Fixes inefficient loading of snapshot repository data (#24510)

This commit fixes inefficient (worst case exponential) loading of 
snapshot repository data when checking for incompatible snapshots,
that was introduced in #22267.  When getting snapshot information,
getRepositoryData() was called on every snapshot, so if there are
a large number of snapshots in the repository and _all snapshots
were requested, the performance degraded exponentially.  This
commit fixes the issue by only calling getRepositoryData once and
using the data from it in all subsequent calls to get snapshot 
information.

Closes #24509

core/src/main/java/org/elasticsearch/action/admin/cluster/snapshots/get/TransportGetSnapshotsAction.java

@@ -30,6 +30,7 @@
 import org.elasticsearch.common.inject.Inject;
 import org.elasticsearch.common.regex.Regex;
 import org.elasticsearch.common.settings.Settings;
+import org.elasticsearch.repositories.RepositoryData;
 import org.elasticsearch.snapshots.SnapshotId;
 import org.elasticsearch.snapshots.SnapshotInfo;
 import org.elasticsearch.snapshots.SnapshotMissingException;
@@ -82,13 +83,14 @@ protected void masterOperation(final GetSnapshotsRequest request, ClusterState s
             List<SnapshotInfo> snapshotInfoBuilder = new ArrayList<>();
             final Map<String, SnapshotId> allSnapshotIds = new HashMap<>();
             final List<SnapshotId> currentSnapshotIds = new ArrayList<>();
+            final RepositoryData repositoryData  = snapshotsService.getRepositoryData(repository);
             for (SnapshotInfo snapshotInfo : snapshotsService.currentSnapshots(repository)) {
                 SnapshotId snapshotId = snapshotInfo.snapshotId();
                 allSnapshotIds.put(snapshotId.getName(), snapshotId);
                 currentSnapshotIds.add(snapshotId);
             }
             if (isCurrentSnapshotsOnly(request.snapshots()) == false) {
-                for (SnapshotId snapshotId : snapshotsService.getRepositoryData(repository).getAllSnapshotIds()) {
+                for (SnapshotId snapshotId : repositoryData.getAllSnapshotIds()) {
                     allSnapshotIds.put(snapshotId.getName(), snapshotId);
                 }
             }
@@ -119,7 +121,8 @@ protected void masterOperation(final GetSnapshotsRequest request, ClusterState s
                 }
             }
 
-            snapshotInfoBuilder.addAll(snapshotsService.snapshots(repository, new ArrayList<>(toResolve), request.ignoreUnavailable()));
+            snapshotInfoBuilder.addAll(snapshotsService.snapshots(
+                repository, new ArrayList<>(toResolve), repositoryData.getIncompatibleSnapshotIds(), request.ignoreUnavailable()));
             listener.onResponse(new GetSnapshotsResponse(snapshotInfoBuilder));
         } catch (Exception e) {
             listener.onFailure(e);

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

@@ -490,15 +490,6 @@ public MetaData getSnapshotMetaData(SnapshotInfo snapshot, List<IndexId> indices
 
     @Override
     public SnapshotInfo getSnapshotInfo(final SnapshotId snapshotId) {
-        if (getRepositoryData().getIncompatibleSnapshotIds().contains(snapshotId)) {
-            // an incompatible snapshot - cannot read its snapshot metadata file, just return
-            // a SnapshotInfo indicating its incompatible
-            return SnapshotInfo.incompatible(snapshotId);
-        }
-        return getSnapshotInfoInternal(snapshotId);
-    }
-
-    private SnapshotInfo getSnapshotInfoInternal(final SnapshotId snapshotId) {
         try {
             return snapshotFormat.read(snapshotsBlobContainer, snapshotId.getUUID());
         } catch (NoSuchFileException ex) {

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

@@ -164,11 +164,15 @@ public SnapshotInfo snapshot(final String repositoryName, final SnapshotId snaps
      *
      * @param repositoryName repository name
      * @param snapshotIds       snapshots for which to fetch snapshot information
+     * @param incompatibleSnapshotIds   snapshots for which not to fetch snapshot information
      * @param ignoreUnavailable if true, snapshots that could not be read will only be logged with a warning,
      *                          if false, they will throw an error
      * @return list of snapshots
      */
-    public List<SnapshotInfo> snapshots(final String repositoryName, List<SnapshotId> snapshotIds, final boolean ignoreUnavailable) {
+    public List<SnapshotInfo> snapshots(final String repositoryName,
+                                        final List<SnapshotId> snapshotIds,
+                                        final List<SnapshotId> incompatibleSnapshotIds,
+                                        final boolean ignoreUnavailable) {
         final Set<SnapshotInfo> snapshotSet = new HashSet<>();
         final Set<SnapshotId> snapshotIdsToIterate = new HashSet<>(snapshotIds);
         // first, look at the snapshots in progress
@@ -182,7 +186,13 @@ public List<SnapshotInfo> snapshots(final String repositoryName, List<SnapshotId
         final Repository repository = repositoriesService.repository(repositoryName);
         for (SnapshotId snapshotId : snapshotIdsToIterate) {
             try {
-                snapshotSet.add(repository.getSnapshotInfo(snapshotId));
+                if (incompatibleSnapshotIds.contains(snapshotId)) {
+                    // an incompatible snapshot - cannot read its snapshot metadata file, just return
+                    // a SnapshotInfo indicating its incompatible
+                    snapshotSet.add(SnapshotInfo.incompatible(snapshotId));
+                } else {
+                    snapshotSet.add(repository.getSnapshotInfo(snapshotId));
+                }
             } catch (Exception ex) {
                 if (ignoreUnavailable) {
                     logger.warn((Supplier<?>) () -> new ParameterizedMessage("failed to get snapshot [{}]", snapshotId), ex);