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Posted to issues@iceberg.apache.org by GitBox <gi...@apache.org> on 2020/04/15 19:09:00 UTC
[GitHub] [incubator-iceberg] rdblue opened a new pull request #924: Add void
transform that always produces null
rdblue opened a new pull request #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924
This adds a new transform function, `void`, that always produces a null value. Because `void` and `null` are Java keywords, the `PartitionSpecBuilder` is configured using `alwaysNull`.
The purpose of this transform is to be a stand-in for partition transforms that are removed from a spec. In the v1 table format, IDs for partition fields are not tracked by `PartitionSpec`. Instead, they are assigned starting at 1000 for each spec. Because tables may have more than one spec, manifest files could have incompatible partition field structs. This is not a problem for job planning because each manifest is read independently, but it can break metadata tables that show a union of all manifest data files or entries.
The `void` transform can be used to avoid a problem with ID assignment. If a table has two partition fields, `1000: categorical string, 1001: ts_day int`, then removing the `categorical` partition will create a new partition spec with `1000: ts_day int`. That would create a problem in the metadata tables. Instead of deleting the categorical partition, it should be replaced with a `void` partition to keep the IDs aligned: `1000: always_null string, 1001: ts_day int`.
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[GitHub] [incubator-iceberg] danielcweeks commented on issue #924: Add void
transform that always produces null
Posted by GitBox <gi...@apache.org>.
danielcweeks commented on issue #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924#issuecomment-614238463
One minor comment, but +1 (pending checks)
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[GitHub] [incubator-iceberg] danielcweeks commented on a change in pull
request #924: Add void transform that always produces null
Posted by GitBox <gi...@apache.org>.
danielcweeks commented on a change in pull request #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924#discussion_r409084413
##########
File path: api/src/main/java/org/apache/iceberg/transforms/VoidTransform.java
##########
@@ -0,0 +1,76 @@
+/*
+ * 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.transforms;
+
+import java.io.ObjectStreamException;
+import org.apache.iceberg.expressions.BoundPredicate;
+import org.apache.iceberg.expressions.UnboundPredicate;
+import org.apache.iceberg.types.Type;
+
+class VoidTransform<S> implements Transform<S, Void> {
+ private static final VoidTransform<Object> INSTANCE = new VoidTransform<>();
+
+ @SuppressWarnings("unchecked")
+ static <T> VoidTransform<T> get() {
+ return (VoidTransform<T>) INSTANCE;
+ }
+
+ private VoidTransform() {
+ }
+
+ @Override
+ public Void apply(Object value) {
+ return null;
+ }
+
+ @Override
+ public boolean canTransform(Type type) {
+ return true;
+ }
+
+ @Override
+ public Type getResultType(Type sourceType) {
+ return sourceType;
+ }
+
+ @Override
+ public UnboundPredicate<Void> projectStrict(String name, BoundPredicate<S> predicate) {
+ return null;
+ }
+
+ @Override
+ public UnboundPredicate<Void> project(String name, BoundPredicate<S> predicate) {
+ return null;
+ }
+
+ @Override
+ public String toHumanString(Void value) {
+ return "null";
+ }
+
+ @Override
+ public String toString() {
+ return "void";
+ }
Review comment:
Minor nit here to think about . . . we seem to be using both `void` and `null`. Would it make more sense to just consistently use `void` as it seems to better indicate there there is no expected value?
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[GitHub] [incubator-iceberg] rdblue commented on issue #924: Add void
transform that always produces null
Posted by GitBox <gi...@apache.org>.
rdblue commented on issue #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924#issuecomment-614228381
@jun-he, FYI. This is related to #922. Instead of deleting partitions in v1, we can replace them with the `void` transform.
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[GitHub] [incubator-iceberg] rdblue commented on a change in pull request
#924: Add void transform that always produces null
Posted by GitBox <gi...@apache.org>.
rdblue commented on a change in pull request #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924#discussion_r409093584
##########
File path: api/src/main/java/org/apache/iceberg/transforms/VoidTransform.java
##########
@@ -0,0 +1,76 @@
+/*
+ * 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.transforms;
+
+import java.io.ObjectStreamException;
+import org.apache.iceberg.expressions.BoundPredicate;
+import org.apache.iceberg.expressions.UnboundPredicate;
+import org.apache.iceberg.types.Type;
+
+class VoidTransform<S> implements Transform<S, Void> {
+ private static final VoidTransform<Object> INSTANCE = new VoidTransform<>();
+
+ @SuppressWarnings("unchecked")
+ static <T> VoidTransform<T> get() {
+ return (VoidTransform<T>) INSTANCE;
+ }
+
+ private VoidTransform() {
+ }
+
+ @Override
+ public Void apply(Object value) {
+ return null;
+ }
+
+ @Override
+ public boolean canTransform(Type type) {
+ return true;
+ }
+
+ @Override
+ public Type getResultType(Type sourceType) {
+ return sourceType;
+ }
+
+ @Override
+ public UnboundPredicate<Void> projectStrict(String name, BoundPredicate<S> predicate) {
+ return null;
+ }
+
+ @Override
+ public UnboundPredicate<Void> project(String name, BoundPredicate<S> predicate) {
+ return null;
+ }
+
+ @Override
+ public String toHumanString(Void value) {
+ return "null";
+ }
+
+ @Override
+ public String toString() {
+ return "void";
+ }
Review comment:
Null is the human-readable string for the value produced by the transform. Void is the name of the transform. I considered naming it something like `always_null` but `void` seemed shorter and less error prone (was that alwaysNull or always-null?)
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[GitHub] [incubator-iceberg] rdblue merged pull request #924: Add void
transform that always produces null
Posted by GitBox <gi...@apache.org>.
rdblue merged pull request #924: Add void transform that always produces null
URL: https://github.com/apache/incubator-iceberg/pull/924
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