[GitHub] [iceberg] szehon-ho commented on a diff in pull request #5376: Core: Add readable metrics columns to files metadata tables

[GitBox]

szehon-ho commented on code in PR #5376:
URL: https://github.com/apache/iceberg/pull/5376#discussion_r1022594631


##########
core/src/main/java/org/apache/iceberg/BaseFilesTable.java:
##########
@@ -140,42 +142,75 @@ protected CloseableIterable<FileScanTask> doPlanFiles() {
   }
 
   static class ManifestReadTask extends BaseFileScanTask implements DataTask {
+
+    private static final Set<Integer> READABLE_METRICS_FIELD_IDS =
+        TypeUtil.getProjectedIds(DataFile.READABLE_METRICS.type());
+    private static final Schema MIN_PROJECTION_FOR_READABLE_METRICS =
+        new Schema(
+            DataFile.COLUMN_SIZES,
+            DataFile.VALUE_COUNTS,
+            DataFile.NULL_VALUE_COUNTS,
+            DataFile.NAN_VALUE_COUNTS,
+            DataFile.LOWER_BOUNDS,
+            DataFile.UPPER_BOUNDS);
+
     private final FileIO io;
     private final Map<Integer, PartitionSpec> specsById;
     private final ManifestFile manifest;
-    private final Schema schema;
+    private final Schema dataTableSchema;
+    private final Schema projection;
 
     ManifestReadTask(
         Table table,
         ManifestFile manifest,
-        Schema schema,
+        Schema projection,
         String schemaString,
         String specString,
         ResidualEvaluator residuals) {
       super(DataFiles.fromManifest(manifest), null, schemaString, specString, 
residuals);
       this.io = table.io();
       this.specsById = Maps.newHashMap(table.specs());
       this.manifest = manifest;
-      this.schema = schema;
+      this.dataTableSchema = table.schema();
+      this.projection = projection;
     }
 
     @Override
     public CloseableIterable<StructLike> rows() {
-      return CloseableIterable.transform(manifestEntries(), file -> 
(StructLike) file);
+      if (projection.findColumnName(DataFile.READABLE_METRICS.fieldId()) == 
null) {
+        return CloseableIterable.transform(files(projection), file -> 
(StructLike) file);
+      } else {
+        Schema fileProjection = TypeUtil.selectNot(projection, 
READABLE_METRICS_FIELD_IDS);
+
+        // If readable_metrics is selected,
+        // original metrics columns need to be selected for derivation
+        Schema minProjection = TypeUtil.join(fileProjection, 
MIN_PROJECTION_FOR_READABLE_METRICS);

Review Comment:
   Hm not sure what is a good name.  To me max projection is not right (that 
would just be all the columns of files table).  So I just put projection for 
now, and we can optimize it later?



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