[GitHub] [iceberg] nastra commented on a diff in pull request #7880: Core: Add View support

["nastra (via GitHub)" <gi...@apache.org>]

nastra commented on code in PR #7880:
URL: https://github.com/apache/iceberg/pull/7880#discussion_r1239494785


##########
core/src/main/java/org/apache/iceberg/view/BaseViewOperations.java:
##########
@@ -0,0 +1,212 @@
+/*
+ * 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.view;
+
+import java.util.UUID;
+import java.util.concurrent.atomic.AtomicReference;
+import java.util.function.Function;
+import java.util.function.Predicate;
+import org.apache.iceberg.exceptions.AlreadyExistsException;
+import org.apache.iceberg.exceptions.CommitFailedException;
+import org.apache.iceberg.exceptions.NoSuchViewException;
+import org.apache.iceberg.exceptions.NotFoundException;
+import org.apache.iceberg.io.OutputFile;
+import org.apache.iceberg.relocated.com.google.common.base.Objects;
+import org.apache.iceberg.util.Tasks;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public abstract class BaseViewOperations implements ViewOperations {
+  private static final Logger LOG = LoggerFactory.getLogger(BaseViewOperations.class);
+
+  private static final String METADATA_FOLDER_NAME = "metadata";
+
+  private ViewMetadata currentMetadata = null;
+  private String currentMetadataLocation = null;
+  private boolean shouldRefresh = true;
+  private int version = -1;
+
+  protected BaseViewOperations() {}
+
+  protected void requestRefresh() {
+    this.shouldRefresh = true;
+  }
+
+  protected void disableRefresh() {
+    this.shouldRefresh = false;
+  }
+
+  protected void doRefresh() {
+    throw new UnsupportedOperationException("Not implemented: doRefresh");
+  }
+
+  protected void doCommit(ViewMetadata base, ViewMetadata metadata) {
+    throw new UnsupportedOperationException("Not implemented: doCommit");
+  }
+
+  protected abstract String viewName();
+
+  public int currentVersion() {
+    return version;
+  }
+
+  public String currentMetadataLocation() {
+    return currentMetadataLocation;
+  }
+
+  @Override
+  public ViewMetadata current() {
+    if (shouldRefresh) {
+      return refresh();
+    }
+
+    return currentMetadata;
+  }
+
+  @Override
+  public ViewMetadata refresh() {
+    boolean currentMetadataWasAvailable = currentMetadata != null;
+    try {
+      doRefresh();
+    } catch (NoSuchViewException e) {
+      if (currentMetadataWasAvailable) {
+        LOG.warn("Could not find the view during refresh, setting current metadata to null", e);
+        shouldRefresh = true;
+      }
+
+      currentMetadata = null;
+      currentMetadataLocation = null;
+      version = -1;
+      throw e;
+    }
+
+    return current();
+  }
+
+  @Override
+  public void commit(ViewMetadata base, ViewMetadata metadata) {
+    // if the metadata is already out of date, reject it
+    if (base != current()) {
+      if (base != null) {
+        throw new CommitFailedException("Cannot commit: stale view metadata");
+      } else {
+        // when current is non-null, the view exists. but when base is null, the commit is trying
+        // to create the view
+        throw new AlreadyExistsException("View already exists: %s", viewName());
+      }
+    }
+
+    // if the metadata is not changed, return early
+    if (base == metadata) {
+      LOG.info("Nothing to commit.");
+      return;
+    }
+
+    long start = System.currentTimeMillis();
+    doCommit(base, metadata);
+    requestRefresh();
+
+    LOG.info(
+        "Successfully committed to view {} in {} ms",
+        viewName(),
+        System.currentTimeMillis() - start);
+  }
+
+  protected String writeNewMetadata(ViewMetadata metadata, int newVersion) {
+    String newMetadataFilePath = newMetadataFilePath(metadata, newVersion);
+    OutputFile newMetadataLocation = io().newOutputFile(newMetadataFilePath);
+
+    // write the new metadata
+    // use overwrite to avoid negative caching in S3. this is safe because the metadata location is
+    // always unique because it includes a UUID.
+    ViewMetadataParser.overwrite(metadata, newMetadataLocation);
+
+    return newMetadataLocation.location();
+  }
+
+  private String newMetadataFilePath(ViewMetadata metadata, int newVersion) {
+    return metadataFileLocation(
+        metadata, String.format("%05d-%s%s", newVersion, UUID.randomUUID(), ".metadata.json"));
+  }
+
+  private String metadataFileLocation(ViewMetadata metadata, String filename) {
+    return String.format("%s/%s/%s", metadata.location(), METADATA_FOLDER_NAME, filename);
+  }
+
+  protected void refreshFromMetadataLocation(String newLocation) {
+    refreshFromMetadataLocation(newLocation, null, 20);
+  }
+
+  protected void refreshFromMetadataLocation(
+      String newLocation, Predicate<Exception> shouldRetry, int numRetries) {
+    refreshFromMetadataLocation(
+        newLocation,
+        shouldRetry,
+        numRetries,
+        metadataLocation -> ViewMetadataParser.read(io().newInputFile(metadataLocation)));
+  }
+
+  protected void refreshFromMetadataLocation(
+      String newLocation,
+      Predicate<Exception> shouldRetry,
+      int numRetries,
+      Function<String, ViewMetadata> metadataLoader) {
+    if (!Objects.equal(currentMetadataLocation, newLocation)) {
+      LOG.info("Refreshing view metadata from new version: {}", newLocation);
+
+      AtomicReference<ViewMetadata> newMetadata = new AtomicReference<>();
+      Tasks.foreach(newLocation)
+          .retry(numRetries)
+          .exponentialBackoff(100, 5000, 600000, 4.0 /* 100, 400, 1600, ... */)
+          .throwFailureWhenFinished()
+          .stopRetryOn(NotFoundException.class) // overridden if shouldRetry is non-null
+          .shouldRetryTest(shouldRetry)
+          .run(metadataLocation -> newMetadata.set(metadataLoader.apply(metadataLocation)));
+
+      this.currentMetadata = newMetadata.get();
+      this.currentMetadataLocation = newLocation;
+      this.version = parseVersion(newLocation);
+    }
+
+    this.shouldRefresh = false;
+  }
+
+  /**
+   * Parse the version from view metadata file name.
+   *
+   * @param metadataLocation view metadata file location
+   * @return version of the view metadata file in success case and -1 if the version is not parsable
+   *     (as a sign that the metadata is not part of this catalog)
+   */
+  private static int parseVersion(String metadataLocation) {

Review Comment:
   there are a few things in this class that are code duplicates of `BaseMetastoreTableOperations` so we might want to consider refactoring this out and make it re-usable



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