feat(bigquery-jdbc): optimize memory footprint for JSON result set streaming (#13660)

b/529436374

- Centralizes row-unpacking logic into `BigQueryFieldValueListWrapper`
using a static, stateless utility pattern to reduce object allocations
during JSON result set parsing.
- Pre-computes complex column flags (`ARRAY`, `STRUCT`, `RANGE`) outside
the page-fetching loop in `BigQueryStatement` to avoid redundant per-row
inspection.
- Preserves raw `FieldValue` references for complex types (`RANGE`,
`ARRAY`, `STRUCT`) during row unpacking to prevent improper string
coercion.

Author: Neenu1995

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryDatabaseMetaData.java

@@ -4923,12 +4923,14 @@ private void populateQueue(
       FieldList resultSchemaFields) {
     LOG.info("Populating queue with %d results...", collectedResults.size());
     try {
+      boolean[] isComplexColumn =
+          BigQueryFieldValueListWrapper.createComplexColumnFlags(resultSchemaFields);
       for (FieldValueList sortedRow : collectedResults) {
         if (Thread.currentThread().isInterrupted()) {
           LOG.warning("Interrupted during queue population.");
           break;
         }
-        queue.put(BigQueryFieldValueListWrapper.of(resultSchemaFields, sortedRow));
+        queue.put(BigQueryFieldValueListWrapper.of(resultSchemaFields, sortedRow, isComplexColumn));
       }
       LOG.info("Finished populating queue.");
     } catch (InterruptedException e) {
@@ -4967,7 +4969,7 @@ private void signalEndOfData(
     try {
       LOG.info("Adding end signal to queue.");
       BigQueryFieldValueListWrapper element =
-          BigQueryFieldValueListWrapper.of(resultSchemaFields, null, true);
+          BigQueryFieldValueListWrapper.ofEndOfStream(resultSchemaFields);
       if (!queue.offer(element)) {
         boolean wasInterrupted = Thread.interrupted();
         try {

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryFieldValueListWrapper.java

@@ -16,14 +16,20 @@
 
 package com.google.cloud.bigquery.jdbc;
 
+import static com.google.cloud.bigquery.jdbc.BigQueryBaseArray.isArray;
+import static com.google.cloud.bigquery.jdbc.BigQueryBaseStruct.isStruct;
+
+import com.google.cloud.bigquery.Field;
 import com.google.cloud.bigquery.FieldList;
 import com.google.cloud.bigquery.FieldValue;
+import com.google.cloud.bigquery.FieldValue.Attribute;
 import com.google.cloud.bigquery.FieldValueList;
+import com.google.cloud.bigquery.StandardSQLTypeName;
 import java.util.List;
 
 /**
  * Package-private, This class acts as a facade layer and wraps the FieldList(schema) and
- * FieldValueList
+ * FieldValueList or lightweight Object[] row buffers.
  */
 class BigQueryFieldValueListWrapper {
 
@@ -37,57 +43,129 @@ class BigQueryFieldValueListWrapper {
   // reference as a List<FieldValue> in case of an Array
   private final List<FieldValue> arrayFieldValueList;
 
+  // Lightweight row values buffer (Object[]) for streaming parsing
+  private final Object[] rowValues;
+
   // This flag marks the end of the stream for the ResultSet
   private boolean isLast = false;
   private final Exception exception;
 
+  static BigQueryFieldValueListWrapper ofEndOfStream(FieldList fieldList) {
+    return new BigQueryFieldValueListWrapper(fieldList, null, null, null, true, null);
+  }
+
   static BigQueryFieldValueListWrapper of(
-      FieldList fieldList, FieldValueList fieldValueList, boolean... isLast) {
-    boolean isLastFlag = isLast != null && isLast.length == 1 && isLast[0];
-    return new BigQueryFieldValueListWrapper(fieldList, fieldValueList, null, isLastFlag, null);
+      FieldList fieldList, FieldValueList fieldValueList, boolean[] isComplexColumn) {
+    boolean[] flags =
+        isComplexColumn != null ? isComplexColumn : createComplexColumnFlags(fieldList);
+    Object[] rowValues = unpackRow(fieldValueList, flags);
+    return new BigQueryFieldValueListWrapper(fieldList, null, null, rowValues, false, null);
+  }
+
+  static boolean[] createComplexColumnFlags(FieldList fieldList) {
+    if (fieldList == null) {
+      return new boolean[0];
+    }
+    int size = fieldList.size();
+    boolean[] isComplex = new boolean[size];
+    for (int i = 0; i < size; i++) {
+      Field field = fieldList.get(i);
+      isComplex[i] =
+          isArray(field)
+              || isStruct(field)
+              || (field.getType() != null
+                  && field.getType().getStandardType() == StandardSQLTypeName.RANGE);
+    }
+    return isComplex;
+  }
+
+  static Object[] unpackRow(FieldValueList fieldValueList, boolean[] isComplexColumn) {
+    if (fieldValueList == null) {
+      return null;
+    }
+    int size = fieldValueList.size();
+    Object[] row = new Object[size];
+    for (int i = 0; i < size; i++) {
+      FieldValue fv = fieldValueList.get(i);
+      if (fv == null || fv.isNull()) {
+        row[i] = null;
+      } else if ((i < isComplexColumn.length && isComplexColumn[i])
+          || fv.getAttribute() != Attribute.PRIMITIVE) {
+        row[i] = fv;
+      } else {
+        row[i] = fv.getStringValue();
+      }
+    }
+    return row;
   }
 
   static BigQueryFieldValueListWrapper getNestedFieldValueListWrapper(
       FieldList fieldList, List<FieldValue> arrayFieldValueList, boolean... isLast) {
     boolean isLastFlag = isLast != null && isLast.length == 1 && isLast[0];
     return new BigQueryFieldValueListWrapper(
-        fieldList, null, arrayFieldValueList, isLastFlag, null);
+        fieldList, null, arrayFieldValueList, null, isLastFlag, null);
   }
 
   static BigQueryFieldValueListWrapper ofError(Exception exception) {
-    return new BigQueryFieldValueListWrapper(null, null, null, true, exception);
+    return new BigQueryFieldValueListWrapper(null, null, null, null, true, exception);
   }
 
   private BigQueryFieldValueListWrapper(
       FieldList fieldList,
       FieldValueList fieldValueList,
       List<FieldValue> arrayFieldValueList,
+      Object[] rowValues,
       boolean isLast,
       Exception exception) {
     this.fieldList = fieldList;
     this.fieldValueList = fieldValueList;
     this.arrayFieldValueList = arrayFieldValueList;
+    this.rowValues = rowValues;
     this.isLast = isLast;
     this.exception = exception;
   }
 
-  public FieldList getFieldList() {
+  FieldList getFieldList() {
     return this.fieldList;
   }
 
-  public FieldValueList getFieldValueList() {
+  FieldValueList getFieldValueList() {
     return this.fieldValueList;
   }
 
-  public List<FieldValue> getArrayFieldValueList() {
+  List<FieldValue> getArrayFieldValueList() {
     return this.arrayFieldValueList;
   }
 
-  public boolean isLast() {
+  Object[] getRowValues() {
+    return this.rowValues;
+  }
+
+  FieldValue get(int index) {
+    if (this.fieldValueList != null) {
+      return this.fieldValueList.get(index);
+    }
+    if (this.arrayFieldValueList != null) {
+      return this.arrayFieldValueList.get(index);
+    }
+    if (this.rowValues != null && index >= 0 && index < this.rowValues.length) {
+      Object val = this.rowValues[index];
+      if (val == null) {
+        return FieldValue.of(Attribute.PRIMITIVE, null);
+      }
+      if (val instanceof FieldValue) {
+        return (FieldValue) val;
+      }
+      return FieldValue.of(Attribute.PRIMITIVE, val.toString());
+    }
+    return null;
+  }
+
+  boolean isLast() {
     return this.isLast;
   }
 
-  public Exception getException() {
+  Exception getException() {
     return this.exception;
   }
 }

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryJsonResultSet.java

@@ -299,7 +299,7 @@ private FieldValue getObjectInternal(int columnIndex) throws SQLException {
     // non nested, return the value
     else {
       // SQL Index to 0 based index
-      value = this.cursor.getFieldValueList().get(columnIndex - 1);
+      value = this.cursor.get(columnIndex - 1);
     }
     setWasNull(value.getValue());
     return value;

java-bigquery-jdbc/src/main/java/com/google/cloud/bigquery/jdbc/BigQueryStatement.java

@@ -1252,6 +1252,9 @@ Future<?> parseAndPopulateRpcDataAsync(
         () -> { // producer thread populating the buffer
           try {
             Iterable<FieldValueList> fieldValueLists;
+            boolean[] isComplexColumn =
+                BigQueryFieldValueListWrapper.createComplexColumnFlags(
+                    schema != null ? schema.getFields() : null);
             // as we have to process the first page
             boolean hasRows = true;
             while (hasRows) {
@@ -1288,7 +1291,8 @@ Future<?> parseAndPopulateRpcDataAsync(
                 }
                 Uninterruptibles.putUninterruptibly(
                     bigQueryFieldValueListWrapperBlockingQueue,
-                    BigQueryFieldValueListWrapper.of(schema.getFields(), fieldValueList));
+                    BigQueryFieldValueListWrapper.of(
+                        schema.getFields(), fieldValueList, isComplexColumn));
                 results += 1;
               }
               LOG.fine(
@@ -1746,6 +1750,6 @@ private void enqueueBufferError(BlockingQueue<BigQueryFieldValueListWrapper> que
   }
 
   private void enqueueBufferEndOfStream(BlockingQueue<BigQueryFieldValueListWrapper> queue) {
-    Uninterruptibles.putUninterruptibly(queue, BigQueryFieldValueListWrapper.of(null, null, true));
+    Uninterruptibles.putUninterruptibly(queue, BigQueryFieldValueListWrapper.ofEndOfStream(null));
   }
 }