rdblue commented on code in PR #5268:
URL: https://github.com/apache/iceberg/pull/5268#discussion_r926037826


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api/src/main/java/org/apache/iceberg/metrics/ScanReport.java:
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@@ -0,0 +1,251 @@
+/*
+ * 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.metrics;
+
+import java.io.Serializable;
+import java.time.Duration;
+import java.util.concurrent.TimeUnit;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.expressions.Expression;
+import org.apache.iceberg.metrics.MetricsContext.Counter;
+import org.apache.iceberg.relocated.com.google.common.base.MoreObjects;
+import org.apache.iceberg.relocated.com.google.common.base.Preconditions;
+
+/**
+ * A Table Scan report that contains all relevant information from a Table 
Scan.
+ */
+public class ScanReport implements Serializable {
+
+  private final String tableName;
+  private final long snapshotId;
+  private final Expression filter;
+  private final Schema projection;
+  private final int matchingDataFiles;
+  private final int matchingDataManifests;
+  private final int totalDataManifestsRead;
+  private final int addedDataFiles;
+  private final int deletedDataFiles;
+  private final Duration totalPlanningDuration;
+  private final long totalFileSizeBytes;

Review Comment:
   I think we should change some of these metrics to be more easily understood 
by people that see them. To do that, I'd start by establishing some consistent 
terms that we should use. Here's what I'm thinking:
   * Use "manifest" to refer to a manifest file
   * Use "file" to refer to a content file
   * Use "data" and "delete" to specify whether a manifest/file contains data 
or deletes
   * Use "filtered" to count what was rejected by a filter
   * Use "scanned" to count what is actually read
   * Use "result" to count the data files that are turned into tasks for the 
scan (alternatively, we could count `fileTasks`?)
   
   I'm trying to avoid using the term "matching" for a couple of reasons. 
First, it isn't entirely clear what that means when talking about a data file 
because the filter evaluation results in data files that need to be read, but 
don't necessarily match the filter. Second, using "filtered" instead gives a 
clearer picture of what happened during planning, since "matching" isn't always 
a result. For example, delete files that match the filter might be used or 
might not match based on sequence number.
   
   Using those terms gives some additional consistency.
   
   * `dataManifests` / `deleteManifests` - the number of data/delete manifests 
in the snapshot's manifest list
   * `filteredDataManifests` / `filteredDeleteManifests` - the number of 
data/delete manifests rejected by the filter
   * `scannedDataManifests` / `scannedDeleteManifests` - the number of 
data/delete manifests that were actually read
   * `totalDataFiles` / `totalDeleteFiles` - the number of data/delete files in 
manifests that would be scanned (not actually scanned)
   * `filteredDataFiles` / `filteredDeleteFiles` - the number of data/delete 
files rejected by the filter
   * `indexedDeleteFiles` - the number of delete files that were loaded into 
the `DeleteFileIndex`
   * `resultDataFiles` - the number of data files that are selected to be read
   
   Does that sound reasonable?



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