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MINOR: improve the min.insync.replicas doc (#20237) 

Along with the change: https://github.com/apache/kafka/pull/17952

([KIP-966](https://cwiki.apache.org/confluence/display/KAFKA/KIP-966%3A+Eligible+Leader+Replicas)),
the semantics of `min.insync.replicas` config has small change, and add
some constraints. We should document them clearly.

Reviewers: Jun Rao <junrao@gmail.com>, Calvin Liu <caliu@confluent.io>,
 Mickael Maison <mickael.maison@gmail.com>, Paolo Patierno
 <ppatierno@live.com>, Federico Valeri <fedevaleri@gmail.com>, Chia-Ping
 Tsai <chia7712@gmail.com>
This commit is contained in:
Luke Chen 2025-08-05 00:22:13 +08:00 committed by Chia-Ping Tsai
parent 0179193b75
commit cdc7a4e2b7
4 changed files with 15 additions and 5 deletions
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3
clients/src/main/java/org/apache/kafka/common/config/TopicConfig.java
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@ -181,7 +181,8 @@ public class TopicConfig {
"When used together, <code>min.insync.replicas</code> and <code>acks</code> allow you to enforce greater durability guarantees. " +
"A typical scenario would be to create a topic with a replication factor of 3, " +
"set <code>min.insync.replicas</code> to 2, and produce with <code>acks</code> of \"all\". " +
"This will ensure that a majority of replicas must persist a write before it's considered successful by the producer and it's visible to consumers.";
"This ensures that a majority of replicas must persist a write before it's considered successful by the producer and it's visible to consumers." +
"<p>Note that when the Eligible Leader Replicas feature is enabled, the semantics of this config changes. Please refer to <a href=\"#eligible_leader_replicas\">the ELR section</a> for more info.</p>";
public static final String COMPRESSION_TYPE_CONFIG = "compression.type";
public static final String COMPRESSION_TYPE_DOC = "Specify the final compression type for a given topic. " +

13
docs/ops.html
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@ -4499,9 +4499,16 @@ $ bin/kafka-topics.sh --create --topic tieredTopic --bootstrap-server localhost:
<p>Downgrades are safe to perform by setting <code>eligible.leader.replicas.version=0</code>.</p>
<h4 class="anchor-heading"><a id="eligible_leader_replicas_tool" class="anchor-link"></a><a href="#eligible_leader_replicas_tool">Tool</a></h4>
<p>The ELR fields can be checked through the API DescribeTopicPartitions. The admin client can fetch the ELR info by describing the topics.
Also note that, if <code>min.insync.replicas</code> is updated for a topic, the ELR field will be cleaned. If cluster default min ISR is updated,
all the ELR fields will be cleaned.</p>
<p>The ELR fields can be checked through the API DescribeTopicPartitions. The admin client can fetch the ELR info by describing the topics.</p>
<p>Note that when the ELR feature is enabled:</p>
<ul>
<li>The cluster-level <code>min.insync.replicas</code> config will be added if there is not any. The value is the same as the static config in the active controller.</li>
<li>The removal of <code>min.insync.replicas</code> config at the cluster-level is not allowed.</li>
<li>If the cluster-level <code>min.insync.replicas</code> is updated, even if the value is unchanged, all the ELR state will be cleaned.</li>
<li>The previously set <code>min.insync.replicas</code> value at the broker-level config will be removed. Please set at the cluster-level if necessary.</li>
<li>The alteration of <code>min.insync.replicas</code> config at the broker-level is not allowed.</li>
<li>If <code>min.insync.replicas</code> is updated for a topic, the ELR state will be cleaned.</li>
</ul>
</script>

2
docs/upgrade.html
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@ -48,6 +48,8 @@
</li>
<li>
The KIP-966 part 1: Eligible Leader Replicas(ELR) will be enabled by default on the new clusters.
After the ELR feature enabled, the previously set <code>min.insync.replicas</code> value at the broker-level config will be removed.
Please set at the cluster-level if necessary.
For further details, please refer to <a href="/{{version}}/documentation.html#eligible_leader_replicas">here</a>.
</li>
</ul>

2
metadata/src/main/java/org/apache/kafka/controller/ConfigurationControlManager.java
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@ -613,7 +613,7 @@ public class ConfigurationControlManager {
/**
* Generate any configuration records that are needed to make it safe to enable ELR.
* Specifically, we need to remove all cluster-level configurations for min.insync.replicas,
* Specifically, we need to remove all broker-level configurations for min.insync.replicas,
* and create a cluster-level configuration for min.insync.replicas. It is always safe to call
* this function if ELR is already enabled; it will simply do nothing if the necessary
* configurations already exist.