[GitHub] [iceberg] aokolnychyi commented on a diff in pull request #5301: Core: Support building custom tasks in ManifestGroup

[GitBox <gi...@apache.org>]

aokolnychyi commented on code in PR #5301:
URL: https://github.com/apache/iceberg/pull/5301#discussion_r923837639


##########
core/src/main/java/org/apache/iceberg/ManifestGroup.java:
##########
@@ -279,4 +287,84 @@ public void close() throws IOException {
           }
         });
   }
+
+  abstract static class ScanTaskFactory<T extends ScanTask> {
+    private final String schemaAsString;
+    private final String specAsString;
+    private final DeleteFileIndex deletes;
+    private final ResidualEvaluator residuals;
+    private final boolean dropStats;
+
+    ScanTaskFactory(PartitionSpec spec, DeleteFileIndex deletes, ResidualEvaluator residuals, boolean dropStats) {
+      this.schemaAsString = SchemaParser.toJson(spec.schema());
+      this.specAsString = PartitionSpecParser.toJson(spec);
+      this.deletes = deletes;
+      this.residuals = residuals;
+      this.dropStats = dropStats;
+    }
+
+    abstract CloseableIterable<T> createTasks(CloseableIterable<ManifestEntry<DataFile>> entries);
+
+    String schemaAsString() {
+      return schemaAsString;
+    }
+
+    String specAsString() {
+      return specAsString;
+    }
+
+    DeleteFileIndex deletes() {
+      return deletes;
+    }
+
+    ResidualEvaluator residuals() {
+      return residuals;
+    }
+
+    boolean shouldKeepStats() {
+      return !dropStats;
+    }
+
+    abstract static class Builder<T extends ScanTask> {

Review Comment:
   I am not super happy with having a builder as it adds more complexity. However, I did it this way so that we can have a loading cache of task factories per spec in `ManifestGroup`. Right now, we parse schema and spec JSON representations for each manifest, which is not required. As those JSON objects can get pretty large, I feel doing the parsing once per spec is an important optimization.
   
   If we want to get rid of the builder, then I'll have to implement per spec caching in each task factory.



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