[GitHub] [pinot] ben-manes commented on a change in pull request #7409: Fix JSONPath cache inefficient issue

[GitBox <gi...@apache.org>]

ben-manes commented on a change in pull request #7409:
URL: https://github.com/apache/pinot/pull/7409#discussion_r710760248



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File path: pinot-common/src/main/java/org/apache/pinot/common/function/JsonPathMapCache.java
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@@ -0,0 +1,61 @@
+/**
+ * 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.pinot.common.function;
+
+import com.jayway.jsonpath.JsonPath;
+import com.jayway.jsonpath.spi.cache.Cache;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+/**
+ * This cache for avoiding repeatedly compiling JSON path string when using jsonPathXXX transformations
+ *
+ * <p>The existing jay way LRUCache is very inefficient, It will cause
+ * a lot of unnecessary lock waits during high concurrent data ingestion,
+ * and LRU mechanism is inappropriate for Pinot bounded size of the
+ * transformation config, so we should use this simple Map cache instead
+ * of it.

Review comment:
       You will likely be fine using Guava if you increase the concurrency level (e.g. to 64, defaults to 4). That will stripe the LRU so that there is less contention, but will still suffer at peak loads ([benchmarks](https://github.com/ben-manes/caffeine/wiki/Benchmarks#read-100-1)). For your use-case here that is likely good enough given other costs, e.g. JsonPath's [inefficiencies](https://github.com/json-path/JsonPath/issues/740). Unfortunately my patches to Guava that gave it a ~25x boost were not accepted due to a lack of a champion, and instead they simply updated the JavaDoc to recommend Caffeine. 🙂 




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