[GitHub] [spark] rdblue commented on a change in pull request #24246: [SPARK-24252][SQL] Add TableCatalog API (WIP)

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rdblue commented on a change in pull request #24246: [SPARK-24252][SQL] Add TableCatalog API (WIP)
URL: https://github.com/apache/spark/pull/24246#discussion_r272282840
 
 

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 File path: sql/catalyst/src/main/java/org/apache/spark/sql/catalog/v2/TableCatalog.java
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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.spark.sql.catalog.v2;
+
+import org.apache.spark.sql.catalog.v2.expressions.Transform;
+import org.apache.spark.sql.catalyst.analysis.NoSuchTableException;
+import org.apache.spark.sql.catalyst.analysis.TableAlreadyExistsException;
+import org.apache.spark.sql.types.StructType;
+
+import java.util.Collections;
+import java.util.Map;
+
+/**
+ * Catalog methods for working with Tables.
+ */
+public interface TableCatalog extends CatalogPlugin {
+  /**
+   * List the tables in a namespace from the catalog.
+   *
+   * @param namespace a multi-part namespace
+   * @return an array of Identifiers for tables
+   */
+  Identifier[] listTables(String[] namespace);
+
+  /**
+   * Load table metadata by {@link Identifier identifier} from the catalog.
+   *
+   * @param ident a table identifier
+   * @return the table's metadata
+   * @throws NoSuchTableException If the table doesn't exist.
+   */
+  Table loadTable(Identifier ident) throws NoSuchTableException;
+
+  /**
+   * Refresh table metadata for {@link Identifier identifier}.
+   * <p>
+   * If the table is already loaded or cached, drop cached data and reload it. If the table is not
 
 Review comment:
   Right now, we've implemented caching in our catalogs. Spark always calls load and uses the version that is returned instead of caching. Our catalog then uses a weak reference in the cache so that the version is periodically updated when no more queries are running against that version.
   
   I'm not sure whether Spark should have some caching above the catalog or if the catalog should be responsible for this. Let's plan on talking about this at the next sync.

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