[GitHub] [incubator-pinot] mayankshriv commented on a change in pull request #4432: #4401 Reuse a ThreadLocal byte[] when reading String elements from the variable length value reader.

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mayankshriv commented on a change in pull request #4432: #4401 Reuse a ThreadLocal byte[] when reading String elements from the variable length value reader.
URL: https://github.com/apache/incubator-pinot/pull/4432#discussion_r303524029
 
 

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 File path: pinot-core/src/main/java/org/apache/pinot/core/io/util/VarLengthBytesValueReaderWriter.java
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 @@ -204,7 +223,26 @@ public double getDouble(int index) {
 
   @Override
   public String getUnpaddedString(int index, int numBytesPerValue, byte paddingByte, byte[] buffer) {
-    return StringUtil.decodeUtf8(getBytes(index, numBytesPerValue, buffer));
+    // Read the offset of the byte array first and then read the actual byte array.
+    int offset = _dataBuffer.getInt(_dataSectionStartOffSet + Integer.BYTES * index);
+
+    // To get the length of the byte array, we use the next byte array offset.
+    int length = _dataBuffer.getInt(_dataSectionStartOffSet + Integer.BYTES * (index + 1)) - offset;
+
+    byte[] b;
+    if (buffer != null && buffer.length >= length) {
+      b = buffer;
+    } else {
+      // Check if the current instance of ThreadLocal buffer is big enough. If not, resize it to double the size.
+      b = _reusableBytes.get();
+      if (b.length < length) {
+        b = new byte[nextPowerOf2(length)];
 
 Review comment:
   Do we allow arbitary length strings? IIRC @Jackie-Jiang had put a max string length limit? If so, we could cap this allocation to that limit as well.

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