[GitHub] [drill] arina-ielchiieva commented on a change in pull request #2051: DRILL-7696: EVF v2 scan schema resolution

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arina-ielchiieva commented on a change in pull request #2051: DRILL-7696: EVF v2 scan schema resolution
URL: https://github.com/apache/drill/pull/2051#discussion_r407073746
 
 

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 File path: exec/java-exec/src/main/java/org/apache/drill/exec/physical/impl/scan/v3/schema/ScanSchemaResolver.java
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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.drill.exec.physical.impl.scan.v3.schema;
+
+import org.apache.drill.common.exceptions.CustomErrorContext;
+import org.apache.drill.common.exceptions.UserException;
+import org.apache.drill.exec.physical.impl.scan.v3.schema.DynamicSchemaFilter.DynamicTupleFilter;
+import org.apache.drill.exec.physical.impl.scan.v3.schema.MutableTupleMetadata.ColumnHandle;
+import org.apache.drill.exec.physical.impl.scan.v3.schema.ScanSchemaTracker.ProjectionType;
+import org.apache.drill.exec.physical.resultSet.impl.ProjectionFilter;
+import org.apache.drill.exec.physical.resultSet.impl.ProjectionFilter.ProjResult;
+import org.apache.drill.exec.record.metadata.ColumnMetadata;
+import org.apache.drill.exec.record.metadata.DynamicColumn;
+import org.apache.drill.exec.record.metadata.TupleMetadata;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Resolves a schema against the existing scan schema.
+ * Expands columns by comparing the existing scan schema with
+ * a "revised" (provided or reader) schema, adjusting the scan schema
+ * accordingly. Maps are expanded recursively. Other columns
+ * must match types (concrete columns) or the type must match projection
+ * (for dynamic columns.)
+ * <ul>
+ * <li>Resolves a provided schema against the projection list.
+ * The provided schema can be strict (converts a wildcard into
+ * an explicit projection) or lenient (the reader can add
+ * additional columns to a wildcard.)</li>
+ * <li>Resolves an early reader schema against the projection list
+ * and optional provided schema.</li>
+ * <li>Resolves a reader output schema against a dynamic (projection
+ * list), concreted (provided or prior reader) schema) or combination.
+ * </ul>
+ * <p>
+ * In practice, the logic is simpler: given a schema (dynamic, concrete
+ * or combination), further resolve the schema using the input schema
+ * provided. Resolve dynamic columns, verify consistency of concrete
+ * columns.
+ * <p>
+ * Projected columns start as <i>dynamic</i> (no type). Columns
+ * are resolved to a known type as a schema identifies that type.
+ * Subsequent schemas are obligated to use that same type to avoid
+ * an inconsistent schema change downstream.
+ * <p>
+ * Expands columns by comparing the existing scan schema with
+ * a "revised" (provided or reader) schema, adjusting the scan schema
+ * accordingly. Maps are expanded recursively. Other columns
+ * must match types (concrete columns) or the type must match projection
+ * (for dynamic columns.)
+ * <p>
+ * A "resolved" projection list is a list of concrete columns: table
+ * columns, nulls, file metadata or partition metadata. An unresolved list
+ * has either table column names, but no match, or a wildcard column.
+ * <p>
+ * The idea is that the projection list moves through stages of resolution
+ * depending on which information is available. An "early schema" table
+ * provides schema information up front, and so allows fully resolving
+ * the projection list on table open. A "late schema" table allows only a
+ * partially resolved projection list, with the remainder of resolution
+ * happening on the first (or perhaps every) batch.
+ */
+public class ScanSchemaResolver {
+  private static final Logger logger = LoggerFactory.getLogger(ScanSchemaResolver.class);
+
+  public enum Mode {
+    STRICT_PROVIDED_SCHEMA,
+    LENIENT_PROVIDED_SCHEMA,
+    EARLY_READER_SCHEMA,
+    READER_SCHEMA,
+    MISSING_COLS
+  }
+
+  private final MutableTupleMetadata schema;
+  private final Mode mode;
+  private final boolean isProjectAll;
+  private final boolean allowMapAdditions;
+  private final String source;
+  private final CustomErrorContext errorContext;
+
+  public ScanSchemaResolver(MutableTupleMetadata schema, Mode mode,
+      boolean allowMapAdditions,
+      CustomErrorContext errorContext) {
+    this.schema = schema;
+    this.isProjectAll = schema.projectionType() == ProjectionType.ALL;
+    this.mode = mode;
+    this.errorContext = errorContext;
+    this.allowMapAdditions = allowMapAdditions;
+    switch (mode) {
+      case LENIENT_PROVIDED_SCHEMA:
 
 Review comment:
   You enum can have this names already and you won't have to do the switch:
   ```
    public enum Mode {
        STRICT_PROVIDED_SCHEMA("Provided),
         ...
   
        private final String source;
   
        Mode(String source) {
          this.source = source;
        }
   
        public String source() {
           return source;
       }
   
      }
   
   ```

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