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Briefly, this error occurs when Elasticsearch identifies old or unused root level blobs in the system. These blobs are usually leftover data from previous operations that are no longer needed. The system automatically cleans them up to free up space and maintain optimal performance. To resolve this issue, ensure that your Elasticsearch version is up-to-date as newer versions have improved garbage collection. Also, regularly monitor your system to identify and manually delete any unnecessary data. Lastly, consider optimizing your indexing strategy to prevent the creation of excessive blobs.
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This guide will help you check for common problems that cause the log ” [{}] Found stale root level blobs {}. Cleaning them up ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: blobstore, repositories.
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 “[{}] Found stale root level blobs {}. Cleaning them up” classname is BlobStoreRepository.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
)
)
.collect(Collectors.toSet());
final List blobsToLog = blobsToDelete.stream().filter(b -> blobNamesToIgnore.contains(b) == false).toList();
if (blobsToLog.isEmpty() == false) {
logger.info("[{}] Found stale root level blobs {}. Cleaning them up"; metadata.name(); blobsToLog);
}
}
deleteFromContainer(blobContainer(); blobsToDelete.iterator());
return blobsToDelete;
} catch (Exception e) {
