rkhachatryan commented on a change in pull request #18431:
URL: https://github.com/apache/flink/pull/18431#discussion_r791455950
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File path: docs/content/docs/ops/state/state_backends.md
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@@ -325,6 +325,126 @@ public class MyOptionsFactory implements
ConfigurableRocksDBOptionsFactory {
{{< top >}}
+## Enabling Changelog
+
+// todo: Chinese version of all changed docs
+
+// todo: mention in [large state tuning]({{< ref
"docs/ops/state/large_state_tuning" >}})? or 1.16?
+
+{{< hint warning >}} The feature is in experimental status. {{< /hint >}}
+
+{{< hint warning >}} Enabling Changelog may have a negative performance impact
on your application (see below). {{< /hint >}}
+
+### Introduction
+
+Changelog is a feature that aims to decrease checkpointing time, and therefore
end-to-end latency in exactly-once mode.
+
+Most commonly, checkpoint duration is affected by:
+
+1. Barrier travel time and alignment, addressed by
+ [Unaligned checkpoints]({{< ref
"docs/ops/state/checkpointing_under_backpressure#unaligned-checkpoints" >}})
+ and [Buffer debloating]({{< ref
"docs/ops/state/checkpointing_under_backpressure#buffer-debloating" >}})
+2. Snapshot creation time (so-called synchronous phase), addressed by
Asynchronous snapshots
Review comment:
> Snapshot creation time: (isn't that just preparing for changelogs to
be uploaded)?
> And previously snapshot creat time: flush + prepare SSTs to be uploaded?
Yes.
> Would these two parts significantly different?
> I think most of the time reduced is from the async phase
For changelog, it's usually under 100ms, without it can take tens of seconds
(above p99%). That can sound not much, but this phase blocks the entire
processing. I describe it
[here](https://github.com/apache/flink/pull/18431#discussion_r790436952).
But actually this statement is about reduction by using Async checkpoints
which were implemented long time ago, not related to the Changelog.
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