[GitHub] [iceberg] jackye1995 commented on a change in pull request #1849: API for supporting a TransactionalCatalog to enable multi-table transactions

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jackye1995 commented on a change in pull request #1849:
URL: https://github.com/apache/iceberg/pull/1849#discussion_r534663135



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File path: api/src/main/java/org/apache/iceberg/catalog/SupportsCatalogTransactions.java
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@@ -0,0 +1,137 @@
+/*
+ * 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.catalog;
+
+import java.util.Collections;
+import java.util.Set;
+
+/**
+ * Catalog methods for working with catalog-level transactions.
+ *
+ * <p>Catalog implementations are not required to support catalog-level transactional state.
+ * If they do, they may support one or more {@code IsolationLevel}s and one or more
+ * {@code LockingMode}s.
+ */
+public interface SupportsCatalogTransactions {
+
+  /**
+   * The level of isolation for a transaction.

Review comment:
       should there also be a level of of `READ_UNCOMMITTED`? This allows us to have a default with no transaction support in the `isolationLevels()` method below, and a default `DefaultTransactionalCatalog` implementation that can wrap any catalogs to support read uncommitted multi-table commits.

##########
File path: api/src/main/java/org/apache/iceberg/catalog/SupportsCatalogTransactions.java
##########
@@ -0,0 +1,137 @@
+/*
+ * 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.catalog;
+
+import java.util.Collections;
+import java.util.Set;
+
+/**
+ * Catalog methods for working with catalog-level transactions.
+ *
+ * <p>Catalog implementations are not required to support catalog-level transactional state.
+ * If they do, they may support one or more {@code IsolationLevel}s and one or more
+ * {@code LockingMode}s.
+ */
+public interface SupportsCatalogTransactions {
+
+  /**
+   * The level of isolation for a transaction.
+   */
+  enum IsolationLevel {
+
+    /**
+     * Only read committed data. Reading the same table multiple times
+     * may result in different committed reads for each read.
+     */
+    READ_COMMITTED,
+
+    /**
+     * Only read committed data. Reading the same table multiple times will
+     * result in the same view of those tables.

Review comment:
       I feel a bit confused since the definition here sound like snapshot isolation but the terminology is repeatable read, although I can see where this is coming from. It just does not match my understanding of these terms in sql server. Does it make more sense to just list out all the different combinations of isolation levels and lock modes as different isolation levels like sql server, so that we have the following levels:
   - read committed
   - read committed snapshot isolation
   - repeatable read
   - snapshot isolation
   - serializable




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