Cheaper snapshot-related toString() impls (#121283)

If the `MasterService` needs to log a create-snapshot task description
then it will call `CreateSnapshotTask#toString`, which today calls
`RepositoryData#toString` which is not overridden so ends up calling
`RepositoryData#hashCode`. This can be extraordinarily expensive in a
large repository. Worse, if there's masses of create-snapshot tasks to
execute then it'll do this repeatedly, because each one only ends up
yielding a short hex string so we don't reach the description length
limit very easily.

With this commit we provide a more efficient implementation of
`CreateSnapshotTask#toString` and also override
`RepositoryData#toString` to protect against some other caller running
into the same issue.

Author: DaveCTurner

docs/changelog/121283.yaml

@@ -0,0 +1,5 @@
+pr: 121283
+summary: Cheaper snapshot-related `toString()` impls
+area: Snapshot/Restore
+type: bug
+issues: []

server/src/internalClusterTest/java/org/elasticsearch/snapshots/SnapshotsServiceIT.java

@@ -17,10 +17,12 @@
 import org.elasticsearch.cluster.SnapshotDeletionsInProgress;
 import org.elasticsearch.cluster.metadata.IndexMetadata;
 import org.elasticsearch.cluster.service.ClusterService;
+import org.elasticsearch.cluster.service.MasterService;
 import org.elasticsearch.common.settings.Settings;
 import org.elasticsearch.snapshots.mockstore.MockRepository;
 import org.elasticsearch.test.ClusterServiceUtils;
 import org.elasticsearch.test.MockLog;
+import org.elasticsearch.test.junit.annotations.TestLogging;
 
 import java.util.List;
 import java.util.concurrent.TimeUnit;
@@ -223,4 +225,30 @@ public void testRerouteWhenShardSnapshotsCompleted() throws Exception {
         safeAwait(shardMovedListener);
         ensureGreen(indexName);
     }
+
+    @TestLogging(reason = "testing task description, logged at DEBUG", value = "org.elasticsearch.cluster.service.MasterService:DEBUG")
+    public void testCreateSnapshotTaskDescription() {
+        createIndexWithRandomDocs(randomIdentifier(), randomIntBetween(1, 5));
+        final var repositoryName = randomIdentifier();
+        createRepository(repositoryName, "mock");
+
+        final var snapshotName = randomIdentifier();
+        MockLog.assertThatLogger(
+            () -> createFullSnapshot(repositoryName, snapshotName),
+            MasterService.class,
+            new MockLog.SeenEventExpectation(
+                "executing cluster state update debug message",
+                MasterService.class.getCanonicalName(),
+                Level.DEBUG,
+                "executing cluster state update for [create_snapshot ["
+                    + snapshotName
+                    + "][CreateSnapshotTask{repository="
+                    + repositoryName
+                    + ", snapshot=*"
+                    + snapshotName
+                    + "*}]]"
+            )
+        );
+    }
+
 }

server/src/main/java/org/elasticsearch/repositories/RepositoryData.java

@@ -605,6 +605,11 @@ public int hashCode() {
         return Objects.hash(snapshotIds, snapshotsDetails, indices, indexSnapshots, shardGenerations, indexMetaDataGenerations);
     }
 
+    @Override
+    public String toString() {
+        return Strings.format("RepositoryData[uuid=%s,gen=%s]", uuid, genId);
+    }
+
     /**
      * Resolve the index name to the index id specific to the repository,
      * throwing an exception if the index could not be resolved.

server/src/main/java/org/elasticsearch/snapshots/SnapshotsService.java

@@ -3885,6 +3885,11 @@ public void onFailure(Exception e) {
             logSnapshotFailure("create", snapshot, e);
             listener.onFailure(e);
         }
+
+        @Override
+        public String toString() {
+            return "CreateSnapshotTask{repository=" + repository.getMetadata().name() + ", snapshot=" + snapshot + '}';
+        }
     }
 
     private static void logSnapshotFailure(String operation, Snapshot snapshot, Exception e) {

server/src/test/java/org/elasticsearch/repositories/RepositoryDataTests.java

@@ -40,9 +40,12 @@
 
 import static org.elasticsearch.repositories.RepositoryData.EMPTY_REPO_GEN;
 import static org.elasticsearch.repositories.RepositoryData.MISSING_UUID;
+import static org.hamcrest.Matchers.allOf;
 import static org.hamcrest.Matchers.containsInAnyOrder;
+import static org.hamcrest.Matchers.containsString;
 import static org.hamcrest.Matchers.equalTo;
 import static org.hamcrest.Matchers.greaterThan;
+import static org.hamcrest.Matchers.not;
 
 /**
  * Tests for the {@link RepositoryData} class.
@@ -430,6 +433,19 @@ public void testFailsIfMinVersionNotSatisfied() throws IOException {
         }
     }
 
+    public void testToString() {
+        final var repositoryData = generateRandomRepoData();
+        assertThat(
+            repositoryData.toString(),
+            allOf(
+                containsString("RepositoryData"),
+                containsString(repositoryData.getUuid()),
+                containsString(Long.toString(repositoryData.getGenId())),
+                not(containsString("@")) // not the default Object#toString which does a very expensive hashcode computation
+            )
+        );
+    }
+
     public static RepositoryData generateRandomRepoData() {
         final int numIndices = randomIntBetween(1, 30);
         final List<IndexId> indices = new ArrayList<>(numIndices);