Map over Key instead of actual instances when deleting old commit logs

Attempting to run DeleteOldCommitLogs in prod resulted in a lot of DatastoreTimeoutException errors. The assumption is that attempting to load so many CommitLogManifests (over 200 million of them), when each one has a slight possibility of failure, has a very high probability of error.

The shard aborts after 20 of these errors, and by eliminating as many loads as possible and retrying the remaining loads inside a transaction we are effectively eliminating any exceptions "leaking" out to the mapreduce framework, which will hopefully keep us bellow 20. At least, that's our best guess currently as to why the mapreduce fails.

EppResources are loaded in the map stage to get the revisions, and CommitLogManifests are only loaded in the reduce stage for sanity check so we don't accidentally delete resources we need in prod. Both of these are wrapped in transactNew to make sure they retry individually.

The only "load" not done inside a transaction is the EppResourceIndex, but there's no getting around that without rewriting the EppResourceInputs.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=164176764

java/google/registry/backup/DeleteOldCommitLogsAction.java

@@ -14,6 +14,8 @@
 
 package google.registry.backup;
 
+import static com.google.common.base.Preconditions.checkNotNull;
+import static com.google.common.base.Preconditions.checkState;
 import static google.registry.mapreduce.MapreduceRunner.PARAM_DRY_RUN;
 import static google.registry.model.ofy.ObjectifyService.ofy;
 import static google.registry.util.FormattingLogger.getLoggerForCallerClass;
@@ -33,7 +35,6 @@ import google.registry.mapreduce.MapreduceRunner;
 import google.registry.mapreduce.inputs.CommitLogManifestInput;
 import google.registry.mapreduce.inputs.EppResourceInputs;
 import google.registry.model.EppResource;
-import google.registry.model.ImmutableObject;
 import google.registry.model.ofy.CommitLogManifest;
 import google.registry.model.ofy.CommitLogMutation;
 import google.registry.model.translators.CommitLogRevisionsTranslatorFactory;
@@ -98,7 +99,7 @@ public final class DeleteOldCommitLogsAction implements Runnable {
               new DeleteOldCommitLogsReducer(deletionThreshold, isDryRun),
               ImmutableList.of(
                   new CommitLogManifestInput(Optional.of(deletionThreshold)),
-                  EppResourceInputs.createEntityInput(EppResource.class)))));
+                  EppResourceInputs.createKeyInput(EppResource.class)))));
   }
 
   /**
@@ -110,29 +111,52 @@ public final class DeleteOldCommitLogsAction implements Runnable {
    * <p>The reducer will then delete all CommitLogRevisions that only have {@code true}.
    */
   private static class DeleteOldCommitLogsMapper
-      extends Mapper<ImmutableObject, Key<CommitLogManifest>, Boolean> {
+      extends Mapper<Key<?>, Key<CommitLogManifest>, Boolean> {
 
     private static final long serialVersionUID = -1960845380164573834L;
 
+    private static final String KIND_MANIFEST = Key.getKind(CommitLogManifest.class);
+
     @Override
-    public void map(ImmutableObject object) {
-      if (object instanceof EppResource) {
-        getContext().incrementCounter("Epp resources found");
-        EppResource eppResource = (EppResource) object;
-        for (Key<CommitLogManifest> manifestKey : eppResource.getRevisions().values()) {
-          emit(manifestKey, false);
-        }
-        getContext()
-            .incrementCounter("Epp resource revisions found", eppResource.getRevisions().size());
-      } else if (object instanceof CommitLogManifest) {
+    public void map(final Key<?> key) {
+      // key is either a Key<CommitLogManifest> or a Key<? extends EppResource>.
+      //
+      // If it's a CommitLogManifest we just emit it as is (no need to load it).
+      if (key.getKind().equals(KIND_MANIFEST)) {
         getContext().incrementCounter("old commit log manifests found");
-        emit(Key.create((CommitLogManifest) object), true);
-      } else {
-        throw new IllegalArgumentException(
-            String.format(
-                "Received object of type %s, expected either EppResource or CommitLogManifest",
-                object.getClass().getName()));
+        // safe because we checked getKind
+        @SuppressWarnings("unchecked")
+        Key<CommitLogManifest> manifestKey = (Key<CommitLogManifest>) key;
+        emit(manifestKey, true);
+        return;
       }
+
+      // If it isn't a Key<CommitLogManifest> then it should be an EppResource, which we need to
+      // load to emit the revisions.
+      //
+      // We want to make sure we retry any load individually to reduce the chance of the entire
+      // shard failing, hence we wrap it in a transactNew.
+      Object object = ofy().transactNew(new Work<Object>() {
+        @Override
+        public Object run() {
+          return ofy().load().key(key).now();
+        }
+      });
+      checkNotNull(object, "Received a key to a missing object. key: %s", key);
+      checkState(
+          object instanceof EppResource,
+          "Received a key to an object that isn't EppResource nor CommitLogManifest."
+          + " Key: %s object type: %s",
+          key,
+          object.getClass().getName());
+
+      getContext().incrementCounter("EPP resources found");
+      EppResource eppResource = (EppResource) object;
+      for (Key<CommitLogManifest> manifestKey : eppResource.getRevisions().values()) {
+        emit(manifestKey, false);
+      }
+      getContext()
+          .incrementCounter("EPP resource revisions found", eppResource.getRevisions().size());
     }
   }
 
@@ -165,14 +189,17 @@ public final class DeleteOldCommitLogsAction implements Runnable {
         getContext().incrementCounter("old commit log manifests still referenced");
         return;
       }
-      if (ofy().load().key(manifestKey).now().getCommitTime().isAfter(deletionThreshold)) {
-        logger.severefmt("Won't delete CommitLogManifest %s that is too recent.", manifestKey);
-        getContext().incrementCounter("manifests incorrectly assigned for deletion (SEE LOGS)");
-        return;
-      }
-      Integer deletedCount = ofy().transact(new Work<Integer>() {
+
+      Integer deletedCount = ofy().transactNew(new Work<Integer>() {
         @Override
         public Integer run() {
+          // Doing a sanity check on the date. This is the only place we load the CommitLogManifest,
+          // so maybe removing this test will improve performance. However, unless it's proven that
+          // the performance boost is significant (and we've tested this enough to be sure it never
+          // happens)- the safty of "let's not delete stuff we need from prod" is more important.
+          if (ofy().load().key(manifestKey).now().getCommitTime().isAfter(deletionThreshold)) {
+            return 0;
+          }
           Iterable<Key<CommitLogMutation>> commitLogMutationKeys = ofy().load()
               .type(CommitLogMutation.class)
               .ancestor(manifestKey)
@@ -190,8 +217,14 @@ public final class DeleteOldCommitLogsAction implements Runnable {
           return keysToDelete.size();
         }
       });
-      getContext().incrementCounter("old commit log manifests deleted");
-      getContext().incrementCounter("total entities deleted", deletedCount);
+
+      if (deletedCount > 0) {
+        getContext().incrementCounter("old commit log manifests deleted");
+        getContext().incrementCounter("total entities deleted", deletedCount);
+      } else {
+        logger.severefmt("Won't delete CommitLogManifest %s that is too recent.", manifestKey);
+        getContext().incrementCounter("manifests incorrectly assigned for deletion (SEE LOGS)");
+      }
     }
   }
 }