api/src/main/java/org/apache/iceberg/Scan.java

/*
 * 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.iceberg;

import java.util.Collection;
import java.util.concurrent.ExecutorService;
import org.apache.iceberg.expressions.Expression;
import org.apache.iceberg.io.CloseableIterable;

/**
 * Scan objects are immutable and can be shared between threads. Refinement methods, like
 * {@link #select(Collection)} and {@link #filter(Expression)}, create new TableScan instances.
 *
 * @param <ThisT> the child Java API class, returned by method chaining
 * @param <T> the Java type of tasks produces by this scan
 * @param <G> the Java type of task groups produces by this scan
 */
public interface Scan<ThisT, T extends ScanTask, G extends ScanTaskGroup<T>> {
  /**
   * Create a new scan from this scan's configuration that will override the {@link Table}'s behavior based
   * on the incoming pair. Unknown properties will be ignored.
   *
   * @param property name of the table property to be overridden
   * @param value value to override with
   * @return a new scan based on this with overridden behavior
   */
  ThisT option(String property, String value);

  /**
   * Create a new scan from this with the schema as its projection.
   *
   * @param schema a projection schema
   * @return a new scan based on this with the given projection
   */
  ThisT project(Schema schema);

  /**
   * Create a new scan from this that, if data columns where selected
   * via {@link #select(java.util.Collection)}, controls whether the match to the schema will be done
   * with case sensitivity. Default is true.
   *
   * @return a new scan based on this with case sensitivity as stated
   */
  ThisT caseSensitive(boolean caseSensitive);

  /**
   * Create a new scan from this that loads the column stats with each data file.
   * <p>
   * Column stats include: value count, null value count, lower bounds, and upper bounds.
   *
   * @return a new scan based on this that loads column stats.
   */
  ThisT includeColumnStats();

  /**
   * Create a new scan from this that will read the given data columns. This produces
   * an expected schema that includes all fields that are either selected or used by this scan's
   * filter expression.
   *
   * @param columns column names from the table's schema
   * @return a new scan based on this with the given projection columns
   */
  ThisT select(Collection<String> columns);

  /**
   * Create a new scan from the results of this filtered by the {@link Expression}.
   *
   * @param expr a filter expression
   * @return a new scan based on this with results filtered by the expression
   */
  ThisT filter(Expression expr);

  /**
   * Create a new scan from this that applies data filtering to files but not to rows in those files.
   *
   * @return a new scan based on this that does not filter rows in files.
   */
  ThisT ignoreResiduals();

  /**
   * Create a new scan to use a particular executor to plan. The default worker pool will be
   * used by default.
   *
   * @param executorService the provided executor
   * @return a table scan that uses the provided executor to access manifests
   */
  ThisT planWith(ExecutorService executorService);

  /**
   * Returns this scan's projection {@link Schema}.
   * <p>
   * If the projection schema was set directly using {@link #project(Schema)}, returns that schema.
   * <p>
   * If the projection schema was set by calling {@link #select(Collection)}, returns a projection
   * schema that includes the selected data fields and any fields used in the filter expression.
   *
   * @return this scan's projection schema
   */
  Schema schema();

  /**
   * Plan tasks for this scan where each task reads a single file.
   * <p>
   * Use {@link #planTasks()} for planning balanced tasks where each task will read either a single file,
   * a part of a file, or multiple files.
   *
   * @return an Iterable of tasks scanning entire files required by this scan
   */
  CloseableIterable<T> planFiles();

  /**
   * Plan balanced task groups for this scan by splitting large and combining small tasks.
   * <p>
   * Task groups created by this method may read partial input files, multiple input files or both.
   *
   * @return an Iterable of balanced task groups required by this scan
   */
  CloseableIterable<G> planTasks();

  /**
   * Returns the target split size for this scan.
   */
  long targetSplitSize();

  /**
   * Returns the split lookback for this scan.
   */
  int splitLookback();

  /**
   * Returns the split open file cost for this scan.
   */
  long splitOpenFileCost();
}