Briefly, this error occurs when Elasticsearch encounters an unexpected situation during its operations. The actual exception could be due to various reasons such as incorrect configurations, insufficient resources, or issues with the data. To resolve this, you can check the Elasticsearch logs for more detailed information about the exception. Ensure that your configurations are correct and that Elasticsearch has enough resources (like memory and disk space). If the issue is with the data, you may need to clean or reindex it. Always ensure your Elasticsearch version is up-to-date to avoid bugs that could cause exceptions.
This guide will help you check for common problems that cause the log ” actual Exception ” to appear. To understand the issues related to this log, read the explanation below about the following Elasticsearch concepts: replication.
Overview
Replication refers to storing a redundant copy of the data. Starting from version 7.x, Elasticsearch creates one primary shard with a replication factor set to 1. Replicas never get assigned to the same node on which primary shards are assigned, which means you should have at least two nodes in the cluster to assign the replicas. If a primary shard goes down, the replica automatically acts as a primary shard.
What it is used for
Replicas are used to provide high availability and failover. A higher number of replicas is also helpful for faster searches.
Examples
Update replica count
PUT /api-logs/_settings?pretty
{
"index" : {
"number_of_replicas" : 2
}
}Common problems
- By default, new replicas are not assigned to nodes with more than 85% disk usage. Instead, Elasticsearch throws a warning.
- Creating too many replicas may cause a problem if there are not enough resources available in the cluster.
Log Context
Log “actual Exception” classname is TransportReplicationAction.java.
We extracted the following from Elasticsearch source code for those seeking an in-depth context :
Releasables.close(indexShardReference);
try {
channel.sendResponse(t);
} catch (IOException responseException) {
logger.warn("failed to send error message back to client for action [{}]"; responseException; transportReplicaAction);
logger.warn("actual Exception"; t);
}
}
}
private void doFinish() {
