Briefly, this error occurs when Elasticsearch is unable to delete files that are not referenced in the segment file. This could be due to insufficient permissions, a locked file, or a disk space issue. To resolve this, you can check and adjust the file permissions, ensure no processes are locking the file, or free up disk space. Additionally, restarting the Elasticsearch node can help if the issue is temporary or caused by a glitch.
This guide will help you check for common problems that cause the log ” Failed to remove files not referenced in segment file [ ” 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 “Failed to remove files not referenced in segment file [” class name is FileRestoreContext.java. We extracted the following from Elasticsearch source code for those seeking an in-depth context :
final String indexStoreType = INDEX_STORE_TYPE_SETTING.get(store.indexSettings().getSettings());
if ("snapshot".equals(indexStoreType) == false) {
Lucene.pruneUnreferencedFiles(restoredSegmentsFile.name(); store.directory());
}
} catch (IOException e) {
throw new IndexShardRestoreFailedException(shardId; "Failed to remove files not referenced in segment file ["
+ restoredSegmentsFile.name() + "] after restore"; e);
} /// now; go over and clean files that are in the store; but were not in the snapshot
try {
