docs: Add documentation for accelerating Iceberg Parquet scans with Comet

common/src/main/java/org/apache/arrow/c/CometSchemaImporter.java → common/src/main/java/org/apache/arrow/c/AbstractCometSchemaImporter.java

@@ -24,12 +24,12 @@
 import org.apache.arrow.vector.types.pojo.Field;
 
 /** This is a simple wrapper around SchemaImporter to make it accessible from Java Arrow. */
-public class CometSchemaImporter {
+public abstract class AbstractCometSchemaImporter {
   private final BufferAllocator allocator;
   private final SchemaImporter importer;
   private final CDataDictionaryProvider provider = new CDataDictionaryProvider();
 
-  public CometSchemaImporter(BufferAllocator allocator) {
+  public AbstractCometSchemaImporter(BufferAllocator allocator) {
     this.allocator = allocator;
     this.importer = new SchemaImporter(allocator);
   }

common/src/main/java/org/apache/comet/CometSchemaImporter.java

@@ -0,0 +1,30 @@
+/*
+ * 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.comet;
+
+import org.apache.arrow.c.*;
+import org.apache.arrow.memory.BufferAllocator;
+
+/** This is a simple wrapper around SchemaImporter to make it accessible from Java Arrow. */
+public class CometSchemaImporter extends AbstractCometSchemaImporter {
+  public CometSchemaImporter(BufferAllocator allocator) {
+    super(allocator);
+  }
+}

common/src/main/java/org/apache/comet/parquet/BatchReader.java

@@ -34,7 +34,6 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.commons.lang3.tuple.Pair;
@@ -65,6 +64,7 @@
 import org.apache.spark.util.AccumulatorV2;
 
 import org.apache.comet.CometConf;
+import org.apache.comet.CometSchemaImporter;
 import org.apache.comet.shims.ShimBatchReader;
 import org.apache.comet.shims.ShimFileFormat;
 import org.apache.comet.vector.CometVector;

common/src/main/java/org/apache/comet/parquet/ColumnReader.java

@@ -27,7 +27,6 @@
 
 import org.apache.arrow.c.ArrowArray;
 import org.apache.arrow.c.ArrowSchema;
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.arrow.vector.FieldVector;
@@ -44,6 +43,7 @@
 import org.apache.spark.sql.types.DataType;
 
 import org.apache.comet.CometConf;
+import org.apache.comet.CometSchemaImporter;
 import org.apache.comet.vector.CometDecodedVector;
 import org.apache.comet.vector.CometDictionary;
 import org.apache.comet.vector.CometDictionaryVector;

common/src/main/java/org/apache/comet/parquet/LazyColumnReader.java

@@ -21,11 +21,11 @@
 
 import java.io.IOException;
 
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.parquet.column.ColumnDescriptor;
 import org.apache.parquet.column.page.PageReader;
 import org.apache.spark.sql.types.DataType;
 
+import org.apache.comet.CometSchemaImporter;
 import org.apache.comet.vector.CometLazyVector;
 import org.apache.comet.vector.CometVector;
 

common/src/main/java/org/apache/comet/parquet/NativeBatchReader.java

@@ -36,7 +36,6 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.arrow.vector.ipc.WriteChannel;
@@ -71,6 +70,7 @@
 import org.apache.spark.util.AccumulatorV2;
 
 import org.apache.comet.CometConf;
+import org.apache.comet.CometSchemaImporter;
 import org.apache.comet.shims.ShimBatchReader;
 import org.apache.comet.shims.ShimFileFormat;
 import org.apache.comet.vector.CometVector;

common/src/main/java/org/apache/comet/parquet/NativeColumnReader.java

@@ -24,13 +24,13 @@
 
 import org.apache.arrow.c.ArrowArray;
 import org.apache.arrow.c.ArrowSchema;
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.arrow.memory.BufferAllocator;
 import org.apache.arrow.memory.RootAllocator;
 import org.apache.parquet.column.ColumnDescriptor;
 import org.apache.parquet.schema.Type;
 import org.apache.spark.sql.types.DataType;
 
+import org.apache.comet.CometSchemaImporter;
 import org.apache.comet.vector.*;
 
 // TODO: extend ColumnReader instead of AbstractColumnReader to reduce code duplication

common/src/main/java/org/apache/comet/parquet/SupportsComet.java

@@ -19,6 +19,7 @@
 
 package org.apache.comet.parquet;
 
+/** This is implemented in Apache Iceberg */
 public interface SupportsComet {
   boolean isCometEnabled();
 }

common/src/main/java/org/apache/comet/parquet/Utils.java

@@ -19,13 +19,16 @@
 
 package org.apache.comet.parquet;
 
-import org.apache.arrow.c.CometSchemaImporter;
 import org.apache.parquet.column.ColumnDescriptor;
 import org.apache.parquet.schema.LogicalTypeAnnotation;
 import org.apache.parquet.schema.PrimitiveType;
 import org.apache.spark.sql.types.*;
 
+import org.apache.comet.CometSchemaImporter;
+
 public class Utils {
+
+  /** This method is called from Apache Iceberg. */
   public static ColumnReader getColumnReader(
       DataType type,
       ColumnDescriptor descriptor,

docs/source/user-guide/datasources.md

@@ -19,29 +19,36 @@
 
 # Supported Spark Data Sources
 
-## Parquet
+## File Formats
+
+### Parquet
 
 When `spark.comet.scan.enabled` is enabled, Parquet scans will be performed natively by Comet if all data types
 in the schema are supported. When this option is not enabled, the scan will fall back to Spark. In this case,
 enabling `spark.comet.convert.parquet.enabled` will immediately convert the data into Arrow format, allowing native 
 execution to happen after that, but the process may not be efficient.
 
-## CSV
+### CSV
 
 Comet does not provide native CSV scan, but when `spark.comet.convert.csv.enabled` is enabled, data is immediately
 converted into Arrow format, allowing native execution to happen after that.
 
-## JSON
+### JSON
 
 Comet does not provide native JSON scan, but when `spark.comet.convert.json.enabled` is enabled, data is immediately
 converted into Arrow format, allowing native execution to happen after that.
 
-# Supported Storages
+## Data Catalogs
+
+### Apache Iceberg
+
+See the dedicated [Comet and Iceberg Guide](iceberg.md).
+
+## Supported Storages
 
-## Local
-In progress
+Comet supports most standard storage systems, such as local file system and object storage.
 
-## HDFS
+### HDFS
 
 Apache DataFusion Comet native reader seamlessly scans files from remote HDFS for [supported formats](#supported-spark-data-sources)
 

docs/source/user-guide/iceberg.md

@@ -0,0 +1,147 @@
+<!---
+  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.
+-->
+
+# Accelerating Apache Iceberg Parquet Scans using Comet (Experimental)
+
+**Note: Iceberg integration is a work-in-progress. It is currently necessary to build Iceberg from
+source rather than using available artifacts in Maven**
+
+## Build Comet
+
+Run a Maven install so that we can compile Iceberg against latest Comet:
+
+```shell
+mvn install -DskipTests
+```
+
+Build the release JAR to be used from Spark:
+
+```shell
+make release
+```
+
+Set `COMET_JAR` env var:
+
+```shell
+export COMET_JAR=`pwd`/spark/target/comet-spark-spark3.5_2.12-0.9.0-SNAPSHOT.jar
+```
+
+## Build Iceberg
+
+Clone the Iceberg repository.
+
+```shell
+git clone git@github.com:apache/iceberg.git
+```
+
+It will be necessary to make some small changes to Iceberg:
+
+- Update Gradle files to change Comet version to `0.9.0-SNAPSHOT`.
+- Replace `import org.apache.comet.shaded.arrow.c.CometSchemaImporter;` with `import org.apache.comet.CometSchemaImporter;`
+- Modify `SparkBatchQueryScan` so that it implements the `SupportsComet` interface
+- Stop shading Parquet by commenting out the following lines in the iceberg-spark build:
+
+```
+//    relocate 'org.apache.parquet', 'org.apache.iceberg.shaded.org.apache.parquet'
+//    relocate 'shaded.parquet', 'org.apache.iceberg.shaded.org.apache.parquet.shaded'
+```
+
+Perform a clean build
+
+```shell
+./gradlew clean
+./gradlew build -x test -x integrationTest
+```
+
+## Test
+
+Set `ICEBERG_JAR` environment variable.
+
+```shell
+export ICEBERG_JAR=`pwd`/spark/v3.5/spark-runtime/build/libs/iceberg-spark-runtime-3.5_2.12-1.10.0-SNAPSHOT.jar
+```
+
+Launch Spark Shell:
+
+```shell
+$SPARK_HOME/bin/spark-shell \
+    --jars $COMET_JAR,$ICEBERG_JAR \
+    --conf spark.driver.extraClassPath=$COMET_JAR,$ICEBERG_JAR \
+    --conf spark.executor.extraClassPath=$COMET_JAR,$ICEBERG_JAR \
+    --conf spark.sql.extensions=org.apache.iceberg.spark.extensions.IcebergSparkSessionExtensions \
+    --conf spark.sql.catalog.spark_catalog=org.apache.iceberg.spark.SparkCatalog \
+    --conf spark.sql.catalog.spark_catalog.type=hadoop \
+    --conf spark.sql.catalog.spark_catalog.warehouse=/tmp/warehouse \
+    --conf spark.plugins=org.apache.spark.CometPlugin \
+    --conf spark.shuffle.manager=org.apache.spark.sql.comet.execution.shuffle.CometShuffleManager \
+    --conf spark.sql.iceberg.parquet.reader-type=COMET \
+    --conf spark.comet.explainFallback.enabled=true \
+    --conf spark.memory.offHeap.enabled=true \
+    --conf spark.memory.offHeap.size=16g
+```
+
+Create an Iceberg table. Note that Comet will not accelerate this part.
+
+```
+scala> spark.sql(s"CREATE TABLE IF NOT EXISTS t1 (c0 INT, c1 STRING) USING iceberg")
+scala> spark.sql(s"INSERT INTO t1 VALUES ${(0 until 10000).map(i => (i, i)).mkString(",")}")
+```
+
+Comet should now be able to accelerate reading the table:
+
+```
+scala> spark.sql(s"SELECT * from t1").show()
+```
+
+This should produce the following output:
+
+```
+scala> spark.sql(s"SELECT * from t1").show()
+25/04/28 07:29:37 INFO core/src/lib.rs: Comet native library version 0.9.0 initialized
+25/04/28 07:29:37 WARN CometSparkSessionExtensions$CometExecRule: Comet cannot execute some parts of this plan natively (set spark.comet.explainFallback.enabled=false to disable this logging):
+ CollectLimit [COMET: CollectLimit is not supported]
++-  Project [COMET: toprettystring is not supported]
+   +- CometScanWrapper
+
++---+---+
+| c0| c1|
++---+---+
+|  0|  0|
+|  1|  1|
+|  2|  2|
+|  3|  3|
+|  4|  4|
+|  5|  5|
+|  6|  6|
+|  7|  7|
+|  8|  8|
+|  9|  9|
+| 10| 10|
+| 11| 11|
+| 12| 12|
+| 13| 13|
+| 14| 14|
+| 15| 15|
+| 16| 16|
+| 17| 17|
+| 18| 18|
+| 19| 19|
++---+---+
+only showing top 20 rows
+```

spark/src/main/scala/org/apache/comet/CometSparkSessionExtensions.scala

@@ -230,8 +230,11 @@ class CometSparkSessionExtensions
           withInfo(scanExec, fallbackReasons.mkString(", "))
         }
 
-      case _ =>
-        withInfo(scanExec, "Comet Scan only supports Parquet and Iceberg Parquet file formats")
+      case other =>
+        withInfo(
+          scanExec,
+          s"Unsupported scan: ${other.getClass.getName}. " +
+            "Comet Scan only supports Parquet and Iceberg Parquet file formats")
     }
   }