Jackie-Jiang commented on code in PR #10044:
URL: https://github.com/apache/pinot/pull/10044#discussion_r1061013153


##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {

Review Comment:
   (Code format) Please fix the indentation



##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {
+    }
+
+    private static int mismatch(PinotDataBuffer dataBuffer, long startOffset, 
int length, ByteBuffer buffer) {
+        boolean littleEndian = dataBuffer.order() == ByteOrder.LITTLE_ENDIAN;
+        if (littleEndian) {
+            buffer.order(ByteOrder.LITTLE_ENDIAN);
+        }
+        int limit = Math.min(length, buffer.limit());
+        int loopBound = limit & ~0x3F;

Review Comment:
   Why `~0x3F` instead of `~7`?



##########
pinot-segment-local/src/test/java/org/apache/pinot/segment/local/segment/index/readerwriter/ValueReaderComparisonTest.java:
##########
@@ -0,0 +1,330 @@
+/**
+ * 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.pinot.segment.local.segment.index.readerwriter;
+
+import java.io.IOException;
+import java.nio.ByteOrder;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.UUID;
+import java.util.concurrent.ThreadLocalRandom;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+import org.apache.commons.lang3.tuple.Pair;
+import org.apache.pinot.segment.local.io.util.FixedByteValueReaderWriter;
+import org.apache.pinot.segment.local.io.util.ValueReader;
+import org.apache.pinot.segment.local.io.util.VarLengthValueReader;
+import org.apache.pinot.segment.local.io.util.VarLengthValueWriter;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+import org.testng.annotations.DataProvider;
+import org.testng.annotations.Test;
+
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
+
+public class ValueReaderComparisonTest {
+    @DataProvider
+    public static Object[] text() {

Review Comment:
   (Code format) Please fix the indentation



##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {
+    }
+
+    private static int mismatch(PinotDataBuffer dataBuffer, long startOffset, 
int length, ByteBuffer buffer) {
+        boolean littleEndian = dataBuffer.order() == ByteOrder.LITTLE_ENDIAN;
+        if (littleEndian) {
+            buffer.order(ByteOrder.LITTLE_ENDIAN);
+        }
+        int limit = Math.min(length, buffer.limit());
+        int loopBound = limit & ~0x3F;
+        int i = 0;
+        for (; i < loopBound; i += 8) {
+            long ours = dataBuffer.getLong(startOffset + i);
+            long theirs = buffer.getLong(i);
+            if (ours != theirs) {
+                long difference = ours ^ theirs;
+                return i + ((littleEndian
+                        ? Long.numberOfTrailingZeros(difference)
+                        : Long.numberOfLeadingZeros(difference)) >>> 3);
+            }
+        }
+        for (; i < limit; i++) {
+            byte ours = dataBuffer.getByte(startOffset + i);
+            byte theirs = buffer.get(i);
+            if (ours != theirs) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    static int compareUtf8Bytes(PinotDataBuffer dataBuffer, long startOffset, 
int length, boolean padded,
+                           byte[] bytes) {
+        // can use MethodHandles.byteArrayViewVarHandle here after dropping 
JDK8
+        ByteBuffer buffer = ByteBuffer.wrap(bytes);
+        int mismatchPosition = mismatch(dataBuffer, startOffset, length, 
buffer);
+        if (mismatchPosition == -1) {
+            // need to figure out whether the unpadded string is longer than 
the parameter or not
+            if (padded && bytes.length < length) {
+                if (bytes.length == 0) {
+                    // just need nonzero first byte
+                    return dataBuffer.getByte(startOffset) == 0 ? 0 : 1;
+                } else if (bytes[bytes.length - 1] == 0) {
+                    // we can't store zero padding, but can have it in 
parameters, check the last byte
+                    return dataBuffer.getByte(startOffset + bytes.length - 1) 
== 0 ? -1 : 0;
+                } else {
+                    // check if the stored string continues beyond the length 
of the parameter
+                    return dataBuffer.getByte(startOffset + bytes.length) == 0 
? 0 : 1;
+                }
+            } else {
+                // then we know the length precisely or know that the 
parameter is at least as long as we can store
+                return length - bytes.length;
+            }
+        }
+        byte ourByte = dataBuffer.getByte(startOffset + mismatchPosition);
+        if (ourByte == 0) {
+            // then we are storing the empty string
+            return -1;
+        }
+        byte theirByte = bytes[mismatchPosition];
+        if (theirByte == 0) {
+            return 1;
+        }

Review Comment:
   I don't think we need these special handling since they are not very common 
case. We may change `first > 0` to `first >= 0` to handle the 0 byte in 
`compareUtf8()`



##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {
+    }
+
+    private static int mismatch(PinotDataBuffer dataBuffer, long startOffset, 
int length, ByteBuffer buffer) {
+        boolean littleEndian = dataBuffer.order() == ByteOrder.LITTLE_ENDIAN;
+        if (littleEndian) {
+            buffer.order(ByteOrder.LITTLE_ENDIAN);
+        }
+        int limit = Math.min(length, buffer.limit());
+        int loopBound = limit & ~0x3F;
+        int i = 0;
+        for (; i < loopBound; i += 8) {
+            long ours = dataBuffer.getLong(startOffset + i);
+            long theirs = buffer.getLong(i);
+            if (ours != theirs) {
+                long difference = ours ^ theirs;
+                return i + ((littleEndian
+                        ? Long.numberOfTrailingZeros(difference)
+                        : Long.numberOfLeadingZeros(difference)) >>> 3);
+            }
+        }
+        for (; i < limit; i++) {
+            byte ours = dataBuffer.getByte(startOffset + i);
+            byte theirs = buffer.get(i);
+            if (ours != theirs) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    static int compareUtf8Bytes(PinotDataBuffer dataBuffer, long startOffset, 
int length, boolean padded,
+                           byte[] bytes) {
+        // can use MethodHandles.byteArrayViewVarHandle here after dropping 
JDK8
+        ByteBuffer buffer = ByteBuffer.wrap(bytes);
+        int mismatchPosition = mismatch(dataBuffer, startOffset, length, 
buffer);
+        if (mismatchPosition == -1) {
+            // need to figure out whether the unpadded string is longer than 
the parameter or not
+            if (padded && bytes.length < length) {
+                if (bytes.length == 0) {
+                    // just need nonzero first byte
+                    return dataBuffer.getByte(startOffset) == 0 ? 0 : 1;
+                } else if (bytes[bytes.length - 1] == 0) {
+                    // we can't store zero padding, but can have it in 
parameters, check the last byte
+                    return dataBuffer.getByte(startOffset + bytes.length - 1) 
== 0 ? -1 : 0;
+                } else {
+                    // check if the stored string continues beyond the length 
of the parameter
+                    return dataBuffer.getByte(startOffset + bytes.length) == 0 
? 0 : 1;
+                }
+            } else {
+                // then we know the length precisely or know that the 
parameter is at least as long as we can store
+                return length - bytes.length;
+            }
+        }
+        byte ourByte = dataBuffer.getByte(startOffset + mismatchPosition);
+        if (ourByte == 0) {
+            // then we are storing the empty string
+            return -1;
+        }
+        byte theirByte = bytes[mismatchPosition];
+        if (theirByte == 0) {
+            return 1;
+        }
+        // we know the position of the mismatch but need to do utf8 decoding 
before comparison
+        // to respect collation rules
+        return compareUtf8(dataBuffer, startOffset, buffer, mismatchPosition);
+    }
+
+    private static int compareUtf8(PinotDataBuffer ourBuffer, long 
ourStartOffset,
+                           ByteBuffer theirBuffer, int mismatchPosition) {
+        char ours1 = '?';
+        char ours2 = '?';
+        char theirs1 = '?';
+        char theirs2 = '?';
+
+        // 1. seek backwards from mismatch position in each buffer to find 
start of each utf8 sequence
+        long ourPosition = ourStartOffset + mismatchPosition;
+        while (ourPosition > ourStartOffset && 
isUtf8Continuation(ourBuffer.getByte(ourPosition))) {

Review Comment:
   The boundary check is redundant. We can also move both our and their 
position together for better performance



##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {
+    }
+
+    private static int mismatch(PinotDataBuffer dataBuffer, long startOffset, 
int length, ByteBuffer buffer) {
+        boolean littleEndian = dataBuffer.order() == ByteOrder.LITTLE_ENDIAN;
+        if (littleEndian) {
+            buffer.order(ByteOrder.LITTLE_ENDIAN);
+        }
+        int limit = Math.min(length, buffer.limit());
+        int loopBound = limit & ~0x3F;
+        int i = 0;
+        for (; i < loopBound; i += 8) {
+            long ours = dataBuffer.getLong(startOffset + i);
+            long theirs = buffer.getLong(i);
+            if (ours != theirs) {
+                long difference = ours ^ theirs;
+                return i + ((littleEndian
+                        ? Long.numberOfTrailingZeros(difference)
+                        : Long.numberOfLeadingZeros(difference)) >>> 3);
+            }
+        }
+        for (; i < limit; i++) {
+            byte ours = dataBuffer.getByte(startOffset + i);
+            byte theirs = buffer.get(i);
+            if (ours != theirs) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    static int compareUtf8Bytes(PinotDataBuffer dataBuffer, long startOffset, 
int length, boolean padded,
+                           byte[] bytes) {
+        // can use MethodHandles.byteArrayViewVarHandle here after dropping 
JDK8
+        ByteBuffer buffer = ByteBuffer.wrap(bytes);
+        int mismatchPosition = mismatch(dataBuffer, startOffset, length, 
buffer);
+        if (mismatchPosition == -1) {
+            // need to figure out whether the unpadded string is longer than 
the parameter or not
+            if (padded && bytes.length < length) {
+                if (bytes.length == 0) {
+                    // just need nonzero first byte
+                    return dataBuffer.getByte(startOffset) == 0 ? 0 : 1;
+                } else if (bytes[bytes.length - 1] == 0) {
+                    // we can't store zero padding, but can have it in 
parameters, check the last byte
+                    return dataBuffer.getByte(startOffset + bytes.length - 1) 
== 0 ? -1 : 0;
+                } else {
+                    // check if the stored string continues beyond the length 
of the parameter
+                    return dataBuffer.getByte(startOffset + bytes.length) == 0 
? 0 : 1;
+                }
+            } else {
+                // then we know the length precisely or know that the 
parameter is at least as long as we can store
+                return length - bytes.length;
+            }
+        }
+        byte ourByte = dataBuffer.getByte(startOffset + mismatchPosition);
+        if (ourByte == 0) {
+            // then we are storing the empty string
+            return -1;
+        }
+        byte theirByte = bytes[mismatchPosition];
+        if (theirByte == 0) {
+            return 1;
+        }
+        // we know the position of the mismatch but need to do utf8 decoding 
before comparison
+        // to respect collation rules
+        return compareUtf8(dataBuffer, startOffset, buffer, mismatchPosition);
+    }
+
+    private static int compareUtf8(PinotDataBuffer ourBuffer, long 
ourStartOffset,
+                           ByteBuffer theirBuffer, int mismatchPosition) {
+        char ours1 = '?';
+        char ours2 = '?';
+        char theirs1 = '?';
+        char theirs2 = '?';
+
+        // 1. seek backwards from mismatch position in each buffer to find 
start of each utf8 sequence
+        long ourPosition = ourStartOffset + mismatchPosition;
+        while (ourPosition > ourStartOffset && 
isUtf8Continuation(ourBuffer.getByte(ourPosition))) {
+            ourPosition--;
+        }
+        int theirPosition = mismatchPosition;
+        while (theirPosition > 0 && 
isUtf8Continuation(theirBuffer.get(theirPosition))) {
+            theirPosition--;
+        }
+        // 2. decode to get the 1 or 2 characters containing where the 
mismatch lies
+        {
+            byte first = ourBuffer.getByte(ourPosition);
+            int control = first & 0xF0;
+            if (first > 0) {
+                ours1 = (char) (first & 0xFF);
+            } else if (control < 0xE0) {
+                ours1 = decode(first, ourBuffer.getByte(ourPosition + 1));
+            } else if (control == 0xE0) {
+                ours1 = decode(first, ourBuffer.getByte(ourPosition + 1),
+                        ourBuffer.getByte(ourPosition + 2));
+            } else {
+                int codepoint = decode(first, ourBuffer.getByte(ourPosition + 
1),
+                        ourBuffer.getByte(ourPosition + 2), 
ourBuffer.getByte(ourPosition + 3));
+                if (Character.isValidCodePoint(codepoint)) {

Review Comment:
   Does the logic handle the case when the code point is invalid for one value 
but valid for the other? I feel using `'?'` as the missing character can cause 
unexpected behavior in such case.



##########
pinot-segment-local/src/main/java/org/apache/pinot/segment/local/io/util/ValueReaderComparisons.java:
##########
@@ -0,0 +1,174 @@
+/**
+ * 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.pinot.segment.local.io.util;
+
+import java.nio.ByteBuffer;
+import java.nio.ByteOrder;
+import org.apache.pinot.segment.spi.memory.PinotDataBuffer;
+
+public class ValueReaderComparisons {
+
+    private ValueReaderComparisons() {
+    }
+
+    private static int mismatch(PinotDataBuffer dataBuffer, long startOffset, 
int length, ByteBuffer buffer) {
+        boolean littleEndian = dataBuffer.order() == ByteOrder.LITTLE_ENDIAN;
+        if (littleEndian) {
+            buffer.order(ByteOrder.LITTLE_ENDIAN);
+        }
+        int limit = Math.min(length, buffer.limit());
+        int loopBound = limit & ~0x3F;
+        int i = 0;
+        for (; i < loopBound; i += 8) {
+            long ours = dataBuffer.getLong(startOffset + i);
+            long theirs = buffer.getLong(i);
+            if (ours != theirs) {
+                long difference = ours ^ theirs;
+                return i + ((littleEndian
+                        ? Long.numberOfTrailingZeros(difference)
+                        : Long.numberOfLeadingZeros(difference)) >>> 3);
+            }
+        }
+        for (; i < limit; i++) {
+            byte ours = dataBuffer.getByte(startOffset + i);
+            byte theirs = buffer.get(i);
+            if (ours != theirs) {
+                return i;
+            }
+        }
+        return -1;
+    }
+
+    static int compareUtf8Bytes(PinotDataBuffer dataBuffer, long startOffset, 
int length, boolean padded,
+                           byte[] bytes) {
+        // can use MethodHandles.byteArrayViewVarHandle here after dropping 
JDK8
+        ByteBuffer buffer = ByteBuffer.wrap(bytes);
+        int mismatchPosition = mismatch(dataBuffer, startOffset, length, 
buffer);
+        if (mismatchPosition == -1) {
+            // need to figure out whether the unpadded string is longer than 
the parameter or not
+            if (padded && bytes.length < length) {
+                if (bytes.length == 0) {

Review Comment:
   Since we don't allow zero byte in unpadded string, IMO we don't need to 
handle comparison with trailing zero byte in parameter, and we can simplify it 
by always `return dataBuffer.getByte(startOffset + bytes.length) == 0 ? 0 : 
1;`. Essentially we count them as equal when the comparison value has trailing 
zero.



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