rdblue commented on a change in pull request #1870:
URL: https://github.com/apache/iceberg/pull/1870#discussion_r536895473



##########
File path: core/src/main/java/org/apache/iceberg/hadoop/JdbcTableDao.java
##########
@@ -0,0 +1,128 @@
+/*
+ * 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.iceberg.hadoop;
+
+import java.sql.SQLException;
+import java.util.List;
+import org.apache.commons.dbutils.QueryRunner;
+import org.apache.commons.dbutils.handlers.BeanHandler;
+import org.apache.commons.dbutils.handlers.BeanListHandler;
+import org.apache.iceberg.catalog.Namespace;
+import org.apache.iceberg.catalog.TableIdentifier;
+import org.apache.iceberg.exceptions.NoSuchTableException;
+import org.apache.iceberg.relocated.com.google.common.collect.Lists;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+
+public class JdbcTableDao {
+  public static final String TABLES_TABLE_NAME = "iceberg_tables";
+  public static final String JDBC_CATALOG_TABLE_DDL =
+          "CREATE TABLE IF NOT EXISTS " + JdbcTableDao.TABLES_TABLE_NAME +
+                  "(catalogName VARCHAR(1255) NOT NULL," +
+                  "tableNamespace VARCHAR(1255) NOT NULL," +
+                  "tableName VARCHAR(1255) NOT NULL," +
+                  "metadataLocation VARCHAR(32768)," +
+                  "previousMetadataLocation VARCHAR(32768)," +
+                  "PRIMARY KEY (catalogName,tableNamespace,tableName)," +
+                  "FOREIGN KEY (catalogName, tableNamespace) REFERENCES " + 
JdbcNamespaceDao.NAMESPACES_TABLE_NAME +
+                  "(catalogName, namespace)" +
+                  ");";
+  private static final Logger LOG = 
LoggerFactory.getLogger(JdbcTableDao.class);
+  private final QueryRunner queryRunner;
+  private final String catalogName;
+
+
+  public JdbcTableDao(QueryRunner queryRunner, String catalogName) {
+    this.queryRunner = queryRunner;
+    this.catalogName = catalogName;
+  }
+
+  public boolean isExists(TableIdentifier tableIdentifier) {
+    try {
+      return this.get(tableIdentifier) != null;
+    } catch (SQLException throwables) {
+      return false;
+    }
+  }
+
+  public JdbcTable get(TableIdentifier tableIdentifier) throws SQLException {
+    return queryRunner.query("SELECT * FROM " + TABLES_TABLE_NAME + " " +
+                    "WHERE catalogName = ? AND tableNamespace = ? AND 
tableName = ? ",
+            new BeanHandler<>(JdbcTable.class),
+            catalogName, tableIdentifier.namespace().toString(), 
tableIdentifier.name());
+  }
+
+  public List<TableIdentifier> getAll(Namespace namespace) throws SQLException 
{
+    List<JdbcTable> tables = queryRunner.query("SELECT * FROM " + 
TABLES_TABLE_NAME + " " +
+                    "WHERE catalogName = ? AND tableNamespace = ?",
+            new BeanListHandler<>(JdbcTable.class), catalogName, 
namespace.toString());
+    List<TableIdentifier> results = Lists.newArrayList();
+    for (JdbcTable table : tables) {
+      results.add(table.toTableIdentifier());
+    }
+    return results;
+  }
+
+  public void update(TableIdentifier tableIdentifier, String 
oldMetadataLocation,
+                     String newMetadataLocation) throws SQLException {
+    queryRunner.update("UPDATE " + TABLES_TABLE_NAME + " SET metadataLocation 
= ? , previousMetadataLocation = ? " +
+                    "WHERE catalogName = ? AND tableNamespace = ? " +
+                    "AND tableName = ? ", newMetadataLocation,
+            oldMetadataLocation, catalogName, 
tableIdentifier.namespace().toString(), tableIdentifier.name());

Review comment:
       Looks like this doesn't yet implement an atomic swap of the old metadata 
location for the new one, so table updates would be unsafe because concurrent 
writers would clobber each other's commits. @kbendick, did your solution tackle 
that problem yet?




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