Merge pull request ClickHouse#62015 from ClickHouse/docs-logger-json-…

…formatting

[Docs] Add info on JSON formatting for logger

docs/en/operations/server-configuration-parameters/settings.md

@@ -1354,6 +1354,7 @@ Keys:
 - `count` – The number of archived log files that ClickHouse stores.
 - `console` – Send `log` and `errorlog` to the console instead of file. To enable, set to `1` or `true`.
 - `stream_compress` – Compress `log` and `errorlog` with `lz4` stream compression. To enable, set to `1` or `true`.
+- `formatting` – Specify log format to be printed in console log (currently only `json` supported).
 
 Both log and error log file names (only file names, not directories) support date and time format specifiers.
 
@@ -1422,6 +1423,8 @@ Writing to the console can be configured. Config example:
 </logger>
 ```
 
+### syslog
+
 Writing to the syslog is also supported. Config example:
 
 ``` xml
@@ -1445,6 +1448,52 @@ Keys for syslog:
     Default value: `LOG_USER` if `address` is specified, `LOG_DAEMON` otherwise.
 - format – Message format. Possible values: `bsd` and `syslog.`
 
+### Log formats
+
+You can specify the log format that will be outputted in the console log. Currently, only JSON is supported. Here is an example of an output JSON log:
+
+```json
+{
+  "date_time": "1650918987.180175",
+  "thread_name": "#1",
+  "thread_id": "254545",
+  "level": "Trace",
+  "query_id": "",
+  "logger_name": "BaseDaemon",
+  "message": "Received signal 2",
+  "source_file": "../base/daemon/BaseDaemon.cpp; virtual void SignalListener::run()",
+  "source_line": "192"
+}
+```
+To enable JSON logging support, use the following snippet:
+
+```xml
+<logger>
+    <formatting>
+        <type>json</type>
+        <names>
+            <date_time>date_time</date_time>
+            <thread_name>thread_name</thread_name>
+            <thread_id>thread_id</thread_id>
+            <level>level</level>
+            <query_id>query_id</query_id>
+            <logger_name>logger_name</logger_name>
+            <message>message</message>
+            <source_file>source_file</source_file>
+            <source_line>source_line</source_line>
+        </names>
+    </formatting>
+</logger>
+```
+
+**Renaming keys for JSON logs**
+
+Key names can be modified by changing tag values inside the `<names>` tag. For example, to change `DATE_TIME` to `MY_DATE_TIME`, you can use `<date_time>MY_DATE_TIME</date_time>`.
+
+**Omitting keys for JSON logs**
+
+Log properties can be omitted by commenting out the property.  For example, if you do not want your log to print `query_id`, you can comment out the `<query_id>` tag.
+
 ## send_crash_reports {#send_crash_reports}
 
 Settings for opt-in sending crash reports to the ClickHouse core developers team via [Sentry](https://sentry.io).