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Ali Beyad
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Ensures cleanup of temporary index-* generational blobs during snapshotting (#21469)
Ensures pending index-* blobs are deleted when snapshotting. The index-* blobs are generational files that maintain the snapshots in the repository. To write these atomically, we first write a `pending-index-*` blob, then move it to `index-*`, which also deletes `pending-index-*` in case its not a file-system level move (e.g. S3 repositories) . For example, to write the 5th generation of the index blob for the repository, we would first write the bytes to `pending-index-5` and then move `pending-index-5` to `index-5`. It is possible that we fail after writing `pending-index-5`, but before moving it to `index-5` or deleting `pending-index-5`. In this case, we will have a dangling `pending-index-5` blob laying around. Since snapshot #5 would have failed, the next snapshot assumes a generation number of 5, so it tries to write to `index-5`, which first tries to write to `pending-index-5` before moving the blob to `index-5`. Since `pending-index-5` is leftover from the previous failure, the snapshot fails as it cannot overwrite this blob. This commit solves the problem by first, adding a UUID to the `pending-index-*` blobs, and secondly, strengthen the logic around failure to write the `index-*` generational blob to ensure pending files are deleted on cleanup. Closes #21462
1 parent 9faf05b commit a00b588

4 files changed

Lines changed: 68 additions & 8 deletions

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‎core/src/main/java/org/elasticsearch/common/blobstore/BlobContainer.java‎

Lines changed: 5 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -105,8 +105,11 @@ public interface BlobContainer {
105105
Map<String, BlobMetaData> listBlobsByPrefix(String blobNamePrefix) throws IOException;
106106

107107
/**
108-
* Atomically renames the source blob into the target blob. If the source blob does not exist or the
109-
* target blob already exists, an exception is thrown.
108+
* Renames the source blob into the target blob. If the source blob does not exist or the
109+
* target blob already exists, an exception is thrown. Atomicity of the move operation
110+
* can only be guaranteed on an implementation-by-implementation basis. The only current
111+
* implementation of {@link BlobContainer} for which atomicity can be guaranteed is the
112+
* {@link org.elasticsearch.common.blobstore.fs.FsBlobContainer}.
110113
*
111114
* @param sourceBlobName
112115
* The blob to rename.

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

Lines changed: 7 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -867,15 +867,17 @@ private long listBlobsToGetLatestIndexId() throws IOException {
867867
}
868868

869869
private void writeAtomic(final String blobName, final BytesReference bytesRef) throws IOException {
870-
final String tempBlobName = "pending-" + blobName;
870+
final String tempBlobName = "pending-" + blobName + "-" + UUIDs.randomBase64UUID();
871871
try (InputStream stream = bytesRef.streamInput()) {
872872
snapshotsBlobContainer.writeBlob(tempBlobName, stream, bytesRef.length());
873-
}
874-
try {
875873
snapshotsBlobContainer.move(tempBlobName, blobName);
876874
} catch (IOException ex) {
877-
// Move failed - try cleaning up
878-
snapshotsBlobContainer.deleteBlob(tempBlobName);
875+
// temporary blob creation or move failed - try cleaning up
876+
try {
877+
snapshotsBlobContainer.deleteBlob(tempBlobName);
878+
} catch (IOException e) {
879+
ex.addSuppressed(e);
880+
}
879881
throw ex;
880882
}
881883
}

‎core/src/test/java/org/elasticsearch/snapshots/SharedClusterSnapshotRestoreIT.java‎

Lines changed: 49 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2592,4 +2592,53 @@ public void testGetSnapshotsRequest() throws Exception {
25922592
waitForCompletion(repositoryName, inProgressSnapshot, TimeValue.timeValueSeconds(60));
25932593
}
25942594

2595+
public void testSnapshotSucceedsAfterSnapshotFailure() throws Exception {
2596+
logger.info("--> creating repository");
2597+
final Path repoPath = randomRepoPath();
2598+
assertAcked(client().admin().cluster().preparePutRepository("test-repo").setType("mock").setVerify(false).setSettings(
2599+
Settings.builder().put("location", repoPath).put("random_control_io_exception_rate", randomIntBetween(5, 20) / 100f)));
2600+
2601+
logger.info("--> indexing some data");
2602+
createIndex("test-idx");
2603+
ensureGreen();
2604+
final int numDocs = randomIntBetween(1, 5);
2605+
for (int i = 0; i < numDocs; i++) {
2606+
index("test-idx", "doc", Integer.toString(i), "foo", "bar" + i);
2607+
}
2608+
refresh();
2609+
assertThat(client().prepareSearch("test-idx").setSize(0).get().getHits().totalHits(), equalTo((long) numDocs));
2610+
2611+
logger.info("--> snapshot with potential I/O failures");
2612+
try {
2613+
CreateSnapshotResponse createSnapshotResponse =
2614+
client().admin().cluster().prepareCreateSnapshot("test-repo", "test-snap")
2615+
.setWaitForCompletion(true)
2616+
.setIndices("test-idx")
2617+
.get();
2618+
if (createSnapshotResponse.getSnapshotInfo().totalShards() != createSnapshotResponse.getSnapshotInfo().successfulShards()) {
2619+
assertThat(getFailureCount("test-repo"), greaterThan(0L));
2620+
assertThat(createSnapshotResponse.getSnapshotInfo().shardFailures().size(), greaterThan(0));
2621+
for (SnapshotShardFailure shardFailure : createSnapshotResponse.getSnapshotInfo().shardFailures()) {
2622+
assertThat(shardFailure.reason(), containsString("Random IOException"));
2623+
}
2624+
}
2625+
} catch (Exception ex) {
2626+
// sometimes, the snapshot will fail with a top level I/O exception
2627+
assertThat(ExceptionsHelper.stackTrace(ex), containsString("Random IOException"));
2628+
}
2629+
2630+
logger.info("--> snapshot with no I/O failures");
2631+
assertAcked(client().admin().cluster().preparePutRepository("test-repo-2").setType("mock").setVerify(false).setSettings(
2632+
Settings.builder().put("location", repoPath)));
2633+
CreateSnapshotResponse createSnapshotResponse =
2634+
client().admin().cluster().prepareCreateSnapshot("test-repo-2", "test-snap-2")
2635+
.setWaitForCompletion(true)
2636+
.setIndices("test-idx")
2637+
.get();
2638+
assertEquals(0, createSnapshotResponse.getSnapshotInfo().failedShards());
2639+
GetSnapshotsResponse getSnapshotsResponse = client().admin().cluster().prepareGetSnapshots("test-repo-2")
2640+
.addSnapshots("test-snap-2").get();
2641+
assertEquals(SnapshotState.SUCCESS, getSnapshotsResponse.getSnapshots().get(0).state());
2642+
}
2643+
25952644
}

‎core/src/test/java/org/elasticsearch/snapshots/mockstore/MockRepository.java‎

Lines changed: 7 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -313,14 +313,20 @@ public Map<String, BlobMetaData> listBlobsByPrefix(String blobNamePrefix) throws
313313

314314
@Override
315315
public void move(String sourceBlob, String targetBlob) throws IOException {
316+
// simulate a non-atomic move, since many blob container implementations
317+
// will not have an atomic move, and we should be able to handle that
316318
maybeIOExceptionOrBlock(targetBlob);
317-
super.move(sourceBlob, targetBlob);
319+
super.writeBlob(targetBlob, super.readBlob(sourceBlob), 0L);
320+
super.deleteBlob(sourceBlob);
318321
}
319322

320323
@Override
321324
public void writeBlob(String blobName, InputStream inputStream, long blobSize) throws IOException {
322325
maybeIOExceptionOrBlock(blobName);
323326
super.writeBlob(blobName, inputStream, blobSize);
327+
// for network based repositories, the blob may have been written but we may still
328+
// get an error with the client connection, so an IOException here simulates this
329+
maybeIOExceptionOrBlock(blobName);
324330
}
325331
}
326332
}

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