Minor Rearrangements in Snapshot Code (#46652) (#46752)

Inlining one trivial single-use method and extracting the
stale shard path blob calculation to make the diff with #46250
more manageable.

server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java

@@ -1240,14 +1240,7 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent imp
                     .collect(Collectors.toSet());
                 final BlobStoreIndexShardSnapshots updatedSnapshots = new BlobStoreIndexShardSnapshots(newSnapshotsList);
                 indexShardSnapshotsFormat.writeAtomic(updatedSnapshots, shardContainer, indexGeneration);
-                // Delete all previous index-N, data- and meta-blobs and that are not referenced by the new index-N and temporary blobs
+                blobsToDelete = unusedBlobs(blobs, survivingSnapshotUUIDs, updatedSnapshots);
-                blobsToDelete = blobs.keySet().stream().filter(blob ->
-                    blob.startsWith(SNAPSHOT_INDEX_PREFIX)
-                        || (blob.startsWith(SNAPSHOT_PREFIX) && blob.endsWith(".dat")
-                            && survivingSnapshotUUIDs.contains(
-                                blob.substring(SNAPSHOT_PREFIX.length(), blob.length() - ".dat".length())) == false)
-                        || (blob.startsWith(DATA_BLOB_PREFIX) && updatedSnapshots.findNameFile(canonicalName(blob)) == null)
-                        || FsBlobContainer.isTempBlobName(blob)).collect(Collectors.toList());
             }
             try {
                 shardContainer.deleteBlobsIgnoringIfNotExists(blobsToDelete);
@@ -1262,6 +1255,20 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent imp
         }
     }
 
+    // Unused blobs are all previous index-, data- and meta-blobs and that are not referenced by the new index- as well as all
+    // temporary blobs
+    private static List<String> unusedBlobs(Map<String, BlobMetaData> blobs, Set<String> survivingSnapshotUUIDs,
+                                            BlobStoreIndexShardSnapshots updatedSnapshots) {
+        return blobs.keySet().stream().filter(blob ->
+            blob.startsWith(SNAPSHOT_INDEX_PREFIX)
+                || (blob.startsWith(SNAPSHOT_PREFIX) && blob.endsWith(".dat")
+                    && survivingSnapshotUUIDs.contains(
+                        blob.substring(SNAPSHOT_PREFIX.length(), blob.length() - ".dat".length())) == false)
+                || (blob.startsWith(DATA_BLOB_PREFIX) && updatedSnapshots.findNameFile(canonicalName(blob)) == null)
+                || FsBlobContainer.isTempBlobName(blob)).collect(Collectors.toList());
+    }
+
+
     /**
      * Loads information about shard snapshot
      */

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

@@ -153,7 +153,10 @@ public class SnapshotShardsService extends AbstractLifecycleComponent implements
             if ((previousSnapshots == null && currentSnapshots != null)
                 || (previousSnapshots != null && previousSnapshots.equals(currentSnapshots) == false)) {
                 synchronized (shardSnapshots) {
-                    processIndexShardSnapshots(currentSnapshots);
+                    cancelRemoved(currentSnapshots);
+                    if (currentSnapshots != null) {
+                        startNewSnapshots(currentSnapshots);
+                    }
                 }
             }
 
@@ -199,18 +202,6 @@ public class SnapshotShardsService extends AbstractLifecycleComponent implements
         }
     }
 
-    /**
-     * Checks if any new shards should be snapshotted on this node
-     *
-     * @param snapshotsInProgress Current snapshots in progress in cluster state
-     */
-    private void processIndexShardSnapshots(SnapshotsInProgress snapshotsInProgress) {
-        cancelRemoved(snapshotsInProgress);
-        if (snapshotsInProgress != null) {
-            startNewSnapshots(snapshotsInProgress);
-        }
-    }
-
     private void cancelRemoved(@Nullable SnapshotsInProgress snapshotsInProgress) {
         // First, remove snapshots that are no longer there
         Iterator<Map.Entry<Snapshot, Map<ShardId, IndexShardSnapshotStatus>>> it = shardSnapshots.entrySet().iterator();

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

@@ -103,7 +103,7 @@ import static org.elasticsearch.cluster.SnapshotsInProgress.completed;
  * the {@link #beginSnapshot(ClusterState, SnapshotsInProgress.Entry, boolean, ActionListener)} method kicks in and initializes
  * the snapshot in the repository and then populates list of shards that needs to be snapshotted in cluster state</li>
  * <li>Each data node is watching for these shards and when new shards scheduled for snapshotting appear in the cluster state, data nodes
- * start processing them through {@link SnapshotShardsService#processIndexShardSnapshots(SnapshotsInProgress)} method</li>
+ * start processing them through {@link SnapshotShardsService#startNewSnapshots} method</li>
  * <li>Once shard snapshot is created data node updates state of the shard in the cluster state using
  * the {@link SnapshotShardsService#sendSnapshotShardUpdate(Snapshot, ShardId, ShardSnapshotStatus)} method</li>
  * <li>When last shard is completed master node in {@link SnapshotShardsService#innerUpdateSnapshotState} method marks the snapshot