fix the append read

core/workflow-core/src/main/scala/edu/uci/ics/amber/core/storage/result/iceberg/IcebergDocument.scala

@@ -49,32 +49,44 @@ class IcebergDocument[T >: Null <: AnyRef](
   override def get(): Iterator[T] = {
     new Iterator[T] {
       private var table: Option[Table] = loadTable()
-      private var currentSnapshot: Option[Snapshot] =
-        table.flatMap(t => Option(t.currentSnapshot()))
+      private var lastSnapshotId: Option[Long] = None
       private var recordIterator: Iterator[T] = loadRecords()
 
       /**
-        * Loads the table, handling cases where it may not exist.
-        */
+       * Loads the table, handling cases where it may not exist.
+       */
       private def loadTable(): Option[Table] = {
-        IcebergUtil.loadTable(
-          catalog,
-          tableNamespace,
-          tableName,
-          tableSchema,
-          createIfNotExist = false
-        )
+        IcebergUtil.loadTable(catalog, tableNamespace, tableName, tableSchema, createIfNotExist = false)
       }
 
       /**
-        * Loads all records from the current snapshot.
-        */
+       * Loads records incrementally using `newIncrementalAppendScan` from the last snapshot ID.
+       */
       private def loadRecords(): Iterator[T] = {
         table match {
-          case Some(t) if currentSnapshot.isDefined =>
+          case Some(t) =>
             try {
-              val records: CloseableIterable[Record] = IcebergGenerics.read(t).build()
+              val currentSnapshot = Option(t.currentSnapshot())
+              val currentSnapshotId = currentSnapshot.map(_.snapshotId())
+
+              val records: CloseableIterable[Record] = (lastSnapshotId, currentSnapshotId) match {
+                case (Some(lastId), Some(currId)) if lastId != currId =>
+                  // Perform incremental append scan if snapshot IDs are different
+                  IcebergGenerics.read(t).appendsAfter(lastId).build()
+
+                case (None, Some(_)) =>
+                  // First read, perform a full scan
+                  IcebergGenerics.read(t).build()
+
+                case _ =>
+                  // No new data; return an empty iterator
+                  CloseableIterable.empty()
+              }
+
+              // Update the last snapshot ID to the current one
+              lastSnapshotId = currentSnapshotId
               records.iterator().asScala.map(record => deserde(tableSchema, record))
+
             } catch {
               case _: java.io.FileNotFoundException =>
                 println("Metadata file not found. Returning an empty iterator.")
@@ -84,6 +96,7 @@ class IcebergDocument[T >: Null <: AnyRef](
                 e.printStackTrace()
                 Iterator.empty
             }
+
           case _ => Iterator.empty
         }
       }
@@ -95,15 +108,8 @@ class IcebergDocument[T >: Null <: AnyRef](
           // Refresh the table and check for new commits
           table = loadTable()
           table.foreach(_.refresh())
-          val newSnapshot = table.flatMap(t => Option(t.currentSnapshot()))
-
-          if (newSnapshot != currentSnapshot) {
-            currentSnapshot = newSnapshot
-            recordIterator = loadRecords()
-            recordIterator.hasNext
-          } else {
-            false
-          }
+          recordIterator = loadRecords()
+          recordIterator.hasNext
         }
       }