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Briefly, this error occurs when Elasticsearch detects a discrepancy between the checksum of a file on the primary shard and its replica during the recovery process. This could be due to network issues, disk errors, or bugs. To resolve this, you can try the following: 1) Restart the Elasticsearch node, which will trigger a new recovery process. 2) Delete and recreate the corrupted replica shard. 3) Check for any underlying hardware or network issues that might be causing the corruption. Always ensure you have a backup of your data to prevent data loss.
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This guide will help you check for common problems that cause the log ” {} Remote file corruption on node {}; recovering {}. local checksum OK ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: recovery, indices, node.
Overview
In Elasticsearch, recovery refers to the process of recovering an index or shard when something goes wrong. There are many ways to recover an index or shard, such as by re-indexing the data from a backup / failover cluster to the current one, or by restoring from an Elasticsearch snapshot. Alternatively, Elasticsearch performs recoveries automatically, such as when a node restarts or disconnects and connects again. There is an API to check the updated status of index / shard recoveries.
GET /<index>/_recoveryGET /_recovery
In summary, recovery can happen in the following scenarios:
- Node startup or failure (local store recovery)
- Replication of primary shards to replica shards
- Relocation of a shard to a different node in the same cluster
- Restoring a snapshot
Examples
Getting recovery information about several indices:
GET my_index1 GET my_index2/_recovery
Notes and good things to know
- When a node is disconnected from the cluster, all of its shards go to an unassigned state. After a certain amount of time, the shards will be allocated somewhere else on other nodes. This setting determines the number of concurrent shards per node that will be recovered.
PUT _cluster/settings{"transient":{"cluster.routing.allocation.node_concurrent_recoveries":3}}- You can also control when to start recovery after a node disconnects. This is useful if the node just restarts, for example, because you may not want to initiate any recovery for such transient events.
PUT _all/_settings{"settings":{"index.unassigned.node_left.delayed_timeout":"6m"}}- Elasticsearch limits the speed that is allocated to recovery in order to avoid overloading the cluster. This setting can be updated to make the recovery faster or slower, depending on your requirements.
PUT _cluster/settings{"transient":{"indices.recovery.max_bytes_per_sec":"100mb"}}Overview
To put it simply, a node is a single server that is part of a cluster. Each node is assigned one or more roles, which describe the node’s responsibility and operations. Data nodes store the data, and participate in the cluster’s indexing and search capabilities, while master nodes are responsible for managing the cluster’s activities and storing the cluster state, including the metadata.
While it is possible to run several node instances of Elasticsearch on the same hardware, it’s considered a best practice to limit a server to a single running instance of Elasticsearch.
Nodes connect to each other and form a cluster by using a discovery method.
Roles
Master node
Master nodes are in charge of cluster-wide settings and changes – deleting or creating indices and fields, adding or removing nodes and allocating shards to nodes. Each cluster has a single master node that is elected from the master eligible nodes using a distributed consensus algorithm and is reelected if the current master node fails.
Coordinating (client) node
There is some confusion in the use of coordinating node terminology. Client nodes were removed from Elasticsearch after version 2.4 and became coordinating nodes.
Coordinating nodes are nodes that do not hold any configured role. They don’t hold data and are not part of the master eligible group nor execute ingest pipelines. Coordinating nodes serve incoming search requests and act as the query coordinator running query and fetch phases, sending requests to every node that holds a shard being queried. The coordinating node also distributes bulk indexing operations and route queries to shards based on the node’s responsiveness.
Log Context
Log “{} Remote file corruption on node {}; recovering {}. local checksum OK” classname is RecoverySourceHandler.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
throw localException;
} else { // corruption has happened on the way to replica
RemoteTransportException remoteException = new RemoteTransportException(
"File corruption occurred on recovery but checksums are ok"; null);
remoteException.addSuppressed(e);
logger.warn(() -> new ParameterizedMessage("{} Remote file corruption on node {}; recovering {}. local checksum OK";
shardId; request.targetNode(); mds); corruptIndexException);
throw remoteException;
}
}
throw e;
