How To Solve Issues Related to Log – Updating flush-threshold-period from to

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Last update: Feb-20

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Troubleshooting Background – start here to get the full picture       
Related Issues – selected resources on related issues  
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Troubleshooting background

To troubleshoot Elasticsearch log “Updating flush-threshold-period from to” it’s important to know common problems related to Elasticsearch concepts: index. See below-detailed explanations complete with common problems, examples and useful tips.

Index in Elasticsearch

What it is

In Elasticsearch, an index (indices in plural) can be thought of as a table inside a database that has a schema and can have one or more shards and replicas. An Elasticsearch index is divided into shards and each shard is an instance of a Lucene index.

Indices are used to store the documents in dedicated data structures corresponding to the data type of fields. For example, text fields are stored inside an inverted index whereas numeric and geo fields are stored inside BKD trees.

Examples
Create Index

The following example is based on Elasticsearch version 5.x onwards. An index with two shards, each having one replica will be created with the name test_index1

PUT /test_index1?pretty
{
    "settings" : {
        "number_of_shards" : 2,
        "number_of_replicas" : 1
    },
    "mappings" : {
        "properties" : {
            "tags" : { "type" : "keyword" },
            "updated_at" : { "type" : "date" }
        }
    }
}
List Indices

All the index names and their basic information can be retrieved using the following command:

GET _cat/indices?v
Index a document

Let’s add a document in the index with below command:

PUT test_index1/_doc/1
{
  "tags": [
    "opster",
    "elasticsearch"
  ],
  "date": "01-01-2020"
}
Query an index
GET test_index1/_search
{
  "query": {
    "match_all": {}
  }
}
Query Multiple Indices

It is possible to search multiple indices with a single request. If it is a raw HTTP request, Index names should be sent in comma-separated format, as shown in the example below, and in the case of a query via a programming language client such as python or Java, index names are to be sent in a list format.

GET test_index1,test_index2/_search
Delete Indices
DELETE test_index1
Common Problems
  • It is good practice to define the settings and mapping of an Index wherever possible because if this is not done, Elasticsearch tries to automatically guess the data type of fields at the time of indexing. This automatic process may have disadvantages, such as mapping conflicts, duplicate data and incorrect data types being set in the index. If the fields are not known in advance, it’s better to use dynamic index templates.
  • Elasticsearch supports wildcard patterns in Index names, which sometimes aids with querying multiple indices, but can also be very destructive too. For example, It is possible to delete all the indices in a single command using the following commands:
DELETE /*

To disable this, you can add the following lines in the elasticsearch.yml:

action.destructive_requires_name: true

Threshold in Elasticsearch

What it is

Elasticsearch uses several parameters to enable it to manage hard disk storage across the cluster

What it’s used for
  • Elasticsearch will actively try to relocate shards away from nodes which exceed the disk watermark high threshold.
  • Elasticsearch will NOT locate new shards or relocate shards on to nodes which exceed the disk watermark low threshold.
  • Elasticsearch will prevent all writes to an index which has any shard on a node that exceeds the disk.watermark.flood_stage threshold.
  • The info update interval is the time it will take Elasticsearch to re-check the disk usage
Examples
PUT _cluster/settings
{
  "transient": {
   
    "cluster.routing.allocation.disk.watermark.low": "85%",
    "cluster.routing.allocation.disk.watermark.high": "90%",
    "cluster.routing.allocation.disk.watermark.flood_stage": "95%",
    "cluster.info.update.interval": "1m"
  }
}
Notes and good things to know:
  • ou can use absolute values eg.”100gb” or percentages eg. “90%”, but you cannot mix the two on the same cluster. 
  • In general, it is recommended to use percentages, since this will work in cases where disks are resized.
  • You can put the cluster settings on the elasticsearch.yml on each node,  but it is recommended to use the PUT _cluster/settings API because it is easier to manage, and ensures that the settings are coherent across the cluster.
  • Elasticsearch comes with sensible defaults for these settings, so think twice before modifying them.  If you find you are spending a lot of time fine-tuning these settings, then it is probably time to invest in new disk space.
  • In the event of the flood_stage.the threshold being exceeded, once you delete data, Elasticsearch should detect automatically that the block can be released (bearing in mind the update interval which could be, for instance, a minute).  However if you want to accelerate this process, you can unblock an index manually, with the following call 
PUT /my_index/_settings
{
  "index.blocks.read_only_allow_delete": null
}
Common problems

Inappropriate cluster settings (if the disk watermark.low is too low) can make it impossible for Elasticsearch to allocate shards on the cluster.  In particular, bear in mind that these parameters work in combination with other cluster settings (for example shard allocation awareness) which cause further restraints on how elasticsearch can allocate shards.


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. Migration Plugin How To Change Dyna  

2. Github Issue Number 765      


Log Context

Log ”Updating flush-threshold-period from to” classname is TranslogService.java
We have extracted the following from Elasticsearch source code to get an in-depth context :

                 logger.info("updating flush_threshold_size from [{}] to [{}]"; TranslogService.this.flushThresholdSize; flushThresholdSize);
                TranslogService.this.flushThresholdSize = flushThresholdSize;
            }
            TimeValue flushThresholdPeriod = settings.getAsTime(INDEX_TRANSLOG_FLUSH_THRESHOLD_PERIOD; TranslogService.this.flushThresholdPeriod);
            if (!flushThresholdPeriod.equals(TranslogService.this.flushThresholdPeriod)) {
                logger.info("updating flush_threshold_period from [{}] to [{}]"; TranslogService.this.flushThresholdPeriod; flushThresholdPeriod);
                TranslogService.this.flushThresholdPeriod = flushThresholdPeriod;
            }
            TimeValue interval = settings.getAsTime(INDEX_TRANSLOG_FLUSH_INTERVAL; TranslogService.this.interval);
            if (!interval.equals(TranslogService.this.interval)) {
                logger.info("updating interval from [{}] to [{}]"; TranslogService.this.interval; interval);






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