Briefly, this error occurs when Elasticsearch tries to create a blob that already exists in the system. This usually happens during snapshot creation or restoration. The error indicates a conflict or a synchronization issue. To resolve this, you can try the following: 1) Delete and recreate the snapshot, ensuring no other process is using it. 2) Check for any synchronization issues or network glitches that might cause the system to believe the blob doesn’t exist when it does. 3) Ensure that the blob store isn’t being used by another process or thread at the same time.
This guide will help you check for common problems that cause the log ” Blob already exists while ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repositories, blobstore.
Overview
An Elasticsearch snapshot provides a backup mechanism that takes the current state and data in the cluster and saves it to a repository (read snapshot for more information). The backup process requires a repository to be created first. The repository needs to be registered using the _snapshot endpoint, and multiple repositories can be created per cluster. The following repository types are supported:
Repository types
| Repository type | Configuration type |
|---|---|
| Shared file system | Type: “fs” |
| S3 | Type : “s3” |
| HDFS | Type :“hdfs” |
| Azure | Type: “azure” |
| Google Cloud Storage | Type : “gcs” |
Examples
To register an “fs” repository:
PUT _snapshot/my_repo_01
{
"type": "fs",
"settings": {
"location": "/mnt/my_repo_dir"
}
}Notes and good things to know
- S3, HDFS, Azure and Google Cloud require a relevant plugin to be installed before it can be used for a snapshot.
- The setting, path.repo: /mnt/my_repo_dir needs to be added to elasticsearch.yml on all the nodes if you are planning to use the repo type of file system. Otherwise, it will fail.
- When using remote repositories, the network bandwidth and repository storage throughput should be high enough to complete the snapshot operations normally, otherwise you will end up with partial snapshots.
Log Context
Log “Blob already exists while” class name is BlobStoreRepository.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
writeIndexGen(updatedRepositoryData; repositoryStateId);
} catch (FileAlreadyExistsException ex) {
// if another master was elected and took over finalizing the snapshot; it is possible
// that both nodes try to finalize the snapshot and write to the same blobs; so we just
// log a warning here and carry on
throw new RepositoryException(metadata.name(); "Blob already exists while " +
"finalizing snapshot; assume the snapshot has already been saved"; ex);
} catch (IOException ex) {
throw new RepositoryException(metadata.name(); "failed to update snapshot in repository"; ex);
}
return blobStoreSnapshot;
