Use soft values in the EntityCache; approximate entity size #490
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| /* | ||
| * 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.polaris.core.persistence.cache; | ||
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| import com.github.benmanes.caffeine.cache.Weigher; | ||
| import org.checkerframework.checker.index.qual.NonNegative; | ||
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| /** | ||
| * A {@link Weigher} implementation that weighs {@link EntityCacheEntry} objects by the approximate | ||
| * size of the entity object. | ||
| */ | ||
| public class EntityWeigher implements Weigher<Long, EntityCacheEntry> { | ||
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| /** The amount of weight that is expected to roughly equate to 1MB of memory usage */ | ||
| public static final long WEIGHT_PER_MB = 1024 * 1024; | ||
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| /* Represents the approximate size of an entity beyond the properties */ | ||
| private static final int APPROXIMATE_ENTITY_OVERHEAD = 1000; | ||
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There was a problem hiding this comment. Where does the value 1000 come from? There was a problem hiding this comment. See this old comment -- the apparent assumption was that entities are generally ~1KB. This means in the worst case, we will not get a larger number of entries due to this change. It should strictly be smaller. |
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| /** Singleton instance */ | ||
| private static final EntityWeigher instance = new EntityWeigher(); | ||
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| private EntityWeigher() {} | ||
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| /** Gets the singleton {@link EntityWeigher} */ | ||
| public static EntityWeigher getInstance() { | ||
| return instance; | ||
| } | ||
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| /** | ||
| * Computes the weight of a given entity | ||
| * | ||
| * @param key The entity's key; not used | ||
| * @param value The entity to be cached | ||
| * @return The weight of the entity | ||
| */ | ||
| @Override | ||
| public @NonNegative int weigh(Long key, EntityCacheEntry value) { | ||
| return APPROXIMATE_ENTITY_OVERHEAD | ||
| + value.getEntity().getProperties().length() | ||
| + value.getEntity().getInternalProperties().length(); | ||
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There was a problem hiding this comment. The assumption here is wrong. There is no guarantee that one character is only one byte, even with "compact strings" - it's likely off by factor 2. There was a problem hiding this comment. It's an approximate size. Even if it's off by a factor of 10, that should be okay. A 1GB cache is greatly preferable to an unbounded cache. |
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| } | ||
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| /** Factory method to provide a typed Weigher */ | ||
| public static Weigher<Long, EntityCacheEntry> asWeigher() { | ||
| return (Weigher<Long, EntityCacheEntry>) getInstance(); | ||
| } | ||
| } | ||
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While we're here - why is this always hard coded and not configurable? Or at least determined based on the actual heap size (which is not as easy as it sounds)?
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This is a good callout. My concern with making it configurable is that the limit is close to arbitrary.
As you noted in another comment, we have a "goal" of 100MB but that could really be 200MB or 1MB depending on how eviction happens with soft values and the weights. So while raising the limit definitely gets you a bigger cache, it's quite opaque as to what value you would actually want to set.
Also, the EntityCache is ideally very transparent and not something a typical end user would want to concern themselves with.
In light of the above I kept it hard-coded for now but if you feel strongly that we should make it a
featureConfigurationI am comfortable doing so