refactor(inkless): Rename diskless migration to diskless switch by giuseppelillo · Pull Request #601 · aiven/inkless

giuseppelillo · 2026-05-20T13:14:47Z

The term migration might be misleading as there's no data transfer involved in converting a classic topic to a diskless one. Use the term switch to be more evocative of what it really happens to all the partitions of the topic: each of them starts to append to the diskless log, and maintains what it was already present in the classic UnifiedLog.

giuseppelillo · 2026-05-20T13:16:45Z

-    public static final String DISKLESS_ALLOW_FROM_CLASSIC_ENABLE_DOC = "Allow migrating existing topics with remote.storage.enable=true from classic (diskless.enable=false) to diskless (diskless.enable=true). " +
-        "This should only be enabled in non-production environments for testing or migration purposes. " +
-        "When enabled, topics can have their diskless.enable config changed from false to true.";
+    public static final String DISKLESS_ALLOW_FROM_CLASSIC_ENABLE_DOC = "Allow switching existing topics from classic (diskless.enable=false) to diskless (diskless.enable=true). " +
+        "This should only be enabled in non-production environments for testing or switching purposes. " +
+        "When enabled, topics can have their diskless.enable config changed from false to true. " +
+        "Requires remote.log.storage.system.enable=true at the broker level.";


Removed the constraint on remote.storage.enable=true because also local-only classic topics can be switched to diskless.

Copilot

Pull request overview

This PR updates diskless classic→diskless terminology across the codebase, renaming “migration” to “switch” to better reflect that enabling diskless does not transfer existing data but changes where new data is appended.

Changes:

Renames classic→diskless “migration” APIs/constants to “switch” (controller flow, replica manager logic, pending state constant).
Updates log messages, config docs, and validation error messages to use “switch” terminology.
Updates/renames tests and metrics identifiers associated with init-diskless-log / switch flow.

Reviewed changes

Copilot reviewed 21 out of 21 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
storage/src/main/java/org/apache/kafka/storage/internals/log/LogConfig.java	Renames helper method + updates diskless/remote mutual-exclusion messaging to “switch”.
storage/inkless/src/main/java/io/aiven/inkless/control_plane/ControlPlane.java	Updates API Javadoc to “classic-to-diskless switch”.
server-common/src/main/java/org/apache/kafka/server/config/ServerConfigs.java	Updates broker config documentation for allow-from-classic using “switch” terminology.
metadata/src/test/java/org/apache/kafka/metadata/PartitionRegistrationTest.java	Updates tests to use renamed pending constant.
metadata/src/test/java/org/apache/kafka/controller/ReplicationControlManagerTest.java	Updates tests for renamed controller flow methods/constant.
metadata/src/main/java/org/apache/kafka/metadata/PartitionRegistration.java	Renames `CLASSIC_TO_DISKLESS_*_PENDING` constant to “SWITCH_PENDING”.
metadata/src/main/java/org/apache/kafka/controller/ReplicationControlManager.java	Renames method to `markClassicToDisklessSwitchStarted` and updates log message.
metadata/src/main/java/org/apache/kafka/controller/QuorumController.java	Updates call site to the renamed replication-control method.
core/src/test/scala/unit/kafka/server/ReplicaManagerTest.scala	Updates tests and mocks for renamed “switched” helpers and pending constant.
core/src/test/scala/unit/kafka/server/ReplicaFetcherThreadTest.scala	Renames eviction helper and updates field name assertions.
core/src/test/scala/unit/kafka/server/metadata/DisklessSwitchFlowTest.scala	Renames test class and updates metric name references for switch/init tracking.
core/src/test/scala/unit/kafka/server/InitDisklessLogManagerTest.scala	Updates tests to use renamed meters (completed/failed/retried).
core/src/test/scala/unit/kafka/server/DisklessFetchOffsetRouterTest.scala	Updates tests to use the renamed pending constant.
core/src/test/scala/unit/kafka/log/LogConfigTest.scala	Updates expected validation error strings to “switch”.
core/src/test/java/kafka/server/DisklessAndRemoteStorageConfigsTest.java	Updates expected validation error strings to “switch”.
core/src/main/scala/kafka/server/ReplicaManager.scala	Renames switch-related helpers and updates log messages/comments and pending-state routing.
core/src/main/scala/kafka/server/ReplicaFetcherThread.scala	Renames eviction buffer + eviction method and updates log message/comment.
core/src/main/scala/kafka/server/metadata/BrokerMetadataPublisher.scala	Updates call to renamed replica-manager sealing method.
core/src/main/scala/kafka/server/InitDisklessLogManager.scala	Renames metric identifiers and updates comments to “init diskless log” framing.
core/src/main/scala/kafka/server/DisklessFetchOffsetRouter.scala	Updates pending constant usage in routing logic.
core/src/main/scala/kafka/cluster/Partition.scala	Updates sealing/exception messages and comments to “diskless switch”.

Comments suppressed due to low confidence (2)

metadata/src/main/java/org/apache/kafka/controller/QuorumController.java:1938

migrationRecords now holds records returned by markClassicToDisklessSwitchStarted, so the name is inconsistent with the operation being performed. Renaming this local to something like switchRecords (or similar) will avoid confusion when reading alter-configs flow logic.

                List<ApiMessageAndVersion> migrationRecords =
                    replicationControl.markClassicToDisklessSwitchStarted(configChanges, result.response());
                if (!migrationRecords.isEmpty()) {
                    List<ApiMessageAndVersion> allRecords = BoundedList.newArrayBacked(MAX_RECORDS_PER_USER_OP);
                    allRecords.addAll(result.records());
                    allRecords.addAll(migrationRecords);

core/src/test/scala/unit/kafka/server/metadata/DisklessSwitchFlowTest.scala:153

Grammar in the updated comment reads awkwardly: “no init diskless log have completed/failed/retried yet.” Consider pluralizing to something like “no init diskless log operations have …” for clarity.

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Pull request overview

Copilot reviewed 22 out of 22 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

metadata/src/main/java/org/apache/kafka/controller/QuorumController.java:1938

The local variable name migrationRecords is now misleading after renaming the operation to “switch”. Please rename it (and related uses) to something like switchRecords to keep terminology consistent and avoid confusion during future maintenance.

                List<ApiMessageAndVersion> migrationRecords =
                    replicationControl.markClassicToDisklessSwitchStarted(configChanges, result.response());
                if (!migrationRecords.isEmpty()) {
                    List<ApiMessageAndVersion> allRecords = BoundedList.newArrayBacked(MAX_RECORDS_PER_USER_OP);
                    allRecords.addAll(result.records());
                    allRecords.addAll(migrationRecords);

jeqo

Thanks for looking into this! I added a couple of suggestions to simplify the metric naming, otherwise looks good to me.

jeqo

LGTM, thanks @giuseppelillo !

* refactor(inkless): Rename diskless migration to diskless switch The term migration might be misleading as there's no data transfer involved in converting a classic topic to a diskless one. Use the term switch to be more evocative of what it really happens to all the partitions of the topic: each of them starts to append to the diskless log, and maintains what it was already present in the classic UnifiedLog. * Fix suggestions * fix docs typo in diskless switch example * Fix metrics names

giuseppelillo commented May 20, 2026

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giuseppelillo requested a review from Copilot May 20, 2026 13:16

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Comment thread core/src/main/scala/kafka/server/DisklessFetchOffsetRouter.scala

Comment thread core/src/main/scala/kafka/server/ReplicaFetcherThread.scala Outdated

Comment thread core/src/main/scala/kafka/server/InitDisklessLogManager.scala Outdated

Fix suggestions

23c78ae

giuseppelillo force-pushed the giuseppelillo/rename-diskless-switch branch from 7be8ef2 to 23c78ae Compare May 20, 2026 13:36

giuseppelillo requested a review from Copilot May 20, 2026 13:43

Copilot started reviewing on behalf of giuseppelillo May 20, 2026 13:43 View session

Copilot AI reviewed May 20, 2026

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Comment thread docker/examples/docker-compose-files/inkless/README.md Outdated

Comment thread server-common/src/main/java/org/apache/kafka/server/config/ServerConfigs.java

Comment thread core/src/main/scala/kafka/server/InitDisklessLogManager.scala Outdated

giuseppelillo force-pushed the giuseppelillo/rename-diskless-switch branch from bd841fb to 17a898e Compare May 20, 2026 15:41

jeqo reviewed May 20, 2026

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giuseppelillo requested a review from jeqo May 20, 2026 16:57

jeqo approved these changes May 20, 2026

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giuseppelillo added 2 commits May 21, 2026 09:23

fix docs typo in diskless switch example

b17ee8d

Fix metrics names

3990aeb

giuseppelillo force-pushed the giuseppelillo/rename-diskless-switch branch from 0591cb6 to 3990aeb Compare May 21, 2026 07:24

giuseppelillo merged commit 49ecccf into main May 21, 2026
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giuseppelillo deleted the giuseppelillo/rename-diskless-switch branch May 21, 2026 07:24

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refactor(inkless): Rename diskless migration to diskless switch#601

refactor(inkless): Rename diskless migration to diskless switch#601
giuseppelillo merged 4 commits into
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