Apply suggestions from code review

Co-authored-by: Rob Bavey <[email protected]>

Author: yaauie

docs/reference/logstash-settings-file.md

@@ -68,7 +68,7 @@ The `logstash.yml` file includes these settings.
 | `queue.checkpoint.acks` | The maximum number of ACKed events before forcing a checkpoint when persistent queues are enabled (`queue.type: persisted`). Specify `queue.checkpoint.acks: 0` to set this value to unlimited. | 1024 |
 | `queue.checkpoint.writes` | The maximum number of written events before forcing a checkpoint when persistent queues are enabled (`queue.type: persisted`). Specify `queue.checkpoint.writes: 0` to set this value to unlimited. | 1024 |
 | `queue.checkpoint.retry` | When enabled, Logstash will retry four times per attempted checkpoint write for any checkpoint writes that fail. Any subsequent errors are not retried. This is a workaround for failed checkpoint writes that have been seen only on Windows platform, filesystems with non-standard behavior such as SANs and is not recommended except in those specific circumstances. (`queue.type: persisted`) | `true` |
-| `queue.compression` | Set a persisted queue compression level, which allows the pipeline to reduce the event size on disk at the cost of CPU usage. Possible values are `speed`, `balanced`, and `size`.  | `none` |
+| `queue.compression` {applies_to}`stack: ga 9.2` | Set a persisted queue compression level, which allows the pipeline to reduce the event size on disk at the cost of CPU usage. Possible values are `speed`, `balanced`, and `size`.  | `none` |
 | `queue.drain` | When enabled, Logstash waits until the persistent queue (`queue.type: persisted`) is drained before shutting down. | `false` |
 | `dead_letter_queue.enable` | Flag to instruct Logstash to enable the DLQ feature supported by plugins. | `false` |
 | `dead_letter_queue.max_bytes` | The maximum size of each dead letter queue. Entries will be dropped if they  would increase the size of the dead letter queue beyond this setting. | `1024mb` |

docs/reference/persistent-queues.md

@@ -86,11 +86,13 @@ If you want to define values for a specific pipeline, use [`pipelines.yml`](/ref
 
 `queue.compression` {applies_to}`stack: ga 9.2`
 :   Sets the event compression level for use with the Persisted Queue. Default is `none`. Possible values are:
+    * `none`: does not perform compression, but reads compressed events
     * `speed`: optimize for fastest compression operation
     * `size`: optimize for smallest possible size on disk, spending more CPU
     * `balanced`: a balance between the `speed` and `size` settings
 :::{important}
-Enabling compression will make the PQ incompatible with previous Logstash releases that did not support compression.
+Compression can be enabled for an existing PQ, but once compressed elements have been added to a PQ, that PQ cannot be read by previous Logstash releases that did not support compression.
+If you need to downgrade Logstash after enabling the PQ, you will need to either delete the PQ or run the pipeline with `queue.drain: true` first to ensure that no compressed elements remain.
 :::
 
 ## Configuration notes [pq-config-notes]