From 1ab923c16b46fade36fb52497e34f7615340fa02 Mon Sep 17 00:00:00 2001
From: Norbert Orzechowicz <contact@norbert.tech>
Date: Thu, 5 Mar 2026 09:47:28 -0600
Subject: [PATCH] fix: parquet statistics

dont save string length into min/max statistics
---
 .../ParquetFile/RowGroup/StatisticsReader.php |  8 ++--
 .../Flow/Parquet/Writer/StatisticsCounter.php | 22 +++++++--
 .../Unit/Writer/StatisticsCounterTest.php     | 47 +++++++++++++++++++
 3 files changed, 70 insertions(+), 7 deletions(-)

diff --git a/src/lib/parquet/src/Flow/Parquet/ParquetFile/RowGroup/StatisticsReader.php b/src/lib/parquet/src/Flow/Parquet/ParquetFile/RowGroup/StatisticsReader.php
index 59ccc932f5..65a408d70b 100644
--- a/src/lib/parquet/src/Flow/Parquet/ParquetFile/RowGroup/StatisticsReader.php
+++ b/src/lib/parquet/src/Flow/Parquet/ParquetFile/RowGroup/StatisticsReader.php
@@ -27,7 +27,7 @@ public function max(FlatColumn $column) : mixed
             return null;
         }
 
-        if (ColumnPrimitiveType::isString($column) && \mb_check_encoding($this->statistics->max, 'UTF-8')) {
+        if (ColumnPrimitiveType::isString($column)) {
             return $this->statistics->max;
         }
 
@@ -40,7 +40,7 @@ public function maxValue(FlatColumn $column) : mixed
             return null;
         }
 
-        if (ColumnPrimitiveType::isString($column) && \mb_check_encoding($this->statistics->maxValue, 'UTF-8')) {
+        if (ColumnPrimitiveType::isString($column)) {
             return $this->statistics->maxValue;
         }
 
@@ -53,7 +53,7 @@ public function min(FlatColumn $column) : mixed
             return null;
         }
 
-        if (ColumnPrimitiveType::isString($column) && \mb_check_encoding($this->statistics->min, 'UTF-8')) {
+        if (ColumnPrimitiveType::isString($column)) {
             return $this->statistics->min;
         }
 
@@ -66,7 +66,7 @@ public function minValue(FlatColumn $column) : mixed
             return null;
         }
 
-        if (ColumnPrimitiveType::isString($column) && \mb_check_encoding($this->statistics->minValue, 'UTF-8')) {
+        if (ColumnPrimitiveType::isString($column)) {
             return $this->statistics->minValue;
         }
 
diff --git a/src/lib/parquet/src/Flow/Parquet/Writer/StatisticsCounter.php b/src/lib/parquet/src/Flow/Parquet/Writer/StatisticsCounter.php
index 58ded18d02..4867d13e4b 100644
--- a/src/lib/parquet/src/Flow/Parquet/Writer/StatisticsCounter.php
+++ b/src/lib/parquet/src/Flow/Parquet/Writer/StatisticsCounter.php
@@ -9,7 +9,7 @@
 use Flow\Parquet\Data\PlainValuesPacker;
 use Flow\Parquet\Dremel\Statistics\Comparator;
 use Flow\Parquet\Exception\InvalidArgumentException;
-use Flow\Parquet\ParquetFile\Schema\FlatColumn;
+use Flow\Parquet\ParquetFile\Schema\{FlatColumn, PhysicalType};
 use Flow\Parquet\ParquetFile\Statistics;
 
 final class StatisticsCounter
@@ -126,8 +126,24 @@ public function toStatistics() : Statistics
         $minBuffer = '';
         $maxBuffer = '';
 
-        (new PlainValuesPacker(new BinaryBufferWriter($minBuffer)))->packValues($this->column, [$this->min()]);
-        (new PlainValuesPacker(new BinaryBufferWriter($maxBuffer)))->packValues($this->column, [$this->max()]);
+        $min = $this->min();
+        $max = $this->max();
+
+        if ($min !== null) {
+            if ($this->column->type() === PhysicalType::BYTE_ARRAY && \is_string($min)) {
+                (new BinaryBufferWriter($minBuffer))->append($min);
+            } else {
+                (new PlainValuesPacker(new BinaryBufferWriter($minBuffer)))->packValues($this->column, [$min]);
+            }
+        }
+
+        if ($max !== null) {
+            if ($this->column->type() === PhysicalType::BYTE_ARRAY && \is_string($max)) {
+                (new BinaryBufferWriter($maxBuffer))->append($max);
+            } else {
+                (new PlainValuesPacker(new BinaryBufferWriter($maxBuffer)))->packValues($this->column, [$max]);
+            }
+        }
 
         return new Statistics(
             max: $maxBuffer !== '' ? $maxBuffer : null,
diff --git a/src/lib/parquet/tests/Flow/Parquet/Tests/Unit/Writer/StatisticsCounterTest.php b/src/lib/parquet/tests/Flow/Parquet/Tests/Unit/Writer/StatisticsCounterTest.php
index 988e85f926..5873cdf639 100644
--- a/src/lib/parquet/tests/Flow/Parquet/Tests/Unit/Writer/StatisticsCounterTest.php
+++ b/src/lib/parquet/tests/Flow/Parquet/Tests/Unit/Writer/StatisticsCounterTest.php
@@ -463,6 +463,53 @@ public function test_reset() : void
         self::assertNull($statistics->max());
     }
 
+    public function test_to_statistics_encodes_byte_array_without_length_prefix() : void
+    {
+        $column = FlatColumn::string('test_column');
+        $statistics = new StatisticsCounter($column);
+
+        $statistics->add('hello');
+        $statistics->add('world');
+
+        $result = $statistics->toStatistics();
+
+        self::assertSame('hello', $result->min);
+        self::assertSame('world', $result->max);
+        self::assertSame('hello', $result->minValue);
+        self::assertSame('world', $result->maxValue);
+    }
+
+    public function test_to_statistics_with_int32_encodes_with_packer() : void
+    {
+        $column = FlatColumn::int32('test_column');
+        $statistics = new StatisticsCounter($column);
+
+        $statistics->add(5);
+        $statistics->add(10);
+
+        $result = $statistics->toStatistics();
+
+        self::assertSame(\pack('l', 5), $result->min);
+        self::assertSame(\pack('l', 10), $result->max);
+    }
+
+    public function test_to_statistics_with_null_values_does_not_encode() : void
+    {
+        $column = FlatColumn::string('test_column');
+        $statistics = new StatisticsCounter($column);
+
+        $statistics->add(null);
+        $statistics->add(null);
+
+        $result = $statistics->toStatistics();
+
+        self::assertNull($result->min);
+        self::assertNull($result->max);
+        self::assertNull($result->minValue);
+        self::assertNull($result->maxValue);
+        self::assertSame(2, $result->nullCount);
+    }
+
     public function test_values_count_calculation_with_arrays() : void
     {
         $column = FlatColumn::string('test_column');