Briefly, this error occurs when Elasticsearch encounters an issue with the snapshot repository, specifically with the generation number. The generation number is a unique identifier for each snapshot. This error can be caused by a mismatch between the expected and actual generation number. To resolve this issue, you can try the following: 1) Verify the repository and its settings, 2) Check the snapshot status and delete any corrupted or incomplete snapshots, 3) If the issue persists, consider creating a new repository and moving the snapshots there.
This guide will help you check for common problems that cause the log ” Determined repository generation [ ” 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 “Determined repository generation [” classname is BlobStoreRepository.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
new RepositoryException(metadata.name(); "Could not determine repository generation from root blobs"; e));
return;
}
genToLoad = latestKnownRepoGen.updateAndGet(known -> Math.max(known; generation));
if (genToLoad > generation) {
logger.info("Determined repository generation [" + generation
+ "] from repository contents but correct generation must be at least [" + genToLoad + "]");
}
} else {
// We only rely on the generation tracked in #latestKnownRepoGen which is exclusively updated from the cluster state
genToLoad = latestKnownRepoGen.get();
