How To Solve Issues Related to Log – Actual Exception

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Updated: Feb-20

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Troubleshooting Background       
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Log Context
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Troubleshooting background

To troubleshoot Elasticsearch log “Actual Exception” it’s important to understand common problems related to Elasticsearch concepts: replication. See detailed explanations below complete with common problems, examples and useful tips.

Replication in Elasticsearch

What it is

Replication refers to storing the 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 on 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 replication count

PUT /api-logs/_settings?pretty
{
    "index" : {
        "number_of_replicas" : 2
    }
}
Common problems
  • By default, If free disk space usage reaches 85%, the replicas of newly created indices are not assigned on that node and Elasticsearch throws a warning.
  • Creating too many replicas may cause a problem if there are not enough resources available in the cluster. 

To help troubleshoot related issues we have gathered selected Q&A from the community and issues from Github , please review the following for further information :

1 Elasticsearch Net 7 1 0 Issue  

2 Querying Elasticsearch With Nest Er  

Log Context

Log ” actual Exception” classname is TransportReplicationAction.java
We have extracted the following from Elasticsearch source code to get 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() {
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