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/*
* 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.drill.exec.physical.impl.scan.file;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.apache.drill.common.exceptions.ExecutionSetupException;
import org.apache.drill.common.exceptions.UserException;
import org.apache.drill.common.expression.SchemaPath;
import org.apache.drill.exec.physical.impl.scan.RowBatchReader;
import org.apache.drill.exec.physical.impl.scan.framework.AbstractScanFramework;
import org.apache.drill.exec.physical.impl.scan.framework.ManagedReader;
import org.apache.drill.exec.physical.impl.scan.framework.SchemaNegotiator;
import org.apache.drill.exec.physical.impl.scan.framework.ShimBatchReader;
import org.apache.drill.exec.store.dfs.DrillFileSystem;
import org.apache.drill.exec.store.dfs.easy.FileWork;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapred.FileSplit;
/**
* Scan framework for a file that implements metadata columns (AKA "implicit"
* columns and partition columns.)
* <p>
* Framework iterators over file descriptions, creating readers at the
* moment they are needed. This allows simpler logic because, at the point of
* reader creation, we have a file system, context and so on.
*/
public abstract class BaseFileScanFramework<T extends BaseFileScanFramework.FileSchemaNegotiator>
extends AbstractScanFramework<T> {
static final org.slf4j.Logger logger = org.slf4j.LoggerFactory.getLogger(BaseFileScanFramework.class);
/**
* The file schema negotiator adds no behavior at present, but is
* created as a placeholder anticipating the need for file-specific
* behavior later. Readers are expected to use an instance of this
* class so that their code need not change later if/when we add new
* methods. For example, perhaps we want to specify an assumed block
* size for S3 files, or want to specify behavior if the file no longer
* exists. Those are out of scope of this first round of changes which
* focus on schema.
*/
public interface FileSchemaNegotiator extends SchemaNegotiator {
}
private final List<? extends FileWork> files;
private final Configuration fsConfig;
private List<FileSplit> spilts = new ArrayList<>();
private Iterator<FileSplit> splitIter;
private Path scanRootDir;
protected DrillFileSystem dfs;
private FileMetadataManager metadataManager;
public BaseFileScanFramework(List<SchemaPath> projection,
List<? extends FileWork> files,
Configuration fsConf) {
super(projection);
this.files = files;
this.fsConfig = fsConf;
}
/**
* Specify the selection root for a directory scan, if any.
* Used to populate partition columns.
* @param rootPath Hadoop file path for the directory
*/
public void setSelectionRoot(Path rootPath) {
this.scanRootDir = rootPath;
}
@Override
protected void configure() {
super.configure();
// Create the Drill file system.
try {
dfs = context.newFileSystem(fsConfig);
} catch (IOException e) {
throw UserException.dataReadError(e)
.addContext("Failed to create FileSystem")
.build(logger);
}
// Prepare the list of files. We need the list of paths up
// front to compute the maximum partition. Then, we need to
// iterate over the splits to create readers on demand.
List<Path> paths = new ArrayList<>();
for (FileWork work : files) {
Path path = dfs.makeQualified(work.getPath());
paths.add(path);
FileSplit split = new FileSplit(path, work.getStart(), work.getLength(), new String[]{""});
spilts.add(split);
}
splitIter = spilts.iterator();
// Create the metadata manager to handle file metadata columns
// (so-called implicit columns and partition columns.)
metadataManager = new FileMetadataManager(
context.getFragmentContext().getOptions(),
scanRootDir,
paths);
scanOrchestrator.withMetadata(metadataManager);
}
@Override
public RowBatchReader nextReader() {
// Create a reader on demand for the next split.
if (! splitIter.hasNext()) {
return null;
}
FileSplit split = splitIter.next();
// Alert the framework that a new file is starting.
startFile(split);
try {
// Create a per-framework reader wrapped in a standard
// "shim" reader. Allows app-specific readers to be very focused;
// the shim handles standard boilerplate.
return new ShimBatchReader<T>(this, newReader(split));
} catch (ExecutionSetupException e) {
throw UserException.executionError(e)
.addContext("File", split.getPath().toString())
.build(logger);
}
}
protected abstract ManagedReader<T> newReader(FileSplit split) throws ExecutionSetupException;
protected void startFile(FileSplit split) {
// Tell the metadata manager about the current file so it can
// populate the metadata columns, if requested.
metadataManager.startFile(split.getPath());
}
}
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