Github user rxin commented on a diff in the pull request:
https://github.com/apache/spark/pull/11750#discussion_r56394213
--- Diff:
sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/catalog/SessionCatalog.scala
---
@@ -0,0 +1,484 @@
+/*
+ * 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.catalyst.catalog
+
+import java.util.concurrent.ConcurrentHashMap
+
+import scala.collection.JavaConverters._
+
+import org.apache.spark.sql.AnalysisException
+import org.apache.spark.sql.catalyst.{FunctionIdentifier, TableIdentifier}
+import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan,
SubqueryAlias}
+
+
+/**
+ * An internal catalog that is used by a Spark Session. This internal
catalog serves as a
+ * proxy to the underlying metastore (e.g. Hive Metastore) and it also
manages temporary
+ * tables and functions of the Spark Session that it belongs to.
+ */
+class SessionCatalog(externalCatalog: ExternalCatalog) {
+ import ExternalCatalog._
+
+ private[this] val tempTables = new ConcurrentHashMap[String, LogicalPlan]
+
+ private[this] val tempFunctions = new ConcurrentHashMap[String,
CatalogFunction]
+
+ //
----------------------------------------------------------------------------
+ // Databases
+ //
----------------------------------------------------------------------------
+ // All methods in this category interact directly with the underlying
catalog.
+ //
----------------------------------------------------------------------------
+
+ def createDatabase(dbDefinition: CatalogDatabase, ignoreIfExists:
Boolean): Unit = {
+ externalCatalog.createDatabase(dbDefinition, ignoreIfExists)
+ }
+
+ def dropDatabase(db: String, ignoreIfNotExists: Boolean, cascade:
Boolean): Unit = {
+ externalCatalog.dropDatabase(db, ignoreIfNotExists, cascade)
+ }
+
+ def alterDatabase(dbDefinition: CatalogDatabase): Unit = {
+ externalCatalog.alterDatabase(dbDefinition)
+ }
+
+ def getDatabase(db: String): CatalogDatabase = {
+ externalCatalog.getDatabase(db)
+ }
+
+ def databaseExists(db: String): Boolean = {
+ externalCatalog.databaseExists(db)
+ }
+
+ def listDatabases(): Seq[String] = {
+ externalCatalog.listDatabases()
+ }
+
+ def listDatabases(pattern: String): Seq[String] = {
+ externalCatalog.listDatabases(pattern)
+ }
+
+ //
----------------------------------------------------------------------------
+ // Tables
+ //
----------------------------------------------------------------------------
+ // There are two kinds of tables, temporary tables and metastore tables.
+ // Temporary tables are isolated across sessions and do not belong to any
+ // particular database. Metastore tables can be used across multiple
+ // sessions as their metadata is persisted in the underlying catalog.
+ //
----------------------------------------------------------------------------
+
+ // ----------------------------------------------------
+ // | Methods that interact with metastore tables only |
+ // ----------------------------------------------------
+
+ /**
+ * Create a metastore table in the database specified in
`tableDefinition`.
+ * If no such database is specified, create it in the current database.
+ */
+ def createTable(
+ currentDb: String,
--- End diff --
make sure we document that in the session catalog code and explain why we
are tracking current db in here.
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