PLUGIN-1925: Add detailed comments to the code

Author: sgarg-CS

database-commons/src/main/java/io/cdap/plugin/db/source/DataDrivenETLDBInputFormat.java

@@ -132,8 +132,9 @@ public Connection createConnection() {
 
   @Override
   protected DBSplitter getSplitter(int sqlDataType) {
+    // Use SafeBigDecimalSplitter for columns having high precision decimal or numeric columns
     if (sqlDataType == Types.NUMERIC || sqlDataType == Types.DECIMAL) {
-      return new CustomBigDecimalSplitter();
+      return new SafeBigDecimalSplitter();
     }
     return super.getSplitter(sqlDataType);
   }

…/db/source/CustomBigDecimalSplitter.java …in/db/source/SafeBigDecimalSplitter.javadatabase-commons/src/main/java/io/cdap/plugin/db/source/CustomBigDecimalSplitter.java renamed to database-commons/src/main/java/io/cdap/plugin/db/source/SafeBigDecimalSplitter.java database-commons/src/main/java/io/cdap/plugin/db/source/CustomBigDecimalSplitter.java renamed to database-commons/src/main/java/io/cdap/plugin/db/source/SafeBigDecimalSplitter.java

@@ -21,11 +21,22 @@
 import java.math.RoundingMode;
 
 /**
- * Custom implementation of {@link BigDecimalSplitter} to ensures safe and precise division of BigDecimal values while
- * calculating split points for NUMERIC and DECIMAL types.
+ * Safe implementation of {@link BigDecimalSplitter} to ensure precise division of BigDecimal values while calculating
+ * split points for NUMERIC and DECIMAL types.
+ *
+ * <p>Problem: The default {@link BigDecimalSplitter} implementation may return 0 when the numerator is smaller than the
+ * denominator (e.g., 1 / 4 = 0), due to the lack of a defined scale for division. Since the result (0) is smaller than
+ * {@link BigDecimalSplitter#MIN_INCREMENT} (i.e. {@code 10000 * Double.MIN_VALUE}), the split size defaults to
+ * {@code MIN_INCREMENT}, leading to an excessive number of splits (~10M) and potential OOM errors.</p>
+ *
+ * <p>Fix: This implementation derives scale from column metadata, adds a buffer of 5 decimal places, and uses
+ * {@link RoundingMode#HALF_UP} as the rounding mode.</p
+ *
+ * <p>Note: This class is used by {@link DataDrivenETLDBInputFormat}.</p>
  */
-public class CustomBigDecimalSplitter extends BigDecimalSplitter {
+public class SafeBigDecimalSplitter extends BigDecimalSplitter {
 
+  /* An additional buffer of +5 digits is applied to preserve accuracy during division. */
   public static final int SCALE_BUFFER = 5;
   /**
    * Performs safe division with correct scale handling.
@@ -37,7 +48,7 @@ public class CustomBigDecimalSplitter extends BigDecimalSplitter {
    */
   @Override
   protected BigDecimal tryDivide(BigDecimal numerator, BigDecimal denominator) {
-    // Derive scale from numerator/denominator + buffer
+    // Determine the required scale for the division and add a buffer to ensure accuracy
     int effectiveScale = Math.max(numerator.scale(), denominator.scale()) + SCALE_BUFFER;
     return numerator.divide(denominator, effectiveScale, RoundingMode.HALF_UP);
   }

…source/CustomBigDecimalSplitterTest.java …b/source/SafeBigDecimalSplitterTest.javadatabase-commons/src/test/java/io/cdap/plugin/db/source/CustomBigDecimalSplitterTest.java renamed to database-commons/src/test/java/io/cdap/plugin/db/source/SafeBigDecimalSplitterTest.java database-commons/src/test/java/io/cdap/plugin/db/source/CustomBigDecimalSplitterTest.java renamed to database-commons/src/test/java/io/cdap/plugin/db/source/SafeBigDecimalSplitterTest.java

@@ -33,10 +33,10 @@
 import static org.mockito.Mockito.when;
 
 /**
- * Test class for {@link CustomBigDecimalSplitter}
+ * Test class for {@link SafeBigDecimalSplitter}
  */
-public class CustomBigDecimalSplitterTest {
-  private final CustomBigDecimalSplitter splitter = new CustomBigDecimalSplitter();
+public class SafeBigDecimalSplitterTest {
+  private final SafeBigDecimalSplitter splitter = new SafeBigDecimalSplitter();
 
   @Test
   public void testSmallRangeDivision() {
@@ -75,7 +75,7 @@ public void testSplits() throws SQLException {
     when(conf.getInt("mapreduce.job.maps", 1)).thenReturn(numSplits);
     when(resultSet.getBigDecimal(1)).thenReturn(minVal);
     when(resultSet.getBigDecimal(2)).thenReturn(maxVal);
-    BigDecimalSplitter bigDecimalSplitter = new CustomBigDecimalSplitter();
+    BigDecimalSplitter bigDecimalSplitter = new SafeBigDecimalSplitter();
     List<InputSplit> actualSplits = bigDecimalSplitter.split(conf, resultSet, "id");
     assertEquals(numSplits, actualSplits.size());
   }
@@ -91,7 +91,7 @@ public void testSplitsWithMinValueEqualToMaxValue() throws SQLException {
     when(conf.getInt("mapreduce.job.maps", 1)).thenReturn(numSplits);
     when(resultSet.getBigDecimal(1)).thenReturn(minVal);
     when(resultSet.getBigDecimal(2)).thenReturn(maxVal);
-    BigDecimalSplitter bigDecimalSplitter = new CustomBigDecimalSplitter();
+    BigDecimalSplitter bigDecimalSplitter = new SafeBigDecimalSplitter();
     List<InputSplit> actualSplits = bigDecimalSplitter.split(conf, resultSet, "id");
     assertEquals(numSplits, actualSplits.size());
   }