Updated: July-20
Elasticsearch Version: 1.7-8.0
Before you begin reading this guide, we recommend you try running the Elasticsearch Error Check-Up which can resolve issues causing many errors
This guide will help you check for common problems that cause the log “concurrent modification of the index-N file; expected current generation” to appear. It’s important to understand the issues related to the log, so to get started, read the general overview on common issues and tips related to the Elasticsearch concepts: repositories, blobstore.
Advanced users might want to skip right to the common problems section in each concept or try running the Check-Up which analyses ES to discover the cause of many errors and provides suitable actionable recommendations (free tool that requires no installation).
Repository in Elasticsearch
What it is
An Elasticsearch snapshot provides a backup mechanism that takes the current state and data in the cluster and saves it to a repository (read the Glossary term 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 per cluster can be created. 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 a repository of type fs:
PUT _snapshot/my_repo_01
{
"type": "fs",
"settings": {
"location": "/mnt/my_repo_dir"
}
}
Notes and common problems
- S3, HDFS , Azure and Google Cloud requires 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 in case you are planning to use repo type of file system otherwise it will fail
- In case of 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 in partial snapshots.
Log Context
Log”concurrent modification of the index-N file; expected current generation [“classname is BlobStoreRepository.java
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
// snapshot delete run anyway.
logger.debug("Determined repository's generation from its contents to [" + generation + "] but " +
"current generation is at least [" + genToLoad + "]");
}
if (genToLoad != repositoryStateId) {
throw new RepositoryException(metadata.name(); "concurrent modification of the index-N file; expected current generation [" +
repositoryStateId + "]; actual current generation [" + genToLoad + "]");
}
if (cached != null && cached.v1() == genToLoad) {
return repositoryDataFromCachedEntry(cached);
}
Related issues to this log
We have gathered selected Q&A from the community and issues from Github, that can help fix related issues please review the following for further information :
1 Causes of getting a java.lang.VerifyError -views 292,207 ,score 191
2 Illegal character in path at index 16 -views 194,436,score 38
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