Updated: Feb-20
Elasticsearch Version: 1.7-8.0Background
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To troubleshoot log “Cannot read metadata for snapshot” it’s important to understand a few problems related to Elasticsearch concepts blobstore, metadata, repositories, repository-azure, snapshot. See bellow important tips and explanations on these concepts
Metadata in Elasticsearch
What it is
Metadata in Elasticsearch refers to storing some additional information for each document. This is achieved using the specific metadata fields available in Elasticsearch. The default behavior of some of these metadata fields can be customized during mapping creation.
Examples
Using _meta meta-field for storing application-specific information with the mapping:
PUT /my_index?pretty
{
"mappings": {
"_meta": {
"domain": "security",
"release_information": {
"date": "18-01-2020",
"version": "7.5"
}
}
}
}
Notes
- In version 2.x, Elasticsearch had a total 13 meta fields available, which are: _index, _uid, _type, _id, _source, _size, _all, _field_names, _timestamp, _ttl, _parent, _routing, _meta
- In version 5.x, _timestamp and _ttl meta fields were removed.
- In version 6.x, the _parent meta field was removed.
- In version 7.x, _uid and _all meta fields were removed.
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”cannot read metadata for snapshot [{}]” classname is BlobStoreRepository.java
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
metaData = readSnapshotMetaData(snapshotId; snapshot.version(); indices; true);
} else {
metaData = readSnapshotMetaData(snapshotId; null; indices; true);
}
} catch (IOException | SnapshotException ex) {
logger.warn("cannot read metadata for snapshot [{}]"; ex; snapshotId);
}
try {
// Delete snapshot file first so we wouldn't end up with partially deleted snapshot that looks OK
if (snapshot != null) {
snapshotFormat(snapshot.version()).delete(snapshotsBlobContainer; snapshotId.getSnapshot());
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 :
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