Github user magpierre commented on a diff in the pull request:
https://github.com/apache/drill/pull/451#discussion_r58943891
--- Diff:
contrib/storage-xml/src/main/java/org/apache/drill/exec/store/easy/xml/XMLRecordReader.java
---
@@ -0,0 +1,95 @@
+/**
+ * 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.store.easy.xml;
+
+import com.fasterxml.jackson.annotation.JsonInclude;
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+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.exception.OutOfMemoryException;
+import org.apache.drill.exec.ops.FragmentContext;
+import org.apache.drill.exec.ops.OperatorContext;
+import org.apache.drill.exec.physical.impl.OutputMutator;
+import org.apache.drill.exec.store.dfs.DrillFileSystem;
+import org.apache.drill.exec.store.easy.json.JSONRecordReader;
+import org.apache.hadoop.fs.FSDataInputStream;
+import org.apache.hadoop.fs.Path;
+import org.xml.sax.SAXException;
+import javax.xml.parsers.ParserConfigurationException;
+import javax.xml.parsers.SAXParser;
+import javax.xml.parsers.SAXParserFactory;
+import java.io.IOException;
+import java.util.List;
+
+
+public class XMLRecordReader extends JSONRecordReader {
+ private static final org.slf4j.Logger logger =
org.slf4j.LoggerFactory.getLogger(XMLRecordReader.class);
+ private XMLSaxParser handler;
+ private SAXParser xmlParser;
+ private JsonNode node;
+
+ public XMLRecordReader(FragmentContext fragmentContext, String
inputPath, DrillFileSystem fileSystem, List<SchemaPath> columns,
XMLFormatPlugin.XMLFormatConfig xmlConfig) throws OutOfMemoryException {
+ super(fragmentContext, inputPath, fileSystem, columns);
+ try {
+ FSDataInputStream fsStream = fileSystem.open(new
Path(inputPath));
+ SAXParserFactory saxParserFactory =
SAXParserFactory.newInstance();
+ xmlParser = saxParserFactory.newSAXParser();
+ handler = new XMLSaxParser();
+ handler.setRemoveNameSpace(!xmlConfig.getKeepPrefix());
+ xmlParser.parse(fsStream.getWrappedStream(), handler);
+ ObjectMapper mapper = new ObjectMapper();
+ node = mapper.valueToTree(handler.getVal());
--- End diff --
The XML parser is streaming based. Due to SAX which is a stateless parser
where each tag triggers a series of events and then drops the information, it
comes with a very little memory overhead. However, as noted I keep all parsed
objects in a stack since I need to link them. Due to the way the parsing works
the root of the document is really getting its children last, which means that
once parsed I have the whole document in memory but in JSON format so I will at
least not keep both a JSON document and an XML document in memory at the same
time. I've been considering storing state in files instead but I don't think it
would be performing well considering I need to revisit objects frequently. If
you have any suggestions such as memory mapped files that could spill down to
disk if large, it would be appreciated.
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