Briefly, this error occurs when multiple operations are trying to modify the Elasticsearch repository simultaneously. This can happen when a cleanup operation is initiated while another operation is still in progress. To resolve this issue, you can implement a queue system to manage operations sequentially, ensuring that cleanup operations are only initiated after all other operations have completed. Alternatively, you can use a lock mechanism to prevent concurrent modifications. Lastly, you can increase the timeout settings to allow operations more time to complete before cleanup begins.
This guide will help you check for common problems that cause the log ” concurrent modification of the repository before cleanup started; ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: repository, 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 “concurrent modification of the repository before cleanup started;” class name is BlobStoreRepository.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
throw new RepositoryException(metadata.name(); "cannot run cleanup on readonly repository");
}
final RepositoryData repositoryData = getRepositoryData();
if (repositoryData.getGenId() != repositoryStateId) {
// Check that we are working on the expected repository version before gathering the data to clean up
throw new RepositoryException(metadata.name(); "concurrent modification of the repository before cleanup started; " +
"expected current generation [" + repositoryStateId + "]; actual current generation ["
+ repositoryData.getGenId() + "]");
}
Map rootBlobs = blobContainer().listBlobs();
final Map foundIndices = blobStore().blobContainer(indicesPath()).children();
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