Elasticsearch Slow Logs

Searching and indexing are the two main request types in Elasticsearch, and enabling the Elasticsearch slow logs will help you identify the problematic indices. Configure slow logs thresholds in your Elasticsearch indices and monitor the slow search and index logs using Site24x7's AppLogs. Our exclusive dashboard helps you figure out the ideal queries for optimization.

Enabling Elasticsearch slow logs
Getting started with log management
Elasticsearch slow logs dashboard

Enabling Elasticsearch slow logs

By default, slow logs are disabled in Elasticsearch. To enable logging, you must configure the Elasticsearch index settings API and set a threshold value for slow search or index logs. There are three kinds of thresholds that you can define:

Index (index)
The query phase of the search (query)
The fetch phase of the search (fetch)

To enable logging for slow search logs:

Query and fetch are the two main phases of the search process, and you can set the threshold for both phases of the execution.

curl -X PUT "<Elasticsearch_domain>/<Index>/_settings?pretty" -H 'Content-Type: application/json' -d' {
 "index.search.slowlog.threshold.query.warn": "0ms",
 "index.search.slowlog.threshold.query.info": "0ms",
 "index.search.slowlog.threshold.query.debug": "0ms",
 "index.search.slowlog.threshold.query.trace": "0ms",
 "index.search.slowlog.threshold.fetch.warn": "0ms",
 "index.search.slowlog.threshold.fetch.info": "0ms",
 "index.search.slowlog.threshold.fetch.debug": "0ms",
 "index.search.slowlog.threshold.fetch.trace": "0ms"
}'

To enable logging for slow index logs:

curl -X PUT "<Elasticsearch_domain>/<Index>/_settings?pretty" -H 'Content-Type: application/json' -d' {
 "index.indexing.slowlog.threshold.index.warn": "0ms",
 "index.indexing.slowlog.threshold.index.info": "0ms",
 "index.indexing.slowlog.threshold.index.debug": "0ms",
 "index.indexing.slowlog.threshold.index.trace": "0ms",
 "index.indexing.slowlog.level": "trace",
 "index.indexing.slowlog.source": "1000"
}'

Make sure to specify your Elasticsearch_domain (Eg: localhost:9200) and Index in the above queries. If you want to enable these settings for all indices, use * or _all for the Index. Setting the threshold limit as 0ms will log everything and affect the performance as a result. Set the threshold limit appropriately, as any searching or indexing that takes longer than a set threshold will be logged.

Getting started with log management

Log in to your Site24x7 account.
Download and install the Site24x7 Server monitoring agent (Windows | Linux).
Go to Admin > AppLogs > Log Profile, and click Add Log Profile.

Profile Name: Enter a name for your Log Profile.
Choose the Log Type: Choose Elasticsearch slow logs from the drop-down menu.
Log Source: Choose Local File from the drop-down menu.
List of files to search for logs: Include the below files:
/var/log/elasticsearch/*_index_indexing_slowlog*.log
/var/log/elasticsearch/*_index_search_slowlog*.log

Select the server, and click Save.

Log pattern

[$DateTime:date$][$LogLevel$][index.$Type$.slowlog.$Phase$.$NodeId$] [$NodeName$] [$Index$]![$Shard$]! took[*], took_millis[$TimeTaken:number$], !type[*], id[*], routing[*],!!total_hits[$TotalHits:number$], types[$Types$], stats[$Stats$], search_type[$SearchType$], total_shards[$TotalShared:number$],! source[$Message$

This is the default pattern defined by Site24x7 for parsing Elasticsearch slow logs based on the sample mentioned below.

Sample logs

The following are sample logs for the index and search (fetch and query phase) slow logs:

[2022-09-18T01:28:13,358][WARN ][index.indexing.slowlog.index.Y37CmUvQSi2jgtzN_-6K1A] [esd6C] [10772528_2000326507563_2000550180009_16_202/Y37CmUvQSi2jgtzN_-6K1A] took[1.5ms], took_millis[1], type[-1], id[Jcvyl4ABjtHtfc2jfkMH], routing[0], source[{"2002351591637":"367550","2002681248211":563,"2002351591639":215,"_zl_secs_to_millis":197]

[2022-09-18T00:57:14,861][WARN ][index.search.slowlog.fetch.tWO5cHxMRrGW3VuwRhIwYQ] [esd2C] [10772528_-1_-1_21_864][3] took[85.3micros], took_millis[0], total_hits[3456], types[some_type], stats[], search_type[QUERY_THEN_FETCH], total_shards[195], source[{"query":{"query_string":{"query":"*"}},"from":0,"size":"24","sort":{"updated_at":"desc"}}], extra_source[],

[2022-09-18T02:19:14,861][WARN ][index.search.slowlog.query.tWO5cHxMRrGW3VuwRhIwYQ] [esd2C] [10772528_-1_-1_21_864][0] took[25.3s], took_millis[2366], total_hits[3456], types[], stats[], search_type[QUERY_THEN_FETCH], total_shards[123], source[{"query":{"query_string":{"query":"*"}},"from":0,"size":"24","sort":{"updated_at":"desc"}}], id[],

The sample log above can be separated into the following fields, each of which will take its respective value from here and will then be uploaded to Site24x7.

Field name	Field value
DateTime	2022-09-18T02:19:14,861
LogLevel	WARN
Type	search
Phase	query
NodeId	tWO5cHxMRrGW3VuwRhIwYQ
NodeName	esd2C
Index	10772528_-1_-1_21_864
Shard	0
TimeTaken (ms)	2366
TotalHits	3456
Types
Stats
SearchType	QUERY_THEN_FETCH
TotalShared	123
Message	{"query":{"query_string":{"query":"*"}},"from":0,"size":"24","sort":{"updated_at":"desc"}}], id[],