diff --git a/core/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java b/core/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java index 9469ac8b50983..01bd5e8a81888 100644 --- a/core/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java +++ b/core/src/main/java/org/elasticsearch/common/settings/ClusterSettings.java @@ -366,7 +366,6 @@ public void apply(Settings value, Settings current, Settings previous) { Node.NODE_INGEST_SETTING, Node.NODE_ATTRIBUTES, URLRepository.ALLOWED_URLS_SETTING, - URLRepository.REPOSITORIES_LIST_DIRECTORIES_SETTING, URLRepository.REPOSITORIES_URL_SETTING, URLRepository.SUPPORTED_PROTOCOLS_SETTING, TransportMasterNodeReadAction.FORCE_LOCAL_SETTING, diff --git a/core/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java b/core/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java index c1efcb7801cf4..52372706d34cb 100644 --- a/core/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java +++ b/core/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java @@ -24,6 +24,7 @@ import org.elasticsearch.Version; import org.elasticsearch.cluster.metadata.IndexMetaData; import org.elasticsearch.cluster.metadata.MetaData; +import org.elasticsearch.common.Numbers; import org.elasticsearch.snapshots.SnapshotId; import org.elasticsearch.common.ParseFieldMatcher; import org.elasticsearch.common.Strings; @@ -34,7 +35,6 @@ import org.elasticsearch.common.blobstore.BlobStore; import org.elasticsearch.common.bytes.BytesArray; import org.elasticsearch.common.bytes.BytesReference; -import org.elasticsearch.common.collect.Tuple; import org.elasticsearch.common.component.AbstractLifecycleComponent; import org.elasticsearch.common.compress.NotXContentException; import org.elasticsearch.common.io.Streams; @@ -83,7 +83,8 @@ * 
  * {@code
  *   STORE_ROOT
- *   |- index             - list of all snapshot name as JSON array
+ *   |- index-N           - list of all snapshot name as JSON array, N is the generation of the file
+ *   |- index-latest      - contains the numeric value of the latest generation of the index file (i.e. N from above)
  *   |- snapshot-20131010 - JSON serialized Snapshot for snapshot "20131010"
  *   |- meta-20131010.dat - JSON serialized MetaData for snapshot "20131010" (includes only global metadata)
  *   |- snapshot-20131011 - JSON serialized Snapshot for snapshot "20131011"
@@ -127,12 +128,14 @@ public abstract class BlobStoreRepository extends AbstractLifecycleComponent snapshotIds = snapshots().stream().filter(id -> snapshotId.equals(id) == false).collect(Collectors.toList());
-            writeSnapshotList(snapshotIds);
+            writeSnapshotsToIndexGen(snapshotIds);
+
             // Now delete all indices
             for (String index : indices) {
                 BlobPath indexPath = basePath().add("indices").add(index);
@@ -386,8 +389,8 @@ public SnapshotInfo finalizeSnapshot(final SnapshotId snapshotId,
                 snapshotIds = new ArrayList<>(snapshotIds);
                 snapshotIds.add(snapshotId);
                 snapshotIds = Collections.unmodifiableList(snapshotIds);
+                writeSnapshotsToIndexGen(snapshotIds);
             }
-            writeSnapshotList(snapshotIds);
             return blobStoreSnapshot;
         } catch (IOException ex) {
             throw new RepositoryException(this.repositoryName, "failed to update snapshot in repository", ex);
@@ -400,40 +403,12 @@ public SnapshotInfo finalizeSnapshot(final SnapshotId snapshotId,
     @Override
     public List snapshots() {
         try {
-            List snapshots = new ArrayList<>();
-            Map blobs;
-            try {
-                blobs = snapshotsBlobContainer.listBlobsByPrefix(COMMON_SNAPSHOT_PREFIX);
-            } catch (UnsupportedOperationException ex) {
-                // Fall back in case listBlobsByPrefix isn't supported by the blob store
-                return readSnapshotList();
-            }
-            int prefixLength = SNAPSHOT_PREFIX.length();
-            int suffixLength = SNAPSHOT_SUFFIX.length();
-            int legacyPrefixLength = LEGACY_SNAPSHOT_PREFIX.length();
-            for (BlobMetaData md : blobs.values()) {
-                String blobName = md.name();
-                final String name;
-                String uuid;
-                if (blobName.startsWith(SNAPSHOT_PREFIX) && blobName.length() > legacyPrefixLength) {
-                    final String str = blobName.substring(prefixLength, blobName.length() - suffixLength);
-                    // TODO: this will go away once we make the snapshot file writes atomic and
-                    // use it as the source of truth for the snapshots list instead of listing blobs
-                    Tuple pair = parseNameUUIDFromBlobName(str);
-                    name = pair.v1();
-                    uuid = pair.v2();
-                } else if (blobName.startsWith(LEGACY_SNAPSHOT_PREFIX) && blobName.length() > suffixLength + prefixLength) {
-                    name = blobName.substring(legacyPrefixLength);
-                    uuid = SnapshotId.UNASSIGNED_UUID;
-                } else {
-                    // not sure what it was - ignore
-                    continue;
-                }
-                snapshots.add(new SnapshotId(name, uuid));
-            }
-            return Collections.unmodifiableList(snapshots);
-        } catch (IOException ex) {
-            throw new RepositoryException(repositoryName, "failed to list snapshots in repository", ex);
+            return Collections.unmodifiableList(readSnapshotsFromIndex());
+        } catch (NoSuchFileException | FileNotFoundException e) {
+            // its a fresh repository, no index file exists, so return an empty list
+            return Collections.emptyList();
+        } catch (IOException ioe) {
+            throw new RepositoryException(repositoryName, "failed to list snapshots in repository", ioe);
         }
     }
 
@@ -564,89 +539,6 @@ private BlobStoreFormat indexMetaDataFormat(Version version) {
     private static final String NAME = "name";
     private static final String UUID = "uuid";
 
-    /**
-     * Writes snapshot index file
-     * 

-     * This file can be used by read-only repositories that are unable to list files in the repository
-     *
-     * @param snapshots list of snapshot ids
-     * @throws IOException I/O errors
-     */
-    protected void writeSnapshotList(List snapshots) throws IOException {
-        final BytesReference bRef;
-        try(BytesStreamOutput bStream = new BytesStreamOutput()) {
-            try(StreamOutput stream = new OutputStreamStreamOutput(bStream)) {
-                XContentBuilder builder = XContentFactory.contentBuilder(XContentType.JSON, stream);
-                builder.startObject();
-                builder.startArray(SNAPSHOTS);
-                for (SnapshotId snapshot : snapshots) {
-                    builder.startObject();
-                    builder.field(NAME, snapshot.getName());
-                    builder.field(UUID, snapshot.getUUID());
-                    builder.endObject();
-                }
-                builder.endArray();
-                builder.endObject();
-                builder.close();
-            }
-            bRef = bStream.bytes();
-        }
-        if (snapshotsBlobContainer.blobExists(SNAPSHOTS_FILE)) {
-            snapshotsBlobContainer.deleteBlob(SNAPSHOTS_FILE);
-        }
-        snapshotsBlobContainer.writeBlob(SNAPSHOTS_FILE, bRef);
-    }
-
-    /**
-     * Reads snapshot index file
-     * 

-     * This file can be used by read-only repositories that are unable to list files in the repository
-     *
-     * @return list of snapshots in the repository
-     * @throws IOException I/O errors
-     */
-    protected List readSnapshotList() throws IOException {
-        try (InputStream blob = snapshotsBlobContainer.readBlob(SNAPSHOTS_FILE)) {
-            BytesStreamOutput out = new BytesStreamOutput();
-            Streams.copy(blob, out);
-            ArrayList snapshots = new ArrayList<>();
-            try (XContentParser parser = XContentHelper.createParser(out.bytes())) {
-                if (parser.nextToken() == XContentParser.Token.START_OBJECT) {
-                    if (parser.nextToken() == XContentParser.Token.FIELD_NAME) {
-                        String currentFieldName = parser.currentName();
-                        if (SNAPSHOTS.equals(currentFieldName)) {
-                            if (parser.nextToken() == XContentParser.Token.START_ARRAY) {
-                                while (parser.nextToken() != XContentParser.Token.END_ARRAY) {
-                                    // the new format from 5.0 which contains the snapshot name and uuid
-                                    String name = null;
-                                    String uuid = null;
-                                    if (parser.currentToken() == XContentParser.Token.START_OBJECT) {
-                                        while (parser.nextToken() != XContentParser.Token.END_OBJECT) {
-                                            currentFieldName = parser.currentName();
-                                            parser.nextToken();
-                                            if (NAME.equals(currentFieldName)) {
-                                                name = parser.text();
-                                            } else if (UUID.equals(currentFieldName)) {
-                                                uuid = parser.text();
-                                            }
-                                        }
-                                        snapshots.add(new SnapshotId(name, uuid));
-                                    }
-                                    // the old format pre 5.0 that only contains the snapshot name, use the name as the uuid too
-                                    else {
-                                        name = parser.text();
-                                        snapshots.add(new SnapshotId(name, SnapshotId.UNASSIGNED_UUID));
-                                    }
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-            return Collections.unmodifiableList(snapshots);
-        }
-    }
-
     @Override
     public void onRestorePause(long nanos) {
         restoreRateLimitingTimeInNanos.inc(nanos);
@@ -714,27 +606,99 @@ BlobContainer blobContainer() {
         return snapshotsBlobContainer;
     }
 
-    // TODO: this will go away once readSnapshotsList uses the index file instead of listing blobs
-    // to know which snapshots are part of a repository.  See #18156
-    // Package private for testing.
-    static Tuple parseNameUUIDFromBlobName(final String str) {
-        final String name;
-        final String uuid;
-        final int sizeOfUUID = 22; // uuid is 22 chars in length
-        // unreliable, but highly unlikely to have a snapshot name with a dash followed by 22 characters,
-        // and this will go away before a release (see #18156).
-        //norelease
-        if (str.length() > sizeOfUUID + 1 && str.charAt(str.length() - sizeOfUUID - 1) == '-') {
-            // new naming convention, snapshot blob id has name and uuid
-            final int idx = str.length() - sizeOfUUID - 1;
-            name = str.substring(0, idx);
-            uuid = str.substring(idx + 1);
+    protected void writeSnapshotsToIndexGen(final List snapshots) throws IOException {
+        assert readOnly() == false; // can not write to a read only repository
+        final BytesReference snapshotsBytes;
+        try (BytesStreamOutput bStream = new BytesStreamOutput()) {
+            try (StreamOutput stream = new OutputStreamStreamOutput(bStream)) {
+                XContentBuilder builder = XContentFactory.contentBuilder(XContentType.JSON, stream);
+                builder.startObject();
+                builder.startArray(SNAPSHOTS);
+                for (SnapshotId snapshot : snapshots) {
+                    builder.startObject();
+                    builder.field(NAME, snapshot.getName());
+                    builder.field(UUID, snapshot.getUUID());
+                    builder.endObject();
+                }
+                builder.endArray();
+                builder.endObject();
+                builder.close();
+            }
+            snapshotsBytes = bStream.bytes();
+        }
+        final long gen = latestIndexBlobId() + 1;
+        // write the index file
+        writeAtomic(SNAPSHOTS_FILE_PREFIX + Long.toString(gen), snapshotsBytes);
+        // delete the N-2 index file if it exists, keep the previous one around as a backup
+        if (readOnly() == false && gen - 2 >= 0) {
+            final String oldSnapshotIndexFile = SNAPSHOTS_FILE_PREFIX + Long.toString(gen - 2);
+            if (snapshotsBlobContainer.blobExists(oldSnapshotIndexFile)) {
+                snapshotsBlobContainer.deleteBlob(oldSnapshotIndexFile);
+            }
+        }
+
+        // write the current generation to the index-latest file
+        final BytesReference genBytes;
+        try (BytesStreamOutput bStream = new BytesStreamOutput()) {
+            bStream.writeLong(gen);
+            genBytes = bStream.bytes();
+        }
+        if (snapshotsBlobContainer.blobExists(SNAPSHOTS_INDEX_LATEST_BLOB)) {
+            snapshotsBlobContainer.deleteBlob(SNAPSHOTS_INDEX_LATEST_BLOB);
+        }
+        writeAtomic(SNAPSHOTS_INDEX_LATEST_BLOB, genBytes);
+    }
+
+    protected List readSnapshotsFromIndex() throws IOException {
+        final long indexGen = latestIndexBlobId();
+        final String snapshotsIndexBlobName;
+        if (indexGen == -1) {
+            // index-N file doesn't exist, either its a fresh repository, or its in the
+            // old format, so look for the older index file before returning an empty list
+            snapshotsIndexBlobName = SNAPSHOTS_FILE;
         } else {
-            // old naming convention, before snapshots had UUIDs
-            name = str;
-            uuid = SnapshotId.UNASSIGNED_UUID;
+            snapshotsIndexBlobName = SNAPSHOTS_FILE_PREFIX + Long.toString(indexGen);
+        }
+
+        try (InputStream blob = snapshotsBlobContainer.readBlob(snapshotsIndexBlobName)) {
+            BytesStreamOutput out = new BytesStreamOutput();
+            Streams.copy(blob, out);
+            ArrayList snapshots = new ArrayList<>();
+            try (XContentParser parser = XContentHelper.createParser(out.bytes())) {
+                if (parser.nextToken() == XContentParser.Token.START_OBJECT) {
+                    if (parser.nextToken() == XContentParser.Token.FIELD_NAME) {
+                        String currentFieldName = parser.currentName();
+                        if (SNAPSHOTS.equals(currentFieldName)) {
+                            if (parser.nextToken() == XContentParser.Token.START_ARRAY) {
+                                while (parser.nextToken() != XContentParser.Token.END_ARRAY) {
+                                    // the new format from 5.0 which contains the snapshot name and uuid
+                                    String name = null;
+                                    String uuid = null;
+                                    if (parser.currentToken() == XContentParser.Token.START_OBJECT) {
+                                        while (parser.nextToken() != XContentParser.Token.END_OBJECT) {
+                                            currentFieldName = parser.currentName();
+                                            parser.nextToken();
+                                            if (NAME.equals(currentFieldName)) {
+                                                name = parser.text();
+                                            } else if (UUID.equals(currentFieldName)) {
+                                                uuid = parser.text();
+                                            }
+                                        }
+                                        snapshots.add(new SnapshotId(name, uuid));
+                                    }
+                                    // the old format pre 5.0 that only contains the snapshot name, use the name as the uuid too
+                                    else {
+                                        name = parser.text();
+                                        snapshots.add(new SnapshotId(name, SnapshotId.UNASSIGNED_UUID));
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+            return Collections.unmodifiableList(snapshots);
         }
-        return Tuple.tuple(name, uuid);
     }
 
     // Package private for testing
@@ -746,4 +710,79 @@ static String blobId(final SnapshotId snapshotId) {
         }
         return snapshotId.getName() + "-" + uuid;
     }
+
+    /**
+     * Get the latest snapshot index blob id.  Snapshot index blobs are named index-N, where N is
+     * the next version number from when the index blob was written.  Each individual index-N blob is
+     * only written once and never overwritten.  The highest numbered index-N blob is the latest one
+     * that contains the current snapshots in the repository.
+     *
+     * Package private for testing
+     */
+    long latestIndexBlobId() throws IOException {
+        try {
+            // first, try listing the blobs and determining which index blob is the latest
+            return listBlobsToGetLatestIndexId();
+        } catch (UnsupportedOperationException e) {
+            // could not list the blobs because the repository does not support the operation,
+            // try reading from the index-latest file
+            try {
+                return readSnapshotIndexLatestBlob();
+            } catch (IOException ioe) {
+                // we likely could not find the blob, this can happen in two scenarios:
+                //  (1) its an empty repository
+                //  (2) when writing the index-latest blob, if the blob already exists,
+                //      we first delete it, then atomically write the new blob.  there is
+                //      a small window in time when the blob is deleted and the new one
+                //      written - if the node crashes during that time, we won't have an
+                //      index-latest blob
+                // in a read-only repository, we can't know which of the two scenarios it is,
+                // but we will assume (1) because we can't do anything about (2) anyway
+                return -1;
+            }
+        }
+    }
+
+    // package private for testing
+    long readSnapshotIndexLatestBlob() throws IOException {
+        try (InputStream blob = snapshotsBlobContainer.readBlob(SNAPSHOTS_INDEX_LATEST_BLOB)) {
+            BytesStreamOutput out = new BytesStreamOutput();
+            Streams.copy(blob, out);
+            return Numbers.bytesToLong(out.bytes().toBytesRef());
+        }
+    }
+
+    private long listBlobsToGetLatestIndexId() throws IOException {
+        Map blobs = snapshotsBlobContainer.listBlobsByPrefix(SNAPSHOTS_FILE_PREFIX);
+        long latest = -1;
+        if (blobs.isEmpty()) {
+            // no snapshot index blobs have been written yet
+            return latest;
+        }
+        for (final BlobMetaData blobMetaData : blobs.values()) {
+            final String blobName = blobMetaData.name();
+            try {
+                final long curr = Long.parseLong(blobName.substring(SNAPSHOTS_FILE_PREFIX.length()));
+                latest = Math.max(latest, curr);
+            } catch (NumberFormatException nfe) {
+                // the index- blob wasn't of the format index-N where N is a number,
+                // no idea what this blob is but it doesn't belong in the repository!
+                logger.debug("[{}] Unknown blob in the repository: {}", repositoryName, blobName);
+            }
+        }
+        return latest;
+    }
+
+    private void writeAtomic(final String blobName, final BytesReference bytesRef) throws IOException {
+        final String tempBlobName = "pending-" + blobName;
+        snapshotsBlobContainer.writeBlob(tempBlobName, bytesRef);
+        try {
+            snapshotsBlobContainer.move(tempBlobName, blobName);
+        } catch (IOException ex) {
+            // Move failed - try cleaning up
+            snapshotsBlobContainer.deleteBlob(tempBlobName);
+            throw ex;
+        }
+    }
+
 }
diff --git a/core/src/main/java/org/elasticsearch/repositories/uri/URLRepository.java b/core/src/main/java/org/elasticsearch/repositories/uri/URLRepository.java
index b805727fd9c9d..0eb3006c5c3c2 100644
--- a/core/src/main/java/org/elasticsearch/repositories/uri/URLRepository.java
+++ b/core/src/main/java/org/elasticsearch/repositories/uri/URLRepository.java
@@ -19,7 +19,6 @@
 
 package org.elasticsearch.repositories.uri;
 
-import org.elasticsearch.snapshots.SnapshotId;
 import org.elasticsearch.common.blobstore.BlobPath;
 import org.elasticsearch.common.blobstore.BlobStore;
 import org.elasticsearch.common.blobstore.url.URLBlobStore;
@@ -42,7 +41,6 @@
 import java.util.Collections;
 import java.util.List;
 import java.util.function.Function;
-import java.util.function.Predicate;
 
 /**
  * Read-only URL-based implementation of the BlobStoreRepository
@@ -69,11 +67,6 @@ public class URLRepository extends BlobStoreRepository {
         new Setting<>("repositories.url.url", (s) -> s.get("repositories.uri.url", "http:"), URLRepository::parseURL,
             Property.NodeScope);
 
-    public static final Setting LIST_DIRECTORIES_SETTING =
-        Setting.boolSetting("list_directories", true, Property.NodeScope);
-    public static final Setting REPOSITORIES_LIST_DIRECTORIES_SETTING =
-        Setting.boolSetting("repositories.uri.list_directories", true, Property.NodeScope);
-
     private final List supportedProtocols;
 
     private final URIPattern[] urlWhiteList;
@@ -84,8 +77,6 @@ public class URLRepository extends BlobStoreRepository {
 
     private final BlobPath basePath;
 
-    private boolean listDirectories;
-
     /**
      * Constructs new read-only URL-based repository
      *
@@ -103,7 +94,6 @@ public URLRepository(RepositoryName name, RepositorySettings repositorySettings,
         supportedProtocols = SUPPORTED_PROTOCOLS_SETTING.get(settings);
         urlWhiteList = ALLOWED_URLS_SETTING.get(settings).toArray(new URIPattern[]{});
         this.environment = environment;
-        listDirectories = LIST_DIRECTORIES_SETTING.exists(repositorySettings.settings()) ? LIST_DIRECTORIES_SETTING.get(repositorySettings.settings()) : REPOSITORIES_LIST_DIRECTORIES_SETTING.get(settings);
 
         URL url = URL_SETTING.exists(repositorySettings.settings()) ? URL_SETTING.get(repositorySettings.settings()) : REPOSITORIES_URL_SETTING.get(settings);
         URL normalizedURL = checkURL(url);
@@ -124,19 +114,6 @@ protected BlobPath basePath() {
         return basePath;
     }
 
-    @Override
-    public List snapshots() {
-        if (listDirectories) {
-            return super.snapshots();
-        } else {
-            try {
-                return readSnapshotList();
-            } catch (IOException ex) {
-                throw new RepositoryException(repositoryName, "failed to get snapshot list in repository", ex);
-            }
-        }
-    }
-
     /**
      * Makes sure that the url is white listed or if it points to the local file system it matches one on of the root path in path.repo
      */
diff --git a/core/src/test/java/org/elasticsearch/repositories/blobstore/BlobStoreRepositoryTests.java b/core/src/test/java/org/elasticsearch/repositories/blobstore/BlobStoreRepositoryTests.java
index 3d46c0bbacf58..17e2481b7d05b 100644
--- a/core/src/test/java/org/elasticsearch/repositories/blobstore/BlobStoreRepositoryTests.java
+++ b/core/src/test/java/org/elasticsearch/repositories/blobstore/BlobStoreRepositoryTests.java
@@ -24,7 +24,6 @@
 import org.elasticsearch.client.Client;
 import org.elasticsearch.common.UUIDs;
 import org.elasticsearch.common.bytes.BytesReference;
-import org.elasticsearch.common.collect.Tuple;
 import org.elasticsearch.common.io.stream.BytesStreamOutput;
 import org.elasticsearch.common.io.stream.OutputStreamStreamOutput;
 import org.elasticsearch.common.io.stream.StreamOutput;
@@ -46,7 +45,6 @@
 import java.util.stream.Collectors;
 
 import static org.elasticsearch.repositories.blobstore.BlobStoreRepository.blobId;
-import static org.elasticsearch.repositories.blobstore.BlobStoreRepository.parseNameUUIDFromBlobName;
 import static org.hamcrest.Matchers.equalTo;
 
 /**
@@ -108,26 +106,13 @@ public void testRetrieveSnapshots() throws Exception {
         assertThat(snapshotIds, equalTo(originalSnapshots));
     }
 
-    public void testSnapshotIndexFile() throws Exception {
-        final Client client = client();
-        final Path location = ESIntegTestCase.randomRepoPath(node().settings());
-        final String repositoryName = "test-repo";
-
-        PutRepositoryResponse putRepositoryResponse =
-            client.admin().cluster().preparePutRepository(repositoryName)
-                                    .setType("fs")
-                                    .setSettings(Settings.builder().put(node().settings()).put("location", location))
-                                    .get();
-        assertThat(putRepositoryResponse.isAcknowledged(), equalTo(true));
-
-        final RepositoriesService repositoriesService = getInstanceFromNode(RepositoriesService.class);
-        @SuppressWarnings("unchecked") final BlobStoreRepository repository =
-            (BlobStoreRepository) repositoriesService.repository(repositoryName);
+    public void testReadAndWriteSnapshotsThroughIndexFile() throws Exception {
+        final BlobStoreRepository repository = setupRepo();
 
         // write to and read from a snapshot file with no entries
-        repository.writeSnapshotList(Collections.emptyList());
-        List readSnapshotIds = repository.readSnapshotList();
-        assertThat(readSnapshotIds.size(), equalTo(0));
+        assertThat(repository.snapshots().size(), equalTo(0));
+        repository.writeSnapshotsToIndexGen(Collections.emptyList());
+        assertThat(repository.snapshots().size(), equalTo(0));
 
         // write to and read from a snapshot file with a random number of entries
         final int numSnapshots = randomIntBetween(1, 1000);
@@ -135,26 +120,43 @@ public void testSnapshotIndexFile() throws Exception {
         for (int i = 0; i < numSnapshots; i++) {
             snapshotIds.add(new SnapshotId(randomAsciiOfLength(8), UUIDs.randomBase64UUID()));
         }
-        repository.writeSnapshotList(snapshotIds);
-        readSnapshotIds = repository.readSnapshotList();
-        assertThat(readSnapshotIds, equalTo(snapshotIds));
+        repository.writeSnapshotsToIndexGen(snapshotIds);
+        assertThat(repository.snapshots(), equalTo(snapshotIds));
     }
 
-    public void testOldIndexFileFormat() throws Exception {
-        final Client client = client();
-        final Path location = ESIntegTestCase.randomRepoPath(node().settings());
-        final String repositoryName = "test-repo";
+    public void testIndexGenerationalFiles() throws Exception {
+        final BlobStoreRepository repository = setupRepo();
 
-        PutRepositoryResponse putRepositoryResponse =
-            client.admin().cluster().preparePutRepository(repositoryName)
-                .setType("fs")
-                .setSettings(Settings.builder().put(node().settings()).put("location", location))
-                .get();
-        assertThat(putRepositoryResponse.isAcknowledged(), equalTo(true));
+        // write to index generational file
+        final int numSnapshots = randomIntBetween(1, 1000);
+        final List snapshotIds = new ArrayList<>(numSnapshots);
+        for (int i = 0; i < numSnapshots; i++) {
+            snapshotIds.add(new SnapshotId(randomAsciiOfLength(8), UUIDs.randomBase64UUID()));
+        }
+        repository.writeSnapshotsToIndexGen(snapshotIds);
+        assertThat(Sets.newHashSet(repository.readSnapshotsFromIndex()), equalTo(Sets.newHashSet(snapshotIds)));
+        assertThat(repository.latestIndexBlobId(), equalTo(0L));
+        assertThat(repository.readSnapshotIndexLatestBlob(), equalTo(0L));
 
-        final RepositoriesService repositoriesService = getInstanceFromNode(RepositoriesService.class);
-        @SuppressWarnings("unchecked") final BlobStoreRepository repository =
-            (BlobStoreRepository) repositoriesService.repository(repositoryName);
+        // adding more and writing to a new index generational file
+        for (int i = 0; i < 10; i++) {
+            snapshotIds.add(new SnapshotId(randomAsciiOfLength(8), UUIDs.randomBase64UUID()));
+        }
+        repository.writeSnapshotsToIndexGen(snapshotIds);
+        assertThat(Sets.newHashSet(repository.readSnapshotsFromIndex()), equalTo(Sets.newHashSet(snapshotIds)));
+        assertThat(repository.latestIndexBlobId(), equalTo(1L));
+        assertThat(repository.readSnapshotIndexLatestBlob(), equalTo(1L));
+
+        // removing a snapshot adn writing to a new index generational file
+        snapshotIds.remove(0);
+        repository.writeSnapshotsToIndexGen(snapshotIds);
+        assertThat(Sets.newHashSet(repository.readSnapshotsFromIndex()), equalTo(Sets.newHashSet(snapshotIds)));
+        assertThat(repository.latestIndexBlobId(), equalTo(2L));
+        assertThat(repository.readSnapshotIndexLatestBlob(), equalTo(2L));
+    }
+
+    public void testOldIndexFileFormat() throws Exception {
+        final BlobStoreRepository repository = setupRepo();
 
         // write old index file format
         final int numOldSnapshots = randomIntBetween(1, 50);
@@ -163,36 +165,15 @@ public void testOldIndexFileFormat() throws Exception {
             snapshotIds.add(new SnapshotId(randomAsciiOfLength(8), SnapshotId.UNASSIGNED_UUID));
         }
         writeOldFormat(repository, snapshotIds.stream().map(SnapshotId::getName).collect(Collectors.toList()));
-        List readSnapshotIds = repository.readSnapshotList();
-        assertThat(Sets.newHashSet(readSnapshotIds), equalTo(Sets.newHashSet(snapshotIds)));
+        assertThat(Sets.newHashSet(repository.snapshots()), equalTo(Sets.newHashSet(snapshotIds)));
 
         // write to and read from a snapshot file with a random number of new entries added
         final int numSnapshots = randomIntBetween(1, 1000);
         for (int i = 0; i < numSnapshots; i++) {
             snapshotIds.add(new SnapshotId(randomAsciiOfLength(8), UUIDs.randomBase64UUID()));
         }
-        repository.writeSnapshotList(snapshotIds);
-        readSnapshotIds = repository.readSnapshotList();
-        assertThat(Sets.newHashSet(readSnapshotIds), equalTo(Sets.newHashSet(snapshotIds)));
-    }
-
-    public void testParseUUIDFromBlobName() {
-        String blobStr = "abc123";
-        Tuple pair = parseNameUUIDFromBlobName(blobStr);
-        assertThat(pair.v1(), equalTo(blobStr)); // snapshot name
-        assertThat(pair.v2(), equalTo(SnapshotId.UNASSIGNED_UUID)); // snapshot uuid
-        blobStr = "abcefghijklmnopqrstuvwxyz";
-        pair = parseNameUUIDFromBlobName(blobStr);
-        assertThat(pair.v1(), equalTo(blobStr));
-        assertThat(pair.v2(), equalTo(SnapshotId.UNASSIGNED_UUID));
-        blobStr = "abc123-xyz"; // not enough characters after '-' to have a uuid
-        pair = parseNameUUIDFromBlobName(blobStr);
-        assertThat(pair.v1(), equalTo(blobStr));
-        assertThat(pair.v2(), equalTo(SnapshotId.UNASSIGNED_UUID));
-        blobStr = "abc123-a1b2c3d4e5f6g7h8i9j0k1";
-        pair = parseNameUUIDFromBlobName(blobStr);
-        assertThat(pair.v1(), equalTo("abc123"));
-        assertThat(pair.v2(), equalTo("a1b2c3d4e5f6g7h8i9j0k1"));
+        repository.writeSnapshotsToIndexGen(snapshotIds);
+        assertThat(Sets.newHashSet(repository.snapshots()), equalTo(Sets.newHashSet(snapshotIds)));
     }
 
     public void testBlobId() {
@@ -208,6 +189,24 @@ public void testBlobId() {
         assertThat(blobId(snapshotId), equalTo("abc-123-" + uuid)); // snapshot name + '-' + uuid
     }
 
+    private BlobStoreRepository setupRepo() {
+        final Client client = client();
+        final Path location = ESIntegTestCase.randomRepoPath(node().settings());
+        final String repositoryName = "test-repo";
+
+        PutRepositoryResponse putRepositoryResponse =
+            client.admin().cluster().preparePutRepository(repositoryName)
+                                    .setType("fs")
+                                    .setSettings(Settings.builder().put(node().settings()).put("location", location))
+                                    .get();
+        assertThat(putRepositoryResponse.isAcknowledged(), equalTo(true));
+
+        final RepositoriesService repositoriesService = getInstanceFromNode(RepositoriesService.class);
+        @SuppressWarnings("unchecked") final BlobStoreRepository repository =
+            (BlobStoreRepository) repositoriesService.repository(repositoryName);
+        return repository;
+    }
+
     private void writeOldFormat(final BlobStoreRepository repository, final List snapshotNames) throws Exception {
         final BytesReference bRef;
         try (BytesStreamOutput bStream = new BytesStreamOutput()) {
diff --git a/core/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java b/core/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java
index 15623825887f5..a25c8e0593e55 100644
--- a/core/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java
+++ b/core/src/test/java/org/elasticsearch/snapshots/DedicatedClusterSnapshotRestoreIT.java
@@ -284,8 +284,8 @@ public void clusterStateProcessed(String source, ClusterState oldState, ClusterS
         countDownLatch.await();
     }
 
-    private static interface ClusterStateUpdater {
-        public ClusterState execute(ClusterState currentState) throws Exception;
+    private interface ClusterStateUpdater {
+        ClusterState execute(ClusterState currentState) throws Exception;
     }
 
     public void testSnapshotDuringNodeShutdown() throws Exception {
@@ -392,8 +392,11 @@ public void testSnapshotWithStuckNode() throws Exception {
 
         logger.info("--> making sure that snapshot no longer exists");
         assertThrows(client().admin().cluster().prepareGetSnapshots("test-repo").setSnapshots("test-snap").execute(), SnapshotMissingException.class);
-        // Subtract index file from the count
-        assertThat("not all files were deleted during snapshot cancellation", numberOfFilesBeforeSnapshot, equalTo(numberOfFiles(repo) - 1));
+        // Subtract three files that will remain in the repository:
+        //   (1) index-1
+        //   (2) index-0 (because we keep the previous version) and
+        //   (3) index-latest
+        assertThat("not all files were deleted during snapshot cancellation", numberOfFilesBeforeSnapshot, equalTo(numberOfFiles(repo) - 3));
         logger.info("--> done");
     }
 
diff --git a/core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java b/core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java
index 19b46710fea0a..e1efbdfaf81ae 100644
--- a/core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java
+++ b/core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java
@@ -818,8 +818,9 @@ public void testDeleteSnapshot() throws Exception {
 
         logger.info("--> delete the last snapshot");
         client.admin().cluster().prepareDeleteSnapshot("test-repo", lastSnapshot).get();
-        logger.info("--> make sure that number of files is back to what it was when the first snapshot was made");
-        assertThat(numberOfFiles(repo), equalTo(numberOfFiles[0]));
+        logger.info("--> make sure that number of files is back to what it was when the first snapshot was made, " +
+                    "plus one because one backup index-N file should remain");
+        assertThat(numberOfFiles(repo), equalTo(numberOfFiles[0] + 1));
     }
 
     public void testDeleteSnapshotWithMissingIndexAndShardMetadata() throws Exception {
diff --git a/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/blobstore/AzureBlobStore.java b/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/blobstore/AzureBlobStore.java
index 2809b8588f19d..510b6d20f0791 100644
--- a/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/blobstore/AzureBlobStore.java
+++ b/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/blobstore/AzureBlobStore.java
@@ -34,6 +34,7 @@
 import org.elasticsearch.repositories.RepositoryName;
 import org.elasticsearch.repositories.RepositorySettings;
 
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URISyntaxException;
@@ -127,7 +128,7 @@ public void deleteBlob(String container, String blob) throws URISyntaxException,
         this.client.deleteBlob(this.accountName, this.locMode, container, blob);
     }
 
-    public InputStream getInputStream(String container, String blob) throws URISyntaxException, StorageException
+    public InputStream getInputStream(String container, String blob) throws URISyntaxException, StorageException, IOException
     {
         return this.client.getInputStream(this.accountName, this.locMode, container, blob);
     }
diff --git a/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/storage/AzureStorageService.java b/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/storage/AzureStorageService.java
index 13db36aeb5a29..137ff20efbeac 100644
--- a/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/storage/AzureStorageService.java
+++ b/plugins/repository-azure/src/main/java/org/elasticsearch/cloud/azure/storage/AzureStorageService.java
@@ -29,6 +29,7 @@
 import org.elasticsearch.common.unit.ByteSizeValue;
 import org.elasticsearch.common.unit.TimeValue;
 
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URISyntaxException;
@@ -75,7 +76,7 @@ final class Storage {
     void deleteBlob(String account, LocationMode mode, String container, String blob) throws URISyntaxException, StorageException;
 
     InputStream getInputStream(String account, LocationMode mode, String container, String blob)
-        throws URISyntaxException, StorageException;
+        throws URISyntaxException, StorageException, IOException;
 
     OutputStream getOutputStream(String account, LocationMode mode, String container, String blob)
         throws URISyntaxException, StorageException;
diff --git a/plugins/repository-azure/src/test/java/org/elasticsearch/cloud/azure/storage/AzureStorageServiceMock.java b/plugins/repository-azure/src/test/java/org/elasticsearch/cloud/azure/storage/AzureStorageServiceMock.java
index 8160c560325ae..5d4f9c6f69b04 100644
--- a/plugins/repository-azure/src/test/java/org/elasticsearch/cloud/azure/storage/AzureStorageServiceMock.java
+++ b/plugins/repository-azure/src/test/java/org/elasticsearch/cloud/azure/storage/AzureStorageServiceMock.java
@@ -31,6 +31,8 @@
 
 import java.io.ByteArrayInputStream;
 import java.io.ByteArrayOutputStream;
+import java.io.FileNotFoundException;
+import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
 import java.net.URISyntaxException;
@@ -79,7 +81,10 @@ public void deleteBlob(String account, LocationMode mode, String container, Stri
     }
 
     @Override
-    public InputStream getInputStream(String account, LocationMode mode, String container, String blob) {
+    public InputStream getInputStream(String account, LocationMode mode, String container, String blob) throws IOException {
+        if (!blobExists(account, mode, container, blob)) {
+            throw new FileNotFoundException("missing blob [" + blob + "]");
+        }
         return new ByteArrayInputStream(blobs.get(blob).toByteArray());
     }