Add gc_stat input plugin page

SUMMARY.md

@@ -87,6 +87,7 @@
   * [sample](input/sample.md)
   * [dummy](input/dummy.md)
   * [monitor\_agent](input/monitor_agent.md)
+  * [gc\_stat](input/gc_stat.md)
   * [windows\_eventlog](input/windows_eventlog.md)
 * [Output Plugins](output/README.md)
   * [file](output/file.md)

input/README.md

@@ -29,6 +29,9 @@ Input plugins extend Fluentd to retrieve and pull event logs from the external s
 * [`in_syslog`](syslog.md)
 * [`in_exec`](exec.md)
 * [`in_sample`](sample.md)
+* [`in_dummy`](dummy.md)
+* [`in_monitor_agent`](monitor_agent.md)
+* [`in_gc_stat`](gc_stat.md)
 * [`in_windows_eventlog`](windows_eventlog.md)
 
 ## Other Input Plugins

input/gc_stat.md

@@ -0,0 +1,90 @@
+# gc\_stat
+
+The `in_gc_stat` Input plugin periodically emits the statistics of the Ruby garbage collector of the running Fluentd process. Each record is the value returned by [`GC.stat`](https://docs.ruby-lang.org/en/master/GC.html#method-c-stat).
+
+It is included in Fluentd's core.
+
+{% hint style='danger' %}
+This plugin is a diagnostic tool to investigate a problem of Fluentd itself, such as a memory leak or an unexpected slowdown. Do not configure it in a production environment. Enable it only while you are collecting the data for a specific investigation, and remove it once the investigation is done.
+{% endhint %}
+
+## Example Configuration
+
+```text
+<source>
+  @type gc_stat
+  tag gc_stat
+  emit_interval 10
+</source>
+
+<match gc_stat>
+  @type stdout
+</match>
+```
+
+Refer to the [Configuration File](../configuration/config-file.md) article for the basic structure and syntax of the configuration file.
+
+## Plugin Helpers
+
+* [`timer`](../plugin-helper-overview/api-plugin-helper-timer.md)
+
+## Parameters
+
+See [Common Parameters](../configuration/plugin-common-parameters.md).
+
+### `@type` \(required\)
+
+The value must be `gc_stat`.
+
+### `tag` \(required\)
+
+| type | default | version |
+| :--- | :--- | :--- |
+| string | nil | 0.10.16 |
+
+The tag assigned to the emitted events.
+
+### `emit_interval`
+
+| type | default | version |
+| :--- | :--- | :--- |
+| time | 60 | 0.10.16 |
+
+The interval between the emits.
+
+### `use_symbol_keys`
+
+| type | default | version |
+| :--- | :--- | :--- |
+| bool | true | 1.11.0 |
+
+If `true`, the keys of the record are the symbols returned by `GC.stat`. If `false`, they are converted to strings.
+
+The default value assumes that the events are sent to [`out_stdout`](../output/stdout.md), which serializes the symbols as strings anyway. Set this parameter to `false` when you send the events to another plugin, because a plugin which looks up a field by its name expects string keys. For example, the [`csv`](../formatter/csv.md) formatter emits empty values for `fields count` unless `use_symbol_keys false` is set.
+
+## Output Example
+
+With the example configuration above, the events look like this:
+
+```text
+2026-08-24 10:38:04.387923158 +0900 gc_stat: {"count":20,"time":38,"marking_time":28,"sweeping_time":9,"heap_allocated_pages":184,"heap_empty_pages":0,"heap_allocatable_slots":0,"heap_available_slots":170033,"heap_live_slots":128266,"heap_free_slots":41767,"heap_final_slots":0,"heap_marked_slots":118143,"heap_eden_pages":184,"total_allocated_pages":184,"total_freed_pages":0,"total_allocated_objects":414773,"total_freed_objects":286507,"malloc_increase_bytes":1117672,"malloc_increase_bytes_limit":16777216,"minor_gc_count":15,"major_gc_count":5,"compact_count":0,"read_barrier_faults":0,"total_moved_objects":0,"remembered_wb_unprotected_objects":0,"remembered_wb_unprotected_objects_limit":676,"old_objects":116402,"old_objects_limit":135202,"oldmalloc_increase_bytes":3586192,"oldmalloc_increase_bytes_limit":16777216}
+```
+
+The set of the keys depends on the Ruby version which runs Fluentd. See [`GC.stat`](https://docs.ruby-lang.org/en/master/GC.html#method-c-stat) for the meaning of each key.
+
+## Multi-Process Environment
+
+If you use this plugin under the multi-process environment, each worker emits the statistics of its own process. Since the record itself has no field to tell the workers apart, embed `worker_id` in the tag:
+
+```text
+<source>
+  @type gc_stat
+  tag "gc_stat.#{worker_id}"
+</source>
+```
+
+See [config article](../configuration/config-file.md#embedded-ruby-code) for the embedded Ruby code.
+
+## Learn More
+
+* [Input Plugin Overview](./)