[GitHub] [iotdb] liutaohua commented on a change in pull request #3218: [WIP] Dictionary encoding for TEXT

[GitBox <gi...@apache.org>]

liutaohua commented on a change in pull request #3218:
URL: https://github.com/apache/iotdb/pull/3218#discussion_r637868568



##########
File path: antlr/src/main/antlr4/org/apache/iotdb/db/qp/sql/SqlBase.g4
##########
@@ -695,7 +695,7 @@ dateExpression
     ;
 
 encoding
-    : PLAIN | PLAIN_DICTIONARY | RLE | DIFF | TS_2DIFF | GORILLA | REGULAR
+    : PLAIN | PLAIN_DICTIONARY | RLE | DIFF | TS_2DIFF | GORILLA | REGULAR | DICTIONARY

Review comment:
       I suggest renaming the original `PLAIN_DICTIONARY` as `DICTIONARY`, and modify the relevant documents, including `Format.md` and so on...

##########
File path: client-cpp/src/main/Session.h
##########
@@ -112,7 +112,8 @@ namespace TSEncoding {
         BITMAP = 5,
         GORILLA_V1 = 6,
         REGULAR = 7,
-        GORILLA = 8
+        GORILLA = 8,
+        DICTIONARY = 9

Review comment:
       reuse the number of `PLAIN_DICTIONARY`

##########
File path: client-py/iotdb/utils/IoTDBConstants.py
##########
@@ -40,6 +40,7 @@ class TSEncoding(Enum):
     GORILLA_V1 = 6
     REGULAR = 7
     GORILLA = 8
+    DICTIONARY = 9

Review comment:
       same

##########
File path: tsfile/src/main/java/org/apache/iotdb/tsfile/encoding/encoder/DictionaryEncoder.java
##########
@@ -0,0 +1,113 @@
+/*
+ * 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.iotdb.tsfile.encoding.encoder;
+
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.utils.Binary;
+import org.apache.iotdb.tsfile.utils.ReadWriteForEncodingUtils;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+/**
+ * An encoder implementing dictionary encoding.
+ *
+ * <pre>Encoding format: {@code
+ * <map> <indexes>
+ * <map> := <map length> <map data>
+ * <map data> := [<entry size><entry data>]...
+ * <indexes> := [<index>]...
+ * }</pre>
+ */
+public class DictionaryEncoder extends Encoder {
+  private static final Logger logger = LoggerFactory.getLogger(DictionaryEncoder.class);
+
+  private HashMap<Binary, Integer> valueToCode;

Review comment:
       rename to entryIndex

##########
File path: tsfile/src/main/java/org/apache/iotdb/tsfile/encoding/encoder/DictionaryEncoder.java
##########
@@ -0,0 +1,113 @@
+/*
+ * 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.iotdb.tsfile.encoding.encoder;
+
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.utils.Binary;
+import org.apache.iotdb.tsfile.utils.ReadWriteForEncodingUtils;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+
+/**
+ * An encoder implementing dictionary encoding.
+ *
+ * <pre>Encoding format: {@code
+ * <map> <indexes>
+ * <map> := <map length> <map data>
+ * <map data> := [<entry size><entry data>]...
+ * <indexes> := [<index>]...
+ * }</pre>
+ */
+public class DictionaryEncoder extends Encoder {
+  private static final Logger logger = LoggerFactory.getLogger(DictionaryEncoder.class);
+
+  private HashMap<Binary, Integer> valueToCode;
+  private List<Binary> map;

Review comment:
       rename to IndexEntry

##########
File path: tsfile/src/main/java/org/apache/iotdb/tsfile/encoding/decoder/DictionaryDecoder.java
##########
@@ -0,0 +1,86 @@
+/*
+ * 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.iotdb.tsfile.encoding.decoder;
+
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.utils.Binary;
+import org.apache.iotdb.tsfile.utils.ReadWriteForEncodingUtils;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DictionaryDecoder extends Decoder {
+  private static final Logger logger = LoggerFactory.getLogger(DictionaryDecoder.class);
+
+  private List<Binary> map;

Review comment:
       rename to `indexEntry`

##########
File path: tsfile/src/main/java/org/apache/iotdb/tsfile/encoding/decoder/DictionaryDecoder.java
##########
@@ -0,0 +1,86 @@
+/*
+ * 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.iotdb.tsfile.encoding.decoder;
+
+import org.apache.iotdb.tsfile.file.metadata.enums.TSEncoding;
+import org.apache.iotdb.tsfile.utils.Binary;
+import org.apache.iotdb.tsfile.utils.ReadWriteForEncodingUtils;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.io.IOException;
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.List;
+
+public class DictionaryDecoder extends Decoder {
+  private static final Logger logger = LoggerFactory.getLogger(DictionaryDecoder.class);
+
+  private List<Binary> map;
+  private IntRleDecoder valueDecoder;
+
+  public DictionaryDecoder() {
+    super(TSEncoding.DICTIONARY);
+
+    valueDecoder = new IntRleDecoder();
+  }
+
+  @Override
+  public boolean hasNext(ByteBuffer buffer) {
+    if (map == null) {
+      initMap(buffer);
+    }
+
+    try {
+      return valueDecoder.hasNext(buffer);
+    } catch (IOException e) {
+      logger.error("tsfile-decoding DictionaryDecoder: error occurs when decoding", e);
+    }
+
+    return false;
+  }
+
+  @Override
+  public Binary readBinary(ByteBuffer buffer) {
+    if (map == null) {
+      initMap(buffer);
+    }
+    int code = valueDecoder.readInt(buffer);
+    return map.get(code);
+  }
+
+  private void initMap(ByteBuffer buffer) {
+    map = new ArrayList<>();
+    int length = ReadWriteForEncodingUtils.readVarInt(buffer);

Review comment:
       initialize the array with a fixed length to avoid redundant copies




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