Update 8.13.0 queue documentation and release notes (#983)

* Port output changes from Beats.

* Sync queue docs from Beats.

* Update docs/en/ingest-management/elastic-agent/configuration/outputs/output-logstash.asciidoc

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>

* Add backticks to other outputs.

---------

Co-authored-by: David Kilfoyle <41695641+kilfoyle@users.noreply.github.com>

docs/en/ingest-management/elastic-agent/configuration/outputs/output-elasticsearch.asciidoc

@@ -486,24 +486,34 @@ exports the API under a custom prefix.
 
 The memory queue keeps all events in memory.
 
-The memory queue waits for the output to acknowledge or drop events. If
-the queue is full, no new events can be inserted into the memory queue. Only
-after the signal from the output will the queue free up space for more events to be accepted.
-
-The memory queue is controlled by the parameters `queue.mem.flush.min_events` and `queue.mem.flush.timeout`. If
-`queue.mem.flush.timeout` is `0s` or `queue.mem.flush.min_events` is `0` or `1` then events can be sent by the output as
-soon as they are available. If the output supports a `bulk_max_size` parameter it controls the
-maximum batch size that can be sent.
-
-If `queue.mem.flush.min_events` is greater than `1` and `queue.mem.flush.timeout` is greater than `0s`, events will only
-be sent to the output when the queue contains at least `queue.mem.flush.min_events` events or the
-`queue.mem.flush.timeout` period has expired. In this mode the maximum size batch that that can be sent by the
-output is `queue.mem.flush.min_events`. If the output supports a `bulk_max_size` parameter, values of
-`bulk_max_size` greater than `queue.mem.flush.min_events` have no effect. The value of `queue.mem.flush.min_events`
-should be evenly divisible by `bulk_max_size` to avoid sending partial batches to the output.
-
-This sample configuration forwards events to the output if 512 events are available or the oldest
-available event has been waiting for 5s in the queue:
+The memory queue waits for the output to acknowledge or drop events. If the queue is full, no new
+events can be inserted into the memory queue. Only after the signal from the output will the queue
+free up space for more events to be accepted.
+
+The memory queue is controlled by the parameters `flush.min_events` and `flush.timeout`.
+`flush.min_events` gives a limit on the number of events that can be included in a single batch, and
+`flush.timeout` specifies how long the queue should wait to completely fill an event request. If the
+output supports a `bulk_max_size` parameter, the maximum batch size will be the smaller of
+`bulk_max_size` and `flush.min_events`.
+
+`flush.min_events` is a legacy parameter, and new configurations should prefer to control batch size
+with `bulk_max_size`. As of 8.13, there is never a performance advantage to limiting batch size with
+`flush.min_events` instead of `bulk_max_size`.
+
+In synchronous mode, an event request is always filled as soon as events are available, even if
+there are not enough events to fill the requested batch. This is useful when latency must be
+minimized. To use synchronous mode, set `flush.timeout` to 0.
+
+For backwards compatibility, synchronous mode can also be activated by setting `flush.min_events` to 0
+or 1. In this case, batch size will be capped at 1/2 the queue capacity.
+
+In asynchronous mode, an event request will wait up to the specified timeout to try and fill the
+requested batch completely. If the timeout expires, the queue returns a partial batch with all
+available events. To use asynchronous mode, set `flush.timeout` to a positive duration, for example 5s.
+
+This sample configuration forwards events to the output when there are enough events to fill the
+output's request (usually controlled by `bulk_max_size`, and limited to at most 512 events by
+`flush.min_events`), or when events have been waiting for
 
 [source,yaml]
 ------------------------------------------------------------------------------

docs/en/ingest-management/elastic-agent/configuration/outputs/output-kafka.asciidoc

@@ -148,24 +148,34 @@ output, {agent} can use SSL/TLS. For a list of available settings, refer to
 
 The memory queue keeps all events in memory.
 
-The memory queue waits for the output to acknowledge or drop events. If
-the queue is full, no new events can be inserted into the memory queue. Only
-after the signal from the output will the queue free up space for more events to be accepted.
-
-The memory queue is controlled by the parameters `queue.mem.flush.min_events` and `flush.timeout`. If
-`flush.timeout` is `0s` or `queue.mem.flush.min_events` is `0` or `1` then events can be sent by the output as
-soon as they are available. If the output supports a `bulk_max_size` parameter it controls the
-maximum batch size that can be sent.
-
-If `queue.mem.flush.min_events` is greater than `1` and `flush.timeout` is greater than `0s`, events will only
-be sent to the output when the queue contains at least `queue.mem.flush.min_events` events or the
-`flush.timeout` period has expired. In this mode the maximum size batch that that can be sent by the
-output is `queue.mem.flush.min_events`. If the output supports a `bulk_max_size` parameter, values of
-`bulk_max_size` greater than `queue.mem.flush.min_events` have no effect. The value of `queue.mem.flush.min_events`
-should be evenly divisible by `bulk_max_size` to avoid sending partial batches to the output.
-
-This sample configuration forwards events to the output if 512 events are available or the oldest
-available event has been waiting for 5s in the queue:
+The memory queue waits for the output to acknowledge or drop events. If the queue is full, no new
+events can be inserted into the memory queue. Only after the signal from the output will the queue
+free up space for more events to be accepted.
+
+The memory queue is controlled by the parameters `flush.min_events` and `flush.timeout`.
+`flush.min_events` gives a limit on the number of events that can be included in a single batch, and
+`flush.timeout` specifies how long the queue should wait to completely fill an event request. If the
+output supports a `bulk_max_size` parameter, the maximum batch size will be the smaller of
+`bulk_max_size` and `flush.min_events`.
+
+`flush.min_events` is a legacy parameter, and new configurations should prefer to control batch size
+with `bulk_max_size`. As of 8.13, there is never a performance advantage to limiting batch size with
+`flush.min_events` instead of `bulk_max_size`.
+
+In synchronous mode, an event request is always filled as soon as events are available, even if
+there are not enough events to fill the requested batch. This is useful when latency must be
+minimized. To use synchronous mode, set `flush.timeout` to 0.
+
+For backwards compatibility, synchronous mode can also be activated by setting `flush.min_events` to 0
+or 1. In this case, batch size will be capped at 1/2 the queue capacity.
+
+In asynchronous mode, an event request will wait up to the specified timeout to try and fill the
+requested batch completely. If the timeout expires, the queue returns a partial batch with all
+available events. To use asynchronous mode, set `flush.timeout` to a positive duration, for example 5s.
+
+This sample configuration forwards events to the output when there are enough events to fill the
+output's request (usually controlled by `bulk_max_size`, and limited to at most 512 events by
+`flush.min_events`), or when events have been waiting for
 
 [source,yaml]
 ------------------------------------------------------------------------------

docs/en/ingest-management/elastic-agent/configuration/outputs/output-logstash.asciidoc

@@ -169,23 +169,34 @@ For more information, refer to <<secure-logstash-connections>>.
 
 The memory queue keeps all events in memory.
 
-The memory queue waits for the output to acknowledge or drop events. If
-the queue is full, no new events can be inserted into the memory queue. Only
-after the signal from the output will the queue free up space for more events to be accepted.
-
-The memory queue is controlled by the parameters `queue.mem.flush.min_events` and `queue.mem.flush.timeout`. If
-`queue.mem.flush.timeout` is `0s` or `queue.mem.flush.min_events` is `0` or `1` then events can be sent by the output as
-soon as they are available. If the output supports a `bulk_max_size` parameter it controls the
-maximum batch size that can be sent.
-
-If `queue.mem.flush.min_events` is greater than `1` and `queue.mem.flush.timeout` is greater than `0s`, events will only
-be sent to the output when the queue contains at least `queue.mem.flush.min_events` events or the
-`queue.mem.flush.timeout` period has expired. In this mode the maximum size batch that that can be sent by the
-output is `queue.mem.flush.min_events`. If the output supports a `bulk_max_size` parameter, values of
-`bulk_max_size` greater than `queue.mem.flush.min_events` have no effect. The value of `queue.mem.flush.min_events`
-should be evenly divisible by `bulk_max_size` to avoid sending partial batches to the output.
-
-This sample configuration forwards events to the output if 512 events are available or the oldest
+The memory queue waits for the output to acknowledge or drop events. If the queue is full, no new
+events can be inserted into the memory queue. Only after the signal from the output will the queue
+free up space for more events to be accepted.
+
+The memory queue is controlled by the parameters `flush.min_events` and `flush.timeout`.
+`flush.min_events` gives a limit on the number of events that can be included in a single batch, and
+`flush.timeout` specifies how long the queue should wait to completely fill an event request. If the
+output supports a `bulk_max_size` parameter, the maximum batch size will be the smaller of
+`bulk_max_size` and `flush.min_events`.
+
+`flush.min_events` is a legacy parameter, and new configurations should prefer to control batch size
+with `bulk_max_size`. As of 8.13, there is never a performance advantage to limiting batch size with
+`flush.min_events` instead of `bulk_max_size`.
+
+In synchronous mode, an event request is always filled as soon as events are available, even if
+there are not enough events to fill the requested batch. This is useful when latency must be
+minimized. To use synchronous mode, set `flush.timeout` to 0.
+
+For backwards compatibility, synchronous mode can also be activated by setting `flush.min_events` to 0
+or 1. In this case, batch size will be capped at 1/2 the queue capacity.
+
+In asynchronous mode, an event request will wait up to the specified timeout to try and fill the
+requested batch completely. If the timeout expires, the queue returns a partial batch with all
+available events. To use asynchronous mode, set `flush.timeout` to a positive duration, for example 5s.
+
+This sample configuration forwards events to the output when there are enough events to fill the
+output's request (usually controlled by `bulk_max_size`, and limited to at most 512 events by
+`flush.min_events`), or when events have been waiting for 5s without filling the requested size:f 512 events are available or the oldest
 available event has been waiting for 5s in the queue:
 
 [source,yaml]

docs/en/ingest-management/elastic-agent/configuration/outputs/output-shared-settings.asciidoc

@@ -48,7 +48,7 @@ escaping.
 [id="{type}-queue.mem.events-setting"]
 `queue.mem.events`
 
-| The number of events the queue can store. This value should be evenly divisible by `queue.mem.flush.min_events` to avoid sending partial batches to the output.
+| The number of events the queue can store. This value should be evenly divisible by the smaller of `queue.mem.flush.min_events` or `bulk_max_size` to avoid sending partial batches to the output.
 
 *Default:* `3200 events`
 // end::queue.mem.events-setting[]
@@ -60,7 +60,7 @@ escaping.
 [id="{type}-queue.mem.flush.min_events-setting"]
 `queue.mem.flush.min_events`
 
-| The minimum number of events required for publishing. If this value is set to 0 or 1, events are available to the output immediately. If this value is greater than 1 the output must wait for the queue to accumulate this minimum number of events or for `queue.mem.flush.timeout` to expire before publishing. When greater than 1 this value also defines the maximum possible batch that can be sent by the output.
+| `flush.min_events` is a legacy parameter, and new configurations should prefer to control batch size with `bulk_max_size`. As of 8.13, there is never a performance advantage to limiting batch size with `flush.min_events` instead of `bulk_max_size`
 
 *Default:* `1600 events`
 // end::queue.mem.flush.min_events-setting[]

docs/en/ingest-management/release-notes/release-notes-8.13.asciidoc

@@ -66,6 +66,17 @@ Managed content relating to specific visualization editors such as Lens, TSVB, a
 For more information, refer to ({kibana-pull}172393[#172393]).
 ====
 
+// copied from Beats release notes: https://github.com/elastic/beats/pull/37795
+[discrete]
+[[breaking-37795]]
+.The behavior of `queue.mem.flush.min_events` has been simplified.
+[%collapsible]
+====
+*Details* +
+The behavior of `queue.mem.flush.min_events` has been simplified. It now serves as a simple maximum on the size of all event batches. There are no longer performance implications in its relationship to `bulk_max_size`.
+
+For more information, refer to ({beats-pull}37795[#37795]).
+====
 
 //[discrete]
 //[[known-issues-8.13.0]]
@@ -97,6 +108,7 @@ The 8.13.0 release added the following new and notable features.
 * Add a postrm script to {agent} DEB and RPM packages. {agent-pull}4334[#4334] {agent-issue}3784[#3784] {agent-issue}4267[#4267]
 * Kubernetes secrets provider has been improved to update a Kubernetes secret  when the secret value changes. {agent-pull}4371[#4371] {agent-issue}4168[#4168]
 * Upgrade link:https://github.com/elastic/elastic-agent-system-metrics[elastic-agent-system-metrics] to version 0.9.2. {agent-pull}4383[#4383]
+* Allow users to configure number of output workers (for outputs that support workers) with either `worker` or `workers`. {beats-pull}38257[38257]
 
 [discrete]
 [[enhancements-8.13.0]]