[GitHub] [hudi] alexeykudinkin commented on a change in pull request #4520: [HUDI-3179] Extracted common `AbstractHoodieTableFileIndex` to be shared across engines

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alexeykudinkin commented on a change in pull request #4520:
URL: https://github.com/apache/hudi/pull/4520#discussion_r784472444



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File path: hudi-spark-datasource/hudi-spark/src/main/scala/org/apache/hudi/AbstractHoodieTableFileIndex.scala
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@@ -0,0 +1,309 @@
+/*
+ * 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.hudi
+
+import org.apache.hadoop.fs.{FileStatus, Path}
+import org.apache.hudi.DataSourceReadOptions.{QUERY_TYPE, QUERY_TYPE_SNAPSHOT_OPT_VAL}
+import org.apache.hudi.common.config.{HoodieMetadataConfig, TypedProperties}
+import org.apache.hudi.common.engine.HoodieEngineContext
+import org.apache.hudi.common.fs.FSUtils
+import org.apache.hudi.common.model.FileSlice
+import org.apache.hudi.common.model.HoodieTableType.MERGE_ON_READ
+import org.apache.hudi.common.table.HoodieTableMetaClient
+import org.apache.hudi.common.table.view.{FileSystemViewStorageConfig, HoodieTableFileSystemView}
+
+import scala.collection.JavaConversions._
+import scala.collection.JavaConverters._
+import scala.collection.mutable
+
+/**
+ * A file index which support partition prune for hoodie snapshot and read-optimized query.
+ *
+ * Main steps to get the file list for query:
+ * 1、Load all files and partition values from the table path.
+ * 2、Do the partition prune by the partition filter condition.
+ *
+ * There are 3 cases for this:
+ * 1、If the partition columns size is equal to the actually partition path level, we
+ * read it as partitioned table.(e.g partition column is "dt", the partition path is "2021-03-10")
+ *
+ * 2、If the partition columns size is not equal to the partition path level, but the partition
+ * column size is "1" (e.g. partition column is "dt", but the partition path is "2021/03/10"
+ * who's directory level is 3).We can still read it as a partitioned table. We will mapping the
+ * partition path (e.g. 2021/03/10) to the only partition column (e.g. "dt").
+ *
+ * 3、Else the the partition columns size is not equal to the partition directory level and the
+ * size is great than "1" (e.g. partition column is "dt,hh", the partition path is "2021/03/10/12"),
+ * we read it as a Non-Partitioned table because we cannot know how to mapping the partition
+ * path with the partition columns in this case.
+ *
+ */
+abstract class AbstractHoodieTableFileIndex(engineContext: HoodieEngineContext,

Review comment:
       Agreed, some sort of guideline would be helpful to make sure code base is consistent.
   
   I usually following the rule of
     - If it contains some functionality that *has to* be extended (ie abstract class) then i go for `Abstract`
     - If it's just extracts some common functionality, but isn't abstract i go for `Base`
   
   




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