> + * <p> + * This interface is intentionally aligned with the storage-oriented subset of the current + * {@code BlockCache} contract so that existing implementations such as LruBlockCache and + * BucketCache can be migrated incrementally with minimal behavioral risk. + * </p> + * <p> + * Responsibilities of a {@code CacheEngine} include: + * </p> + * <ul> + * <li>block lookup</li> + * <li>block insertion</li> + * <li>targeted invalidation / eviction</li> + * <li>capacity and occupancy reporting</li> + * <li>engine-local statistics</li> + * <li>optional implementation-specific fit/capability checks</li> + * </ul> + * <p> + * Non-responsibilities include: + * </p> + * <ul> + * <li>L1/L2 topology orchestration</li> + * <li>admission policy</li> + * <li>tier placement decisions</li> + * <li>promotion or demotion across tiers</li> + * </ul> + */ [email protected] +public interface CacheEngine { + + /** + * Returns a human-readable name for this cache engine instance. + * <p> + * The name is intended for logging, metrics, diagnostics, and configuration reporting. It should + * be stable for the lifetime of the engine instance. + * </p> + * @return engine name + */ + String getName(); + + /** + * Returns the engine type. + * <p> + * This identifies the concrete backend family, such as LRU, BUCKET, or CARROT. The type is useful + * for metrics, diagnostics, and topology assembly. + * </p> + * @return engine type + */ + CacheEngineType getType(); + + /** + * Adds a block to the cache. + * @param cacheKey block cache key + * @param buf block contents + * @param inMemory whether the block should be treated as in-memory + */ + void cacheBlock(BlockCacheKey cacheKey, Cacheable buf, boolean inMemory); + + /** + * Adds a block to the cache, optionally waiting for asynchronous cache backends. + * <p> + * This is primarily useful for implementations such as BucketCache that may buffer writes + * asynchronously. + * </p> + * @param cacheKey block cache key + * @param buf block contents + * @param inMemory whether the block should be treated as in-memory + * @param waitWhenCache whether to wait for the cache operation to be accepted/flushed + */ + default void cacheBlock(BlockCacheKey cacheKey, Cacheable buf, boolean inMemory, + boolean waitWhenCache) { + cacheBlock(cacheKey, buf, inMemory); + } + + /** + * Adds a block to the cache, defaulting to non in-memory treatment. + * @param cacheKey block cache key + * @param buf block contents + */ + void cacheBlock(BlockCacheKey cacheKey, Cacheable buf); + + /** + * Fetches a block from the cache. + * @param cacheKey block to fetch + * @param caching whether caching is enabled for the request; used for metrics + * @param repeat whether this is a repeated lookup for the same block; used to avoid + * double-counting misses + * @param updateCacheMetrics whether cache metrics should be updated + * @return cached block, or {@code null} if not present + */ + Cacheable getBlock(BlockCacheKey cacheKey, boolean caching, boolean repeat, + boolean updateCacheMetrics); + + /** + * Fetches a block from the cache with an optional block type hint. + * <p> + * Implementations may ignore the block type if it is not needed. + * </p> + * @param cacheKey block to fetch + * @param caching whether caching is enabled for the request; used for metrics + * @param repeat whether this is a repeated lookup for the same block; used to avoid + * double-counting misses + * @param updateCacheMetrics whether cache metrics should be updated + * @param blockType optional block type hint + * @return cached block, or {@code null} if not present + */ + default Cacheable getBlock(BlockCacheKey cacheKey, boolean caching, boolean repeat, + boolean updateCacheMetrics, BlockType blockType) { Review Comment: BlockType here is a hint rather than part of the lookup key. It is used by some cache implementations to avoid re-inspecting the block payload (e.g. distinguishing data vs index/meta blocks), enabling minor optimizations in metrics, prioritization, or eviction behavior. It is not required for correctness and does not affect lookup, which is based solely on BlockCacheKey. Implementations are free to ignore it, which is why a default method is provided. This will be moved later into Context object -- 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]
