[VL] Support config velox parquet writer option enableStoreDecimalAsInteger for write parquet

backends-velox/src/main/scala/org/apache/spark/sql/execution/datasources/velox/VeloxParquetWriterInjects.scala

@@ -31,6 +31,9 @@ class VeloxParquetWriterInjects extends VeloxFormatWriterInjects {
     // i.e., compression, block size, block rows.
     val sparkOptions = new mutable.HashMap[String, String]()
     sparkOptions.put(SQLConf.PARQUET_COMPRESSION.key, compressionCodec)
+    sparkOptions.put(
+      SQLConf.PARQUET_WRITE_LEGACY_FORMAT.key,
+      SQLConf.get.writeLegacyParquetFormat.toString)
     val blockSize = options.getOrElse(
       GlutenConfig.PARQUET_BLOCK_SIZE,
       GlutenConfig.get.columnarParquetWriteBlockSize.toString)

cpp/core/config/GlutenConfig.h

@@ -71,6 +71,14 @@ const std::string kParquetWriterVersion = "parquet.writer.version";
 
 const std::string kParquetCompressionCodec = "spark.sql.parquet.compression.codec";
 
+/// Spark `spark.sql.parquet.writeLegacyFormat` (passed from the JVM as "true"/"false").
+/// Used in VeloxWriterUtils to set `WriterOptions::enableStoreDecimalAsInteger` (inverted).
+/// Velox decimal storage when enableStoreDecimalAsInteger is:
+/// - true (Spark legacy off / unset): INT32/INT64 for short DECIMAL precisions; higher precisions
+///   use FIXED_LEN_BYTE_ARRAY.
+/// - false (Spark legacy on): FIXED_LEN_BYTE_ARRAY for all DECIMAL precisions.
+const std::string kParquetStoreDecimalAsInteger = "spark.sql.parquet.writeLegacyFormat";
+
 const std::string kColumnarToRowMemoryThreshold = "spark.gluten.sql.columnarToRowMemoryThreshold";
 
 const std::string kUGIUserName = "spark.gluten.ugi.username";

cpp/velox/utils/VeloxWriterUtils.cc

@@ -49,6 +49,17 @@ std::unique_ptr<WriterOptions> makeParquetWriteOption(const std::unordered_map<s
   }
   auto writeOption = std::make_unique<WriterOptions>();
   writeOption->parquetWriteTimestampUnit = TimestampPrecision::kMicroseconds /*micro*/;
+  bool writeLegacyParquetFormat = false;
+  if (auto it = sparkConfs.find(kParquetStoreDecimalAsInteger); it != sparkConfs.end()) {
+    writeLegacyParquetFormat = boost::iequals(it->second, "true");
+  }
+  // Maps spark.sql.parquet.writeLegacyFormat to Velox enableStoreDecimalAsInteger (inverted).
+  // Controls how DECIMAL values are stored by the Writer:
+  // - true (default when legacy format is off): store as integer using INT32/INT64 for short
+  //   DECIMAL precisions; higher precisions use FIXED_LEN_BYTE_ARRAY.
+  // - false (when spark.sql.parquet.writeLegacyFormat is true): store as FIXED_LEN_BYTE_ARRAY
+  //   regardless of precision (Spark legacy Parquet decimal layout).
+  writeOption->enableStoreDecimalAsInteger = !writeLegacyParquetFormat;
   auto compressionCodec = CompressionKind::CompressionKind_SNAPPY;
   if (auto it = sparkConfs.find(kParquetCompressionCodec); it != sparkConfs.end()) {
     auto compressionCodecStr = it->second;

gluten-substrait/src/main/scala/org/apache/gluten/config/GlutenConfig.scala

@@ -633,6 +633,7 @@ object GlutenConfig extends ConfigRegistry {
       DEBUG_ENABLED.key,
       // datasource config
       SPARK_SQL_PARQUET_COMPRESSION_CODEC,
+      SQLConf.PARQUET_WRITE_LEGACY_FORMAT.key,
       // datasource config end
       GlutenCoreConfig.COLUMNAR_OVERHEAD_SIZE_IN_BYTES.key,
       GlutenCoreConfig.COLUMNAR_OFFHEAP_SIZE_IN_BYTES.key,