[9.1] Add docs for ES|QL query logs (#131287)

docs/reference/query-languages/esql.md

@@ -20,4 +20,5 @@ This reference section provides detailed technical information about {{esql}} fe
 * [Advanced workflows](esql/esql-advanced.md): Learn how to handle more complex tasks with these guides, including how to extract, transform, and combine data from multiple indices
 * [Types and fields](esql/esql-types-and-fields.md): Learn about how {{esql}} handles different data types and special fields
 * [Limitations](esql/limitations.md): Learn about the current limitations of {{esql}}
-* [Examples](esql/esql-examples.md): Explore some example queries
+* [Examples](esql/esql-examples.md): Explore some example queries
+* [Troubleshooting](esql/esql-troubleshooting.md): Learn how to diagnose and resolve issues with {{esql}}

docs/reference/query-languages/esql/esql-query-log.md

@@ -0,0 +1,130 @@
+---
+navigation_title: "Query log"
+---
+
+# {{esql}} Query log [esql-query-log]
+
+
+The {{esql}} query log allows to log {{esql}} queries based on their execution time.
+
+You can use these logs to investigate, analyze or troubleshoot your cluster’s historical {{esql}} performance.
+
+{{esql}} query log reports task duration at coordinator level, but might not encompass the full task execution time observed on the client. For example, logs don’t surface HTTP network delays.
+
+Events that meet the specified threshold are emitted into  [{{es}} server logs](docs-content://deploy-manage/monitor/logging-configuration/update-elasticsearch-logging-levels.md).
+
+These logs can be found in local {{es}} service logs directory. Slow log files have a suffix of `_esql_querylog.json`.
+
+## Query log format [query-log-format]
+
+The following is an example of a successful query event in the query log:
+
+```js
+{
+    "@timestamp": "2025-03-11T08:39:50.076Z",
+    "log.level": "TRACE",
+    "auth.type": "REALM",
+    "elasticsearch.querylog.planning.took": 3108666,
+    "elasticsearch.querylog.planning.took_millis": 3,
+    "elasticsearch.querylog.query": "from index | limit 100",
+    "elasticsearch.querylog.search_type": "ESQL",
+    "elasticsearch.querylog.success": true,
+    "elasticsearch.querylog.took": 8050416,
+    "elasticsearch.querylog.took_millis": 8,
+    "user.name": "elastic-admin",
+    "user.realm": "default_file",
+    "ecs.version": "1.2.0",
+    "service.name": "ES_ECS",
+    "event.dataset": "elasticsearch.esql_querylog",
+    "process.thread.name": "elasticsearch[runTask-0][esql_worker][T#12]",
+    "log.logger": "esql.querylog.query",
+    "elasticsearch.cluster.uuid": "KZo1V7TcQM-O6fnqMm1t_g",
+    "elasticsearch.node.id": "uPgRE2TrSfa9IvnUpNT1Uw",
+    "elasticsearch.node.name": "runTask-0",
+    "elasticsearch.cluster.name": "runTask"
+}
+```
+
+The following is an example of a failing query event in the query log:
+
+```js
+{
+    "@timestamp": "2025-03-11T08:41:54.172Z",
+    "log.level": "TRACE",
+    "auth.type": "REALM",
+    "elasticsearch.querylog.error.message": "line 1:15: mismatched input 'limitxyz' expecting {DEV_CHANGE_POINT, 'enrich', 'dissect', 'eval', 'grok', 'limit', 'sort', 'stats', 'where', DEV_INLINESTATS, DEV_FORK, 'lookup', DEV_JOIN_LEFT, DEV_JOIN_RIGHT, DEV_LOOKUP, 'mv_expand', 'drop', 'keep', DEV_INSIST, 'rename'}",
+    "elasticsearch.querylog.error.type": "org.elasticsearch.xpack.esql.parser.ParsingException",
+    "elasticsearch.querylog.query": "from person | limitxyz 100",
+    "elasticsearch.querylog.search_type": "ESQL",
+    "elasticsearch.querylog.success": false,
+    "elasticsearch.querylog.took": 963750,
+    "elasticsearch.querylog.took_millis": 0,
+    "user.name": "elastic-admin",
+    "user.realm": "default_file",
+    "ecs.version": "1.2.0",
+    "service.name": "ES_ECS",
+    "event.dataset": "elasticsearch.esql_querylog",
+    "process.thread.name": "elasticsearch[runTask-0][search][T#16]",
+    "log.logger": "esql.querylog.query",
+    "elasticsearch.cluster.uuid": "KZo1V7TcQM-O6fnqMm1t_g",
+    "elasticsearch.node.id": "uPgRE2TrSfa9IvnUpNT1Uw",
+    "elasticsearch.node.name": "runTask-0",
+    "elasticsearch.cluster.name": "runTask"
+}
+```
+
+
+## Enable query logging [enable-query-log]
+
+You can enable query logging at cluster level.
+
+By default, all thresholds are set to `-1`, which results in no events being logged.
+
+Query log thresholds can be enabled for the four logging levels: `trace`, `debug`, `info`, and `warn`.
+
+To view the current query log settings, use the [get cluster settings API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-cluster-get-settings):
+
+```console
+GET _cluster/settings?filter_path=*.esql.querylog.*
+```
+
+You can use the `esql.querylog.include.user` setting to append `user.*` and `auth.type` fields to slow log entries. These fields contain information about the user who triggered the request.
+
+The following snippet adjusts all available {{esql}} query log settings [update cluster settings API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-cluster-put-settings):
+
+```console
+PUT /_cluster/settings
+{
+  "transient": {
+    "esql.querylog.threshold.warn": "10s",
+    "esql.querylog.threshold.info": "5s",
+    "esql.querylog.threshold.debug": "2s",
+    "esql.querylog.threshold.trace": "500ms",
+    "esql.querylog.include.user": true
+  }
+}
+```
+
+
+
+## Best practices for query logging [troubleshoot-query-log]
+
+Logging slow requests can be resource intensive to your {{es}} cluster depending on the qualifying traffic’s volume. For example, emitted logs might increase the index disk usage of your [{{es}} monitoring](docs-content://deploy-manage/monitor/stack-monitoring.md) cluster. To reduce the impact of slow logs, consider the following:
+
+* Set high thresholds to reduce the number of logged events.
+* Enable slow logs only when troubleshooting.
+
+If you aren’t sure how to start investigating traffic issues, consider enabling the `warn` threshold with a high `30s` threshold at the index level using the [update cluster settings API](https://www.elastic.co/docs/api/doc/elasticsearch/operation/operation-cluster-put-settings):
+
+Here is an example of how to change cluster settings to enable query logging at `warn` level, for queries taking more than 30 seconds, and include user information in the logs:
+
+```console
+PUT /_cluster/settings
+{
+  "transient": {
+    "esql.querylog.include.user": true,
+    "esql.querylog.threshold.warn": "30s"
+  }
+}
+```
+

docs/reference/query-languages/esql/esql-troubleshooting.md

@@ -0,0 +1,9 @@
+---
+navigation_title: "Troubleshooting"
+---
+
+# Troubleshooting {{esql}} [esql-troubleshooting]
+
+This section provides some useful resource for troubleshooting {{esql}}
+
+* [Query log](esql-query-log.md): Learn how to log {{esql}} queries

docs/reference/query-languages/toc.yml

@@ -119,6 +119,9 @@ toc:
 
       - file: esql/limitations.md
       - file: esql/esql-examples.md
+      - file: esql/esql-troubleshooting.md
+        children:
+          - file: esql/esql-query-log.md
   - file: sql.md
     children:
       - file: sql/sql-spec.md