kowshik commented on a change in pull request #9001:
URL: https://github.com/apache/kafka/pull/9001#discussion_r498495464
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File path:
clients/src/main/java/org/apache/kafka/common/feature/SupportedVersionRange.java
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@@ -17,9 +17,16 @@
package org.apache.kafka.common.feature;
import java.util.Map;
+import java.util.Objects;
+import org.apache.kafka.common.utils.Utils;
/**
- * An extended {@link BaseVersionRange} representing the min/max versions for
supported features.
+ * An extended {@link BaseVersionRange} representing the min, max and first
active versions for a
+ * supported feature:
+ * - minVersion: This is the minimum supported version for the feature.
+ * - maxVersion: This the maximum supported version for the feature.
+ * - firstActiveVersion: This is the first active version for the feature.
Versions in the range
Review comment:
@junrao :
I'd like to discuss an example that cites a problem I'm concerned about.
> In general, we tend to deprecate a version very slowly in AK. So, if the
mistake is to deploy a new release that actually deprecates a supported
version. Old clients are likely all gone. So, moving finalized min version to
supported min version may not cause a big problem. We can just document that
people should make sure old versions are no longer used before deploying new
releases.
Let's say we have some feature `F` whose:
* Supported version range is: `[minVersion=1, maxVersion=6]`
* Existing finalized version range in the cluster is: `[minVersionLevel=1,
maxVersionLevel=6]`
Now, let us say a point in time arrives when we need to deprecate the
feature version `1`.
Let us say we bump up supported `minVersion` to `2` in a subsequent major
Kafka release.
Before this new release is deployed, let us assume the cluster operator
knows 100% that old clients that were using the feature at version `1` are
gone, so this is not a problem.
**PROBLEM:** Still, if we deploy this new release, the broker will consider
the following as a feature version incompatibility.
* Supported version range is: `[minVersion=2, maxVersion=6]`
* Existing finalized version range in the cluster is: `[minVersionLevel=1,
maxVersionLevel=6]`
Upon startup of a broker thats using the new release binary, the above
combination will crash the broker since supported `minVersion=2` is greater
than `minVersionLevel=1`. Basically the versioning system thinks that there is
now a broker that does not support `minVersionLevel=1`, which does not adhere
to the rules of the system.
Here is my thought: This is where `firstActiveVersion` becomes useful. By
bumping it up during a release (instead of the supported feature's
`minVersion`), we are able to get past this situation. When
`firstActiveVersion`is advanced in the code, and the cluster is deployed, the
controller (and all brokers) know that the advancement acts a request to the
controller to act upon the feature deprecation (by writing the advanced value
to the `FeatureZNode`). So, in this case we would release the broker with the
supported feature version range: `[minVersion=1, firstActiveVersion=2,
maxVersion=6]`, and the broker release wouldn't fail (because the intent is
clearly expressed to the versioning system).
What are your thoughts on the above?
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