wombatu-kun commented on code in PR #13152: URL: https://github.com/apache/hudi/pull/13152#discussion_r3566195312
########## rfc/rfc-94/rfc-94.md: ########## @@ -0,0 +1,662 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +# RFC-94: Hudi Timeline User Interface (UI) + +## Proposers + +- @voonhous + +## Approvers + +- @danny0405 +- @rahil-c +- @yihua + +## Status + +JIRA: [HUDI-9315](https://issues.apache.org/jira/browse/HUDI-9315) + +## Abstract + +Hudi Timeline metadata is stored as timestamped files representing state transitions of actions like `commit`, +`deltacommit` and `compaction`. These files are accessible via the CLI or a file explorer, but it's hard to visualize +concurrent actions, spot missing transitions, or tell how long each step took. Debugging timeline issues by reading +filenames is tedious. + +This RFC proposes a UI-based timeline visualization tool that parses these metadata files, groups related actions, and +renders them in a time-ordered, interactive view. Users can track the lifecycle of each operation, see concurrency +patterns, and spot anomalies or long-running tasks. The implementation extends `hudi-timeline-service` with new `/v2/` +REST APIs and a static HTML + JavaScript frontend powered by [vis-timeline](https://github.com/visjs/vis-timeline), +served via Javalin's built-in static file serving with zero new Java compile-time dependencies. + +## Background + +Today, we rely on the CLI or direct filesystem inspection to understand timeline state through metadata files. These +files represent different actions (e.g., `deltacommit`, `compaction`) and their lifecycle states (`requested`, +`inflight`, `completed`), encoded in file names like: + +```shell +20250409102118815.deltacommit.inflight +20250409102118815.deltacommit.requested +20250409102118815_20250409102124339.deltacommit +20250409102121593.compaction.inflight +20250409102121593.compaction.requested +20250409102121593_20250409102122232.commit +20250409102124581.deltacommit.inflight +20250409102124581.deltacommit.requested +20250409102124581_20250409102125667.deltacommit +20250409102124612.compaction.inflight +20250409102124612.compaction.requested +20250409102124612_20250409102124892.commit +20250409102127348.deltacommit.inflight +20250409102127348.deltacommit.requested +20250409102127348_20250409102128481.deltacommit +20250409102127500.compaction.inflight +20250409102127500.compaction.requested +20250409102127500_20250409102127721.commit +``` + +This works, but has a few problems: + +1. No visibility into concurrency + - Multiple actions (e.g., `deltacommit` and `compaction`) often run concurrently. + - The CLI doesn't help correlate or visualize overlapping operations. +2. Lack of temporal context + - Timestamps are embedded in filenames but are hard to compare visually - year, month and day can be quickly + determined, but minutes and seconds are harder to parse. + - No easy way to tell how long an action took or whether it's stalling unless you manually calculate the difference + between requested and completion time. +3. Hard to spot inconsistencies or missing states + - An `inflight` compaction without a corresponding `commit` can indicate a starved/stuck compaction, which usually + blocks archiving/cleaning. + - These gaps are easy to miss when scanning filenames. + +On top of that, all timeline files are now stored as Avro binaries. Inspecting their contents requires custom Avro +readers to convert the binaries to JSON. + +## Scope + +This RFC covers visualization of metadata available in Hudi tables. All features are **READ-ONLY** - there is no support +for starting or spawning jobs that mutate a Hudi table. + +Alongside the timeline, the UI surfaces two additional read-only metadata views: the table's configuration +(`hoodie.properties`) and its schema-change history. + +The following are **out of scope**: + +- **Archived timeline:** Only the active timeline is rendered. Loading instants from LSM-based archive files is left for + future work. +- **Metadata table overlay:** The metadata table's own timeline is not shown alongside the main table timeline. +- **Write/mutation operations:** The UI cannot trigger compactions, clustering, or any write action. +- **Authentication/authorization:** No access control is added. The timeline server is assumed to run in a trusted + network, same as today. + + **Threat model:** The timeline and instant-detail views are `/v1`-parity - they read the same active-timeline and Review Comment: Neither view is `/v1`-parity after the switch to `metaClient.getActiveTimeline()`. The timeline view is now a superset: v1's `timeline/instants/all` is served from the `FileSystemView`'s write timeline, filtered to completed plus (log)compaction instants, while `/v2` reads the full active timeline and so additionally exposes `clean`, `rollback`, `savepoint`, `restore` and `indexing` instants and every requested/inflight state. The instant-detail view has no `/v1` counterpart at all: no route on `RemoteHoodieTableFileSystemView` returns instant content. `/v2/hoodie/view/timeline/instant` returns a deserialized `HoodieCommitMetadata`, which carries per-partition write stats and the table schema under the `schema` key of `extraMetadata`, the same schema exposure this paragraph counts as widening when it comes from the schema-history view. List both alongside table-config and schema-history rather than claiming parity for them. ########## rfc/rfc-94/rfc-94.md: ########## @@ -0,0 +1,662 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +# RFC-94: Hudi Timeline User Interface (UI) + +## Proposers + +- @voonhous + +## Approvers + +- @danny0405 +- @rahil-c +- @yihua + +## Status + +JIRA: [HUDI-9315](https://issues.apache.org/jira/browse/HUDI-9315) + +## Abstract + +Hudi Timeline metadata is stored as timestamped files representing state transitions of actions like `commit`, +`deltacommit` and `compaction`. These files are accessible via the CLI or a file explorer, but it's hard to visualize +concurrent actions, spot missing transitions, or tell how long each step took. Debugging timeline issues by reading +filenames is tedious. + +This RFC proposes a UI-based timeline visualization tool that parses these metadata files, groups related actions, and +renders them in a time-ordered, interactive view. Users can track the lifecycle of each operation, see concurrency +patterns, and spot anomalies or long-running tasks. The implementation extends `hudi-timeline-service` with new `/v2/` +REST APIs and a static HTML + JavaScript frontend powered by [vis-timeline](https://github.com/visjs/vis-timeline), +served via Javalin's built-in static file serving with zero new Java compile-time dependencies. + +## Background + +Today, we rely on the CLI or direct filesystem inspection to understand timeline state through metadata files. These +files represent different actions (e.g., `deltacommit`, `compaction`) and their lifecycle states (`requested`, +`inflight`, `completed`), encoded in file names like: + +```shell +20250409102118815.deltacommit.inflight +20250409102118815.deltacommit.requested +20250409102118815_20250409102124339.deltacommit +20250409102121593.compaction.inflight +20250409102121593.compaction.requested +20250409102121593_20250409102122232.commit +20250409102124581.deltacommit.inflight +20250409102124581.deltacommit.requested +20250409102124581_20250409102125667.deltacommit +20250409102124612.compaction.inflight +20250409102124612.compaction.requested +20250409102124612_20250409102124892.commit +20250409102127348.deltacommit.inflight +20250409102127348.deltacommit.requested +20250409102127348_20250409102128481.deltacommit +20250409102127500.compaction.inflight +20250409102127500.compaction.requested +20250409102127500_20250409102127721.commit +``` + +This works, but has a few problems: + +1. No visibility into concurrency + - Multiple actions (e.g., `deltacommit` and `compaction`) often run concurrently. + - The CLI doesn't help correlate or visualize overlapping operations. +2. Lack of temporal context + - Timestamps are embedded in filenames but are hard to compare visually - year, month and day can be quickly + determined, but minutes and seconds are harder to parse. + - No easy way to tell how long an action took or whether it's stalling unless you manually calculate the difference + between requested and completion time. +3. Hard to spot inconsistencies or missing states + - An `inflight` compaction without a corresponding `commit` can indicate a starved/stuck compaction, which usually + blocks archiving/cleaning. + - These gaps are easy to miss when scanning filenames. + +On top of that, all timeline files are now stored as Avro binaries. Inspecting their contents requires custom Avro +readers to convert the binaries to JSON. + +## Scope + +This RFC covers visualization of metadata available in Hudi tables. All features are **READ-ONLY** - there is no support +for starting or spawning jobs that mutate a Hudi table. + +Alongside the timeline, the UI surfaces two additional read-only metadata views: the table's configuration +(`hoodie.properties`) and its schema-change history. + +The following are **out of scope**: + +- **Archived timeline:** Only the active timeline is rendered. Loading instants from LSM-based archive files is left for + future work. +- **Metadata table overlay:** The metadata table's own timeline is not shown alongside the main table timeline. +- **Write/mutation operations:** The UI cannot trigger compactions, clustering, or any write action. +- **Authentication/authorization:** No access control is added. The timeline server is assumed to run in a trusted + network, same as today. + + **Threat model:** The timeline and instant-detail views are `/v1`-parity - they read the same active-timeline and + filesystem metadata the existing `/v1/` REST APIs already serve, on the same network interface (the server binds to + all interfaces on the driver/standalone host). Two views widen the read surface beyond `/v1`, whose routes serve only + file-slice/base-file/timeline DTOs: the table-config view (`/v2/hoodie/view/table/config`) returns the full + `hoodie.properties` via `HoodieTableConfig.getProps()`, and the schema-history view + (`/v2/hoodie/view/table/schema/history`) exposes current and historical table schemas. Table properties can reference + sensitive material - KMS endpoints, lock-provider connection strings, external key/vault paths - though they rarely + embed secrets directly. The first cut serves table config unfiltered (sorted, as-is); the same content is already + readable by anyone with filesystem access to `.hoodie/hoodie.properties`. The primary control is that all UI routes, + including these two, are gated behind `--enable-ui` (off by default), with the server assumed to run on a trusted + network; a redacting/allowlisted config view is a possible future refinement for less-trusted interfaces. The UI adds + no write or mutation capability. Operators on untrusted networks should front the server with a reverse proxy or + restrict it to a private interface / localhost via network policy. + +## Implementation + +Keeping the implementation lightweight is a priority - we should add as few dependencies as possible. Changes go into +the existing `hudi-timeline-service` module, which contains a Javalin web-application that caches filesystem metadata of +a Hudi table for job executors during tagging/writing. + +The first cut runs the UI on the Timeline Server in **STANDALONE** mode (see [Configuration](#configuration)) and is +self-contained within `hudi-timeline-service`. Enabling the UI on the **EMBEDDED** timeline server inside a Spark +driver, together with a Spark UI tab, requires cross-module wiring (`hudi-client-common`, `hudi-spark-client`); it is +designed below but deferred to a follow-up to keep the initial PR small and focused. The standalone UI lands first; the +embedded/Spark linking lands next. + +The Hudi Timeline UI has two parts: the frontend and backend. + +### Architecture + +The timeline server can run standalone or embedded inside a Spark driver. In embedded mode, a tab in the Spark UI links +directly to the Hudi Timeline UI. The embedded mode and Spark UI tab (right side of the diagram below) are a planned +follow-up; the first cut is standalone-only. + +```mermaid +graph LR + Browser["Browser"] + + subgraph Driver["Standalone / Spark Driver"] + subgraph TimelineServer["Javalin (Timeline Server)"] + Static["/ui entry + /ui/static/*\n(HTML, JS, CSS)"] + API["/v2/hoodie/view/* - TimelineHandler"] + Meta["HoodieTableMetaClient\n(active timeline, config, schema)"] + + API --> Meta + end + + subgraph SparkUI["Spark UI (:4040) - embedded mode (follow-up)"] + direction TB + SparkUIPad[ ] ~~~ Tabs["[Jobs] [Stages] ... [Hudi Timeline]"] + end + + style SparkUIPad fill:none,stroke:none,color:none + + Tabs -- "link" --> Static + end + + Browser -- "HTTP" --> Static + Browser -- "HTTP" --> API + Browser -. "HTTP\n(embedded mode)" .-> SparkUI +``` + +There are two categories of requests: + +1. **Static file requests** - Javalin serves JavaScript, CSS, and library assets from the classpath + (`src/main/resources/public/`) under the `/ui/static/` URL prefix; `UiHandler` serves `index.html` at `/ui`. No + server-side rendering or template engine is needed. +2. **REST API requests** (`/v2/hoodie/view/*`) - `TimelineHandler` processes these requests, reading from a short-lived + `HoodieTableMetaClient` built for the request's basepath - its `getActiveTimeline()` for the timeline routes, and + table config/schema for the config/schema routes - and returning JSON. + +### Frontend + +The frontend is static HTML pages with vanilla JavaScript, similar to the Spark Web UI. Javalin's built-in static file +serving handles files from the classpath - no template engine (e.g., Thymeleaf) is needed and no new Java compile-time +dependencies are added. + +No frontend build pipeline (npm, webpack, vite) is needed. Contributing to the UI requires only a text editor. Three +libraries are vendored as static assets: vis-timeline (timeline rendering), Bootstrap 5 (layout/styling), and renderjson +(collapsible JSON in the detail panel). + +#### File Structure + +``` +hudi-timeline-service/src/main/resources/public/ +├── index.html # Landing page with basepath input form +├── js/ +│ └── timeline.js # vis-timeline initialization and REST API calls +├── css/ +│ └── style.css # Basic styling +└── lib/ # Vendored third-party assets (see Dependency Impact) + ├── vis-timeline/ # Timeline rendering (Apache-2.0 OR MIT) + │ ├── vis-timeline-graph2d.min.js + │ └── vis-timeline-graph2d.min.css + ├── bootstrap/ # Layout/styling (MIT) + │ ├── bootstrap.bundle.min.js + │ └── bootstrap.min.css + └── renderjson/ # Collapsible JSON detail panel (ISC) + └── renderjson.js +``` + +#### JavaScript Delivery: Bundled, No External Calls + +All three libraries are served from bundled copies under `/ui/static/lib/` (`/ui/static/lib/vis-timeline/`, +`/ui/static/lib/bootstrap/`, `/ui/static/lib/renderjson/`). The UI makes no external network calls, so it works out of +the box in air-gapped and security-conscious deployments with no extra configuration. The bundled, minified assets add +~890KB to the JAR (vis-timeline ~575KB, Bootstrap 5 ~305KB, renderjson ~11KB). + +Pinning a vendored copy (rather than loading from a CDN) keeps the UI deterministic and avoids a runtime dependency on +an external host being reachable. If automatic patch updates are wanted later, a CDN source can be added as an opt-in +config flag without changing this default. + +#### vis-timeline Configuration + +The timeline is configured with groups and items that map to Hudi's timeline model: + +- **Groups:** One row per action type - `commit`, `deltacommit`, `compaction`, `clean`, `rollback`, `clustering`, + `savepoint`, `logcompaction`, `indexing`, `restore`, `replacecommit`. These correspond to the actions in Review Comment: The active timeline collapses states before the handler sees them. `HoodieTableMetaClient.getActiveTimeline()` builds an `ActiveTimelineV2` with `applyLayoutFilter` true, which runs `TimelineLayout.filterHoodieInstantsByLatestState`: instants are grouped by `(requestedTime, getComparableAction(action))` and only the highest state survives. `InstantComparatorV2.COMPARABLE_ACTIONS` maps `compaction` to `commit`, `logcompaction` to `deltacommit`, and `clustering` to `replacecommit`. So a completed compaction reaches `getTimelineV2` as a single instant whose action is `commit`, since its completed file is `.commit`. The `compaction`, `logcompaction` and `clustering` rows can then only ever hold pending point items, and a completed compaction renders as a range bar in the `commit` row, indistinguishable from an ordinary commit. That undercuts the stuck-compaction diagnosis this RFC opens with, and it also makes the Test Plan's "all action types in `VALID_ACTIONS_IN_TIMELINE` are mapped correctly" unsatisfiable as written. Specify how the UI recovers the originating action, for example by carrying the pending instant's action on `InstantDTOV2`, or by grouping on the requested/inflight file rather than on the surviving instant. ########## rfc/rfc-94/rfc-94.md: ########## @@ -0,0 +1,662 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +# RFC-94: Hudi Timeline User Interface (UI) + +## Proposers + +- @voonhous + +## Approvers + +- @danny0405 +- @rahil-c +- @yihua + +## Status + +JIRA: [HUDI-9315](https://issues.apache.org/jira/browse/HUDI-9315) + +## Abstract + +Hudi Timeline metadata is stored as timestamped files representing state transitions of actions like `commit`, +`deltacommit` and `compaction`. These files are accessible via the CLI or a file explorer, but it's hard to visualize +concurrent actions, spot missing transitions, or tell how long each step took. Debugging timeline issues by reading +filenames is tedious. + +This RFC proposes a UI-based timeline visualization tool that parses these metadata files, groups related actions, and +renders them in a time-ordered, interactive view. Users can track the lifecycle of each operation, see concurrency +patterns, and spot anomalies or long-running tasks. The implementation extends `hudi-timeline-service` with new `/v2/` +REST APIs and a static HTML + JavaScript frontend powered by [vis-timeline](https://github.com/visjs/vis-timeline), +served via Javalin's built-in static file serving with zero new Java compile-time dependencies. + +## Background + +Today, we rely on the CLI or direct filesystem inspection to understand timeline state through metadata files. These +files represent different actions (e.g., `deltacommit`, `compaction`) and their lifecycle states (`requested`, +`inflight`, `completed`), encoded in file names like: + +```shell +20250409102118815.deltacommit.inflight +20250409102118815.deltacommit.requested +20250409102118815_20250409102124339.deltacommit +20250409102121593.compaction.inflight +20250409102121593.compaction.requested +20250409102121593_20250409102122232.commit +20250409102124581.deltacommit.inflight +20250409102124581.deltacommit.requested +20250409102124581_20250409102125667.deltacommit +20250409102124612.compaction.inflight +20250409102124612.compaction.requested +20250409102124612_20250409102124892.commit +20250409102127348.deltacommit.inflight +20250409102127348.deltacommit.requested +20250409102127348_20250409102128481.deltacommit +20250409102127500.compaction.inflight +20250409102127500.compaction.requested +20250409102127500_20250409102127721.commit +``` + +This works, but has a few problems: + +1. No visibility into concurrency + - Multiple actions (e.g., `deltacommit` and `compaction`) often run concurrently. + - The CLI doesn't help correlate or visualize overlapping operations. +2. Lack of temporal context + - Timestamps are embedded in filenames but are hard to compare visually - year, month and day can be quickly + determined, but minutes and seconds are harder to parse. + - No easy way to tell how long an action took or whether it's stalling unless you manually calculate the difference + between requested and completion time. +3. Hard to spot inconsistencies or missing states + - An `inflight` compaction without a corresponding `commit` can indicate a starved/stuck compaction, which usually + blocks archiving/cleaning. + - These gaps are easy to miss when scanning filenames. + +On top of that, all timeline files are now stored as Avro binaries. Inspecting their contents requires custom Avro +readers to convert the binaries to JSON. + +## Scope + +This RFC covers visualization of metadata available in Hudi tables. All features are **READ-ONLY** - there is no support +for starting or spawning jobs that mutate a Hudi table. + +Alongside the timeline, the UI surfaces two additional read-only metadata views: the table's configuration +(`hoodie.properties`) and its schema-change history. + +The following are **out of scope**: + +- **Archived timeline:** Only the active timeline is rendered. Loading instants from LSM-based archive files is left for + future work. +- **Metadata table overlay:** The metadata table's own timeline is not shown alongside the main table timeline. +- **Write/mutation operations:** The UI cannot trigger compactions, clustering, or any write action. +- **Authentication/authorization:** No access control is added. The timeline server is assumed to run in a trusted + network, same as today. + + **Threat model:** The timeline and instant-detail views are `/v1`-parity - they read the same active-timeline and + filesystem metadata the existing `/v1/` REST APIs already serve, on the same network interface (the server binds to + all interfaces on the driver/standalone host). Two views widen the read surface beyond `/v1`, whose routes serve only + file-slice/base-file/timeline DTOs: the table-config view (`/v2/hoodie/view/table/config`) returns the full + `hoodie.properties` via `HoodieTableConfig.getProps()`, and the schema-history view + (`/v2/hoodie/view/table/schema/history`) exposes current and historical table schemas. Table properties can reference + sensitive material - KMS endpoints, lock-provider connection strings, external key/vault paths - though they rarely + embed secrets directly. The first cut serves table config unfiltered (sorted, as-is); the same content is already + readable by anyone with filesystem access to `.hoodie/hoodie.properties`. The primary control is that all UI routes, + including these two, are gated behind `--enable-ui` (off by default), with the server assumed to run on a trusted + network; a redacting/allowlisted config view is a possible future refinement for less-trusted interfaces. The UI adds + no write or mutation capability. Operators on untrusted networks should front the server with a reverse proxy or + restrict it to a private interface / localhost via network policy. + +## Implementation + +Keeping the implementation lightweight is a priority - we should add as few dependencies as possible. Changes go into +the existing `hudi-timeline-service` module, which contains a Javalin web-application that caches filesystem metadata of +a Hudi table for job executors during tagging/writing. + +The first cut runs the UI on the Timeline Server in **STANDALONE** mode (see [Configuration](#configuration)) and is +self-contained within `hudi-timeline-service`. Enabling the UI on the **EMBEDDED** timeline server inside a Spark +driver, together with a Spark UI tab, requires cross-module wiring (`hudi-client-common`, `hudi-spark-client`); it is +designed below but deferred to a follow-up to keep the initial PR small and focused. The standalone UI lands first; the +embedded/Spark linking lands next. + +The Hudi Timeline UI has two parts: the frontend and backend. + +### Architecture + +The timeline server can run standalone or embedded inside a Spark driver. In embedded mode, a tab in the Spark UI links +directly to the Hudi Timeline UI. The embedded mode and Spark UI tab (right side of the diagram below) are a planned +follow-up; the first cut is standalone-only. + +```mermaid +graph LR + Browser["Browser"] + + subgraph Driver["Standalone / Spark Driver"] + subgraph TimelineServer["Javalin (Timeline Server)"] + Static["/ui entry + /ui/static/*\n(HTML, JS, CSS)"] + API["/v2/hoodie/view/* - TimelineHandler"] + Meta["HoodieTableMetaClient\n(active timeline, config, schema)"] + + API --> Meta + end + + subgraph SparkUI["Spark UI (:4040) - embedded mode (follow-up)"] + direction TB + SparkUIPad[ ] ~~~ Tabs["[Jobs] [Stages] ... [Hudi Timeline]"] + end + + style SparkUIPad fill:none,stroke:none,color:none + + Tabs -- "link" --> Static + end + + Browser -- "HTTP" --> Static + Browser -- "HTTP" --> API + Browser -. "HTTP\n(embedded mode)" .-> SparkUI +``` + +There are two categories of requests: + +1. **Static file requests** - Javalin serves JavaScript, CSS, and library assets from the classpath + (`src/main/resources/public/`) under the `/ui/static/` URL prefix; `UiHandler` serves `index.html` at `/ui`. No + server-side rendering or template engine is needed. +2. **REST API requests** (`/v2/hoodie/view/*`) - `TimelineHandler` processes these requests, reading from a short-lived + `HoodieTableMetaClient` built for the request's basepath - its `getActiveTimeline()` for the timeline routes, and + table config/schema for the config/schema routes - and returning JSON. + +### Frontend + +The frontend is static HTML pages with vanilla JavaScript, similar to the Spark Web UI. Javalin's built-in static file +serving handles files from the classpath - no template engine (e.g., Thymeleaf) is needed and no new Java compile-time +dependencies are added. + +No frontend build pipeline (npm, webpack, vite) is needed. Contributing to the UI requires only a text editor. Three +libraries are vendored as static assets: vis-timeline (timeline rendering), Bootstrap 5 (layout/styling), and renderjson +(collapsible JSON in the detail panel). + +#### File Structure + +``` +hudi-timeline-service/src/main/resources/public/ +├── index.html # Landing page with basepath input form +├── js/ +│ └── timeline.js # vis-timeline initialization and REST API calls +├── css/ +│ └── style.css # Basic styling +└── lib/ # Vendored third-party assets (see Dependency Impact) + ├── vis-timeline/ # Timeline rendering (Apache-2.0 OR MIT) + │ ├── vis-timeline-graph2d.min.js + │ └── vis-timeline-graph2d.min.css + ├── bootstrap/ # Layout/styling (MIT) + │ ├── bootstrap.bundle.min.js + │ └── bootstrap.min.css + └── renderjson/ # Collapsible JSON detail panel (ISC) + └── renderjson.js +``` + +#### JavaScript Delivery: Bundled, No External Calls + +All three libraries are served from bundled copies under `/ui/static/lib/` (`/ui/static/lib/vis-timeline/`, +`/ui/static/lib/bootstrap/`, `/ui/static/lib/renderjson/`). The UI makes no external network calls, so it works out of +the box in air-gapped and security-conscious deployments with no extra configuration. The bundled, minified assets add +~890KB to the JAR (vis-timeline ~575KB, Bootstrap 5 ~305KB, renderjson ~11KB). + +Pinning a vendored copy (rather than loading from a CDN) keeps the UI deterministic and avoids a runtime dependency on +an external host being reachable. If automatic patch updates are wanted later, a CDN source can be added as an opt-in +config flag without changing this default. + +#### vis-timeline Configuration + +The timeline is configured with groups and items that map to Hudi's timeline model: + +- **Groups:** One row per action type - `commit`, `deltacommit`, `compaction`, `clean`, `rollback`, `clustering`, + `savepoint`, `logcompaction`, `indexing`, `restore`, `replacecommit`. These correspond to the actions in + `HoodieTimeline.VALID_ACTIONS_IN_TIMELINE`. +- **Items:** Completed instants are rendered as range bars spanning from `requestedTime` to `completionTime`. + Non-completed instants (requested or inflight) are rendered as point items at `requestedTime`. +- **Color coding:** Items are colored by state: + - Green -> `COMPLETED` + - Yellow -> `INFLIGHT` + - Red -> `REQUESTED` +- **Tooltip:** On hover, shows the action type, requested time, completion time, and duration. +- **Click handler:** Clicking an instant fetches its detail via `/v2/hoodie/view/timeline/instant` and shows the + deserialized JSON in a detail panel below the timeline. + +### Backend + +A `hudi-timeline-service` instance already serves filesystem metadata for multiple table basePaths since the +`FileSystemView`s are cached in a map keyed by basepath. + +We extend this module with `/v2/` APIs that serve the UI's timeline, config and schema metadata, reading each table +through a short-lived `HoodieTableMetaClient` built per request (see [Handler Design](#handler-design)). + +#### API Specification + +| Method | Path | Parameters | Response | Description | +|--------|-----------------------------------------|-----------------------------------------------------------------------|-----------------|----------------------------------------------------------------------------------------------| +| GET | `/v2/hoodie/view/timeline/instants/all` | `basepath` (required) | `TimelineDTOV2` | All active instants (each with requested time, completion time, action, state), wrapped in a timeline DTO | +| GET | `/v2/hoodie/view/timeline/instant` | `basepath`, `instant`, `instantaction`, `instantstate` (all required) | JSON string | Deserialized content of a specific instant's metadata (Avro -> JSON) | +| GET | `/v2/hoodie/view/table/config` | `basepath` (required) | JSON object | The table's `hoodie.properties` (sorted) | +| GET | `/v2/hoodie/view/table/schema/history` | `basepath` (required), `limit` (optional, default 200, max 1000) | JSON object | Current schema, per-commit schema-change history from the last `limit` commits, and `.schema` internal-schema history when present | + +Static assets (JS, CSS, library files) are served from the classpath directory `src/main/resources/public/`, mounted +under the `/ui/static/` URL prefix via Javalin's static-files `hostedPath` (e.g., `/ui/static/js/timeline.js`, +`/ui/static/lib/...`). Namespacing everything UI under `/ui` keeps the UI surface from colliding with `/v1/`, `/v2/`, or +any future module-registered routes on the same Javalin instance, rather than reserving root prefixes like `/js`, +`/css`, and `/lib`. `UiHandler` additionally registers `GET /ui`, which returns `index.html` (with asset links pointing +at `/ui/static/...`) to give the UI a stable entry URL. + +**On response size and pagination:** `GET /v2/hoodie/view/timeline/instants/all` returns the full active timeline. The +active timeline is bounded by archiving (the unbounded archived timeline is out of scope), so instant counts are +typically modest. The first cut intentionally returns all active instants and relies on client-side zoom/scroll and +filtering for navigation. If active-timeline sizes become a concern, the endpoint can be extended additively with +optional `from`/`to` time-range query params (and/or a `limit`) without breaking the existing contract. + +#### DTO Design + +The UI's timeline endpoint returns a `TimelineDTOV2` built from two v2 DTOs in a `v2` package, leaving the existing +`/v1/` API contract untouched. + +The v1 `InstantDTO` already carries everything needed to render range bars - `fromInstant` populates both +`requestedTime` and `completionTime` from `HoodieInstant` (added under HUDI-9332) - so the UI could consume the v1 +timeline DTO directly. The v2 DTOs are not about exposing new fields; they are a deliberate, low-cost choice to give the +new `/v2/` API a cleaner JSON contract: + +- **`InstantDTOV2`** (`o.a.h.common.table.timeline.dto.v2`) - the same source fields as v1, with UI-oriented JSON keys: + - `action` - the action type (e.g., `commit`, `deltacommit`, `compaction`) + - `requestedTime` (JSON `requestTs`) - requested timestamp (`HoodieInstant.requestedTime()`) + - `completionTime` (JSON `completionTs`) - completion timestamp (`HoodieInstant.getCompletionTime()`), null for + non-completed instants + - `state` - the instant state (`REQUESTED`, `INFLIGHT`, `COMPLETED`) + + Versus v1, this renames `requestedTime`/`completionTime` to `requestTs`/`completionTs` and drops v1's redundant legacy + `ts` field (a duplicate of the requested time that the UI does not need). +- **`TimelineDTOV2`** - wraps a `List<InstantDTOV2>` (`instants`); this is what `/v2/hoodie/view/timeline/instants/all` + returns. + + Both v2 DTOs carry the `V2` suffix to mirror the repo's versioned-class convention (`versioning/v1`/`v2` with + `InstantGeneratorV1`/`V2`, `BaseTimelineV1`/`V2`) and to avoid a simple-name clash with the existing `dto.InstantDTO` + that `TimelineHandler` still imports for the v1 routes. + +#### Handler Design + +The v2 endpoints are served by the existing `TimelineHandler` (which already serves the v1 timeline routes); a separate +`UiHandler` serves only the UI entry page. + +`TimelineHandler` methods: + +1. `getTimelineV2(basePath)` - maps `getActiveTimeline()` from the request's `HoodieTableMetaClient` to a + `TimelineDTOV2`. The active timeline carries every `VALID_ACTIONS_IN_TIMELINE` action in all states + (requested/inflight/completed), which the vis-timeline groups and requested/inflight point items require. The + `FileSystemView` timeline (`getFileSystemView(basePath).getTimeline()`) cannot be used here: it is the write timeline + filtered to completed plus (log)compaction instants, so it drops `clean`/`rollback`/`savepoint`/`restore`/`indexing` + and every requested/inflight state. +2. `getInstantDetails(basePath, instant, action, state)` - reads the instant's Avro content via the active timeline's + `getContentStream(instant)` (the non-deprecated reader method; `getInstantDetails()` is `@Deprecated`) and + deserializes it to JSON. The instant is built with the request's metaClient via `metaClient.getInstantGenerator()`; + a malformed `state`/`action` returns 400, a read failure is logged and returns 500. +3. `getTableConfig(basePath)` - returns the table's `hoodie.properties` as a sorted JSON object. +4. `getSchemaHistory(basePath, limit)` - reconstructs schema evolution from two sources; see + [Schema-History Reconstruction](#schema-history-reconstruction) below. + +`getTimelineV2`, `getTableConfig` and `getSchemaHistory` each build a short-lived `HoodieTableMetaClient` for the Review Comment: `getInstantDetails` is missing from this list, yet item 2 above has it building its instant from "the request's metaClient" and reading through the active timeline's `getContentStream`, so it needs one too. It also pays the active-timeline listing that the cost sentence attributes only to the timeline and schema routes. Add it to both the enumeration and the cost model, or state where `getInstantDetails` gets its metaClient. ########## rfc/rfc-94/rfc-94.md: ########## @@ -0,0 +1,662 @@ +<!-- + Licensed to the Apache Software Foundation (ASF) under one or more + contributor license agreements. See the NOTICE file distributed with + this work for additional information regarding copyright ownership. + The ASF licenses this file to You under the Apache License, Version 2.0 + (the "License"); you may not use this file except in compliance with + the License. You may obtain a copy of the License at + + http://www.apache.org/licenses/LICENSE-2.0 + + Unless required by applicable law or agreed to in writing, software + distributed under the License is distributed on an "AS IS" BASIS, + WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. + See the License for the specific language governing permissions and + limitations under the License. +--> + +# RFC-94: Hudi Timeline User Interface (UI) + +## Proposers + +- @voonhous + +## Approvers + +- @danny0405 +- @rahil-c +- @yihua + +## Status + +JIRA: [HUDI-9315](https://issues.apache.org/jira/browse/HUDI-9315) + +## Abstract + +Hudi Timeline metadata is stored as timestamped files representing state transitions of actions like `commit`, +`deltacommit` and `compaction`. These files are accessible via the CLI or a file explorer, but it's hard to visualize +concurrent actions, spot missing transitions, or tell how long each step took. Debugging timeline issues by reading +filenames is tedious. + +This RFC proposes a UI-based timeline visualization tool that parses these metadata files, groups related actions, and +renders them in a time-ordered, interactive view. Users can track the lifecycle of each operation, see concurrency +patterns, and spot anomalies or long-running tasks. The implementation extends `hudi-timeline-service` with new `/v2/` +REST APIs and a static HTML + JavaScript frontend powered by [vis-timeline](https://github.com/visjs/vis-timeline), +served via Javalin's built-in static file serving with zero new Java compile-time dependencies. + +## Background + +Today, we rely on the CLI or direct filesystem inspection to understand timeline state through metadata files. These +files represent different actions (e.g., `deltacommit`, `compaction`) and their lifecycle states (`requested`, +`inflight`, `completed`), encoded in file names like: + +```shell +20250409102118815.deltacommit.inflight +20250409102118815.deltacommit.requested +20250409102118815_20250409102124339.deltacommit +20250409102121593.compaction.inflight +20250409102121593.compaction.requested +20250409102121593_20250409102122232.commit +20250409102124581.deltacommit.inflight +20250409102124581.deltacommit.requested +20250409102124581_20250409102125667.deltacommit +20250409102124612.compaction.inflight +20250409102124612.compaction.requested +20250409102124612_20250409102124892.commit +20250409102127348.deltacommit.inflight +20250409102127348.deltacommit.requested +20250409102127348_20250409102128481.deltacommit +20250409102127500.compaction.inflight +20250409102127500.compaction.requested +20250409102127500_20250409102127721.commit +``` + +This works, but has a few problems: + +1. No visibility into concurrency + - Multiple actions (e.g., `deltacommit` and `compaction`) often run concurrently. + - The CLI doesn't help correlate or visualize overlapping operations. +2. Lack of temporal context + - Timestamps are embedded in filenames but are hard to compare visually - year, month and day can be quickly + determined, but minutes and seconds are harder to parse. + - No easy way to tell how long an action took or whether it's stalling unless you manually calculate the difference + between requested and completion time. +3. Hard to spot inconsistencies or missing states + - An `inflight` compaction without a corresponding `commit` can indicate a starved/stuck compaction, which usually + blocks archiving/cleaning. + - These gaps are easy to miss when scanning filenames. + +On top of that, all timeline files are now stored as Avro binaries. Inspecting their contents requires custom Avro +readers to convert the binaries to JSON. + +## Scope + +This RFC covers visualization of metadata available in Hudi tables. All features are **READ-ONLY** - there is no support +for starting or spawning jobs that mutate a Hudi table. + +Alongside the timeline, the UI surfaces two additional read-only metadata views: the table's configuration +(`hoodie.properties`) and its schema-change history. + +The following are **out of scope**: + +- **Archived timeline:** Only the active timeline is rendered. Loading instants from LSM-based archive files is left for + future work. +- **Metadata table overlay:** The metadata table's own timeline is not shown alongside the main table timeline. +- **Write/mutation operations:** The UI cannot trigger compactions, clustering, or any write action. +- **Authentication/authorization:** No access control is added. The timeline server is assumed to run in a trusted + network, same as today. + + **Threat model:** The timeline and instant-detail views are `/v1`-parity - they read the same active-timeline and + filesystem metadata the existing `/v1/` REST APIs already serve, on the same network interface (the server binds to + all interfaces on the driver/standalone host). Two views widen the read surface beyond `/v1`, whose routes serve only + file-slice/base-file/timeline DTOs: the table-config view (`/v2/hoodie/view/table/config`) returns the full + `hoodie.properties` via `HoodieTableConfig.getProps()`, and the schema-history view + (`/v2/hoodie/view/table/schema/history`) exposes current and historical table schemas. Table properties can reference + sensitive material - KMS endpoints, lock-provider connection strings, external key/vault paths - though they rarely + embed secrets directly. The first cut serves table config unfiltered (sorted, as-is); the same content is already + readable by anyone with filesystem access to `.hoodie/hoodie.properties`. The primary control is that all UI routes, + including these two, are gated behind `--enable-ui` (off by default), with the server assumed to run on a trusted + network; a redacting/allowlisted config view is a possible future refinement for less-trusted interfaces. The UI adds + no write or mutation capability. Operators on untrusted networks should front the server with a reverse proxy or + restrict it to a private interface / localhost via network policy. + +## Implementation + +Keeping the implementation lightweight is a priority - we should add as few dependencies as possible. Changes go into +the existing `hudi-timeline-service` module, which contains a Javalin web-application that caches filesystem metadata of +a Hudi table for job executors during tagging/writing. + +The first cut runs the UI on the Timeline Server in **STANDALONE** mode (see [Configuration](#configuration)) and is +self-contained within `hudi-timeline-service`. Enabling the UI on the **EMBEDDED** timeline server inside a Spark +driver, together with a Spark UI tab, requires cross-module wiring (`hudi-client-common`, `hudi-spark-client`); it is +designed below but deferred to a follow-up to keep the initial PR small and focused. The standalone UI lands first; the +embedded/Spark linking lands next. + +The Hudi Timeline UI has two parts: the frontend and backend. + +### Architecture + +The timeline server can run standalone or embedded inside a Spark driver. In embedded mode, a tab in the Spark UI links +directly to the Hudi Timeline UI. The embedded mode and Spark UI tab (right side of the diagram below) are a planned +follow-up; the first cut is standalone-only. + +```mermaid +graph LR + Browser["Browser"] + + subgraph Driver["Standalone / Spark Driver"] + subgraph TimelineServer["Javalin (Timeline Server)"] + Static["/ui entry + /ui/static/*\n(HTML, JS, CSS)"] + API["/v2/hoodie/view/* - TimelineHandler"] + Meta["HoodieTableMetaClient\n(active timeline, config, schema)"] + + API --> Meta + end + + subgraph SparkUI["Spark UI (:4040) - embedded mode (follow-up)"] + direction TB + SparkUIPad[ ] ~~~ Tabs["[Jobs] [Stages] ... [Hudi Timeline]"] + end + + style SparkUIPad fill:none,stroke:none,color:none + + Tabs -- "link" --> Static + end + + Browser -- "HTTP" --> Static + Browser -- "HTTP" --> API + Browser -. "HTTP\n(embedded mode)" .-> SparkUI +``` + +There are two categories of requests: + +1. **Static file requests** - Javalin serves JavaScript, CSS, and library assets from the classpath + (`src/main/resources/public/`) under the `/ui/static/` URL prefix; `UiHandler` serves `index.html` at `/ui`. No + server-side rendering or template engine is needed. +2. **REST API requests** (`/v2/hoodie/view/*`) - `TimelineHandler` processes these requests, reading from a short-lived + `HoodieTableMetaClient` built for the request's basepath - its `getActiveTimeline()` for the timeline routes, and + table config/schema for the config/schema routes - and returning JSON. + +### Frontend + +The frontend is static HTML pages with vanilla JavaScript, similar to the Spark Web UI. Javalin's built-in static file +serving handles files from the classpath - no template engine (e.g., Thymeleaf) is needed and no new Java compile-time +dependencies are added. + +No frontend build pipeline (npm, webpack, vite) is needed. Contributing to the UI requires only a text editor. Three +libraries are vendored as static assets: vis-timeline (timeline rendering), Bootstrap 5 (layout/styling), and renderjson +(collapsible JSON in the detail panel). + +#### File Structure + +``` +hudi-timeline-service/src/main/resources/public/ +├── index.html # Landing page with basepath input form +├── js/ +│ └── timeline.js # vis-timeline initialization and REST API calls +├── css/ +│ └── style.css # Basic styling +└── lib/ # Vendored third-party assets (see Dependency Impact) + ├── vis-timeline/ # Timeline rendering (Apache-2.0 OR MIT) + │ ├── vis-timeline-graph2d.min.js + │ └── vis-timeline-graph2d.min.css + ├── bootstrap/ # Layout/styling (MIT) + │ ├── bootstrap.bundle.min.js + │ └── bootstrap.min.css + └── renderjson/ # Collapsible JSON detail panel (ISC) + └── renderjson.js +``` + +#### JavaScript Delivery: Bundled, No External Calls + +All three libraries are served from bundled copies under `/ui/static/lib/` (`/ui/static/lib/vis-timeline/`, +`/ui/static/lib/bootstrap/`, `/ui/static/lib/renderjson/`). The UI makes no external network calls, so it works out of +the box in air-gapped and security-conscious deployments with no extra configuration. The bundled, minified assets add +~890KB to the JAR (vis-timeline ~575KB, Bootstrap 5 ~305KB, renderjson ~11KB). + +Pinning a vendored copy (rather than loading from a CDN) keeps the UI deterministic and avoids a runtime dependency on +an external host being reachable. If automatic patch updates are wanted later, a CDN source can be added as an opt-in +config flag without changing this default. + +#### vis-timeline Configuration + +The timeline is configured with groups and items that map to Hudi's timeline model: + +- **Groups:** One row per action type - `commit`, `deltacommit`, `compaction`, `clean`, `rollback`, `clustering`, + `savepoint`, `logcompaction`, `indexing`, `restore`, `replacecommit`. These correspond to the actions in + `HoodieTimeline.VALID_ACTIONS_IN_TIMELINE`. +- **Items:** Completed instants are rendered as range bars spanning from `requestedTime` to `completionTime`. + Non-completed instants (requested or inflight) are rendered as point items at `requestedTime`. +- **Color coding:** Items are colored by state: + - Green -> `COMPLETED` + - Yellow -> `INFLIGHT` + - Red -> `REQUESTED` +- **Tooltip:** On hover, shows the action type, requested time, completion time, and duration. +- **Click handler:** Clicking an instant fetches its detail via `/v2/hoodie/view/timeline/instant` and shows the + deserialized JSON in a detail panel below the timeline. + +### Backend + +A `hudi-timeline-service` instance already serves filesystem metadata for multiple table basePaths since the +`FileSystemView`s are cached in a map keyed by basepath. + +We extend this module with `/v2/` APIs that serve the UI's timeline, config and schema metadata, reading each table +through a short-lived `HoodieTableMetaClient` built per request (see [Handler Design](#handler-design)). + +#### API Specification + +| Method | Path | Parameters | Response | Description | +|--------|-----------------------------------------|-----------------------------------------------------------------------|-----------------|----------------------------------------------------------------------------------------------| +| GET | `/v2/hoodie/view/timeline/instants/all` | `basepath` (required) | `TimelineDTOV2` | All active instants (each with requested time, completion time, action, state), wrapped in a timeline DTO | +| GET | `/v2/hoodie/view/timeline/instant` | `basepath`, `instant`, `instantaction`, `instantstate` (all required) | JSON string | Deserialized content of a specific instant's metadata (Avro -> JSON) | +| GET | `/v2/hoodie/view/table/config` | `basepath` (required) | JSON object | The table's `hoodie.properties` (sorted) | +| GET | `/v2/hoodie/view/table/schema/history` | `basepath` (required), `limit` (optional, default 200, max 1000) | JSON object | Current schema, per-commit schema-change history from the last `limit` commits, and `.schema` internal-schema history when present | + +Static assets (JS, CSS, library files) are served from the classpath directory `src/main/resources/public/`, mounted +under the `/ui/static/` URL prefix via Javalin's static-files `hostedPath` (e.g., `/ui/static/js/timeline.js`, +`/ui/static/lib/...`). Namespacing everything UI under `/ui` keeps the UI surface from colliding with `/v1/`, `/v2/`, or +any future module-registered routes on the same Javalin instance, rather than reserving root prefixes like `/js`, +`/css`, and `/lib`. `UiHandler` additionally registers `GET /ui`, which returns `index.html` (with asset links pointing +at `/ui/static/...`) to give the UI a stable entry URL. + +**On response size and pagination:** `GET /v2/hoodie/view/timeline/instants/all` returns the full active timeline. The +active timeline is bounded by archiving (the unbounded archived timeline is out of scope), so instant counts are +typically modest. The first cut intentionally returns all active instants and relies on client-side zoom/scroll and +filtering for navigation. If active-timeline sizes become a concern, the endpoint can be extended additively with +optional `from`/`to` time-range query params (and/or a `limit`) without breaking the existing contract. + +#### DTO Design + +The UI's timeline endpoint returns a `TimelineDTOV2` built from two v2 DTOs in a `v2` package, leaving the existing +`/v1/` API contract untouched. + +The v1 `InstantDTO` already carries everything needed to render range bars - `fromInstant` populates both +`requestedTime` and `completionTime` from `HoodieInstant` (added under HUDI-9332) - so the UI could consume the v1 +timeline DTO directly. The v2 DTOs are not about exposing new fields; they are a deliberate, low-cost choice to give the +new `/v2/` API a cleaner JSON contract: + +- **`InstantDTOV2`** (`o.a.h.common.table.timeline.dto.v2`) - the same source fields as v1, with UI-oriented JSON keys: + - `action` - the action type (e.g., `commit`, `deltacommit`, `compaction`) + - `requestedTime` (JSON `requestTs`) - requested timestamp (`HoodieInstant.requestedTime()`) + - `completionTime` (JSON `completionTs`) - completion timestamp (`HoodieInstant.getCompletionTime()`), null for + non-completed instants + - `state` - the instant state (`REQUESTED`, `INFLIGHT`, `COMPLETED`) + + Versus v1, this renames `requestedTime`/`completionTime` to `requestTs`/`completionTs` and drops v1's redundant legacy + `ts` field (a duplicate of the requested time that the UI does not need). +- **`TimelineDTOV2`** - wraps a `List<InstantDTOV2>` (`instants`); this is what `/v2/hoodie/view/timeline/instants/all` + returns. + + Both v2 DTOs carry the `V2` suffix to mirror the repo's versioned-class convention (`versioning/v1`/`v2` with + `InstantGeneratorV1`/`V2`, `BaseTimelineV1`/`V2`) and to avoid a simple-name clash with the existing `dto.InstantDTO` + that `TimelineHandler` still imports for the v1 routes. + +#### Handler Design + +The v2 endpoints are served by the existing `TimelineHandler` (which already serves the v1 timeline routes); a separate +`UiHandler` serves only the UI entry page. + +`TimelineHandler` methods: + +1. `getTimelineV2(basePath)` - maps `getActiveTimeline()` from the request's `HoodieTableMetaClient` to a + `TimelineDTOV2`. The active timeline carries every `VALID_ACTIONS_IN_TIMELINE` action in all states + (requested/inflight/completed), which the vis-timeline groups and requested/inflight point items require. The + `FileSystemView` timeline (`getFileSystemView(basePath).getTimeline()`) cannot be used here: it is the write timeline + filtered to completed plus (log)compaction instants, so it drops `clean`/`rollback`/`savepoint`/`restore`/`indexing` + and every requested/inflight state. +2. `getInstantDetails(basePath, instant, action, state)` - reads the instant's Avro content via the active timeline's + `getContentStream(instant)` (the non-deprecated reader method; `getInstantDetails()` is `@Deprecated`) and + deserializes it to JSON. The instant is built with the request's metaClient via `metaClient.getInstantGenerator()`; + a malformed `state`/`action` returns 400, a read failure is logged and returns 500. +3. `getTableConfig(basePath)` - returns the table's `hoodie.properties` as a sorted JSON object. +4. `getSchemaHistory(basePath, limit)` - reconstructs schema evolution from two sources; see + [Schema-History Reconstruction](#schema-history-reconstruction) below. + +`getTimelineV2`, `getTableConfig` and `getSchemaHistory` each build a short-lived `HoodieTableMetaClient` for the +request's basepath, read from it, and discard it - no metaClient is shared across Javalin's request threads. At +human-click frequency the construction cost (one `hoodie.properties` read, plus one active-timeline listing for the +timeline and schema routes) is negligible, and a fresh per-request instance is always current and keeps each request's +read self-consistent. A long-lived per-basepath cache is deliberately avoided: the data must be re-read on every request +anyway, so caching the metaClient would save little while forcing an in-place `reloadActiveTimeline()` / +`reloadTableConfig()` on a mutable object shared across concurrent same-basepath requests. `HoodieTableMetaClient` marks +its individual accessors `synchronized`, but a compound reload-then-read is not one critical section, so a concurrent +reload could swap the snapshot between one request's reload and its read - a fresh instance sidesteps that entirely. A +TTL is likewise avoided: at this request rate it would save no meaningful work and would only add a staleness window. The +UI also surfaces a **Refresh** control on the Table Config and Schema History tabs; because the server reads fresh on +every request, the button simply re-issues the fetch. The timeline view is fresh on every request too; instant details +are immutable once written and need no refresh. + +`UiHandler` registers `GET /ui`, returning `/public/index.html` from the classpath as the UI entry page. + +#### Schema-History Reconstruction + +`getSchemaHistory` combines both schema sources Hudi maintains, so it returns something useful whether or not the table +uses schema evolution: + +- **`currentSchema`** - the current table schema from `TableSchemaResolver.getTableSchema()`; `null` if it cannot be + resolved. +- **`history`** - walks the completed commits timeline (`commit`/`deltacommit`/`replacecommit`), the most recent `limit` + instants only (default 200, capped at 1000), reading each instant's `HoodieCommitMetadata` and taking the schema under + `HoodieCommitMetadata.SCHEMA_KEY` (the `schema` entry in commit `extraMetadata`). An entry (`instant`, + `completionTime`, `action`, `schema`) is recorded only when the schema differs from the previous instant's, so runs of + commits carrying the same schema collapse to one change entry. Instants whose metadata cannot be read are skipped. +- **`internalSchemaHistory`** (optional) - when `InternalSchema` is in use, the `.hoodie/.schema/` history string from + `FileBasedInternalSchemaStorageManager.getHistorySchemaStr()` is added for richer evolution tracking. It is omitted + when the `.schema` directory is absent - the common case for tables that never enabled schema evolution. + +**Cost model:** one schema resolve, at most `limit` completed-commit metadata reads (bounded further by the active +timeline, since the archived timeline is out of scope), and one `.schema` history-file read. A table that never evolved +its schema resolves `currentSchema`, collapses `history` to a single entry (or none if no commit recorded a schema), and +omits `internalSchemaHistory` - no extra scanning and no error. + +#### Registration in RequestHandler + +The v2 routes are registered following the existing pattern: + +- The v1 timeline routes remain registered unconditionally in `registerTimelineAPI()`. +- The v2 UI routes are registered in `registerTimelineV2API()`, called from `register()` only when `--enable-ui` is set. + `UiHandler` (serving `/ui`) and the static-file serving are gated by the same flag. + +#### Error Handling + +- **Invalid basepath** -> HTTP 400 with a descriptive error message (e.g., "Not a valid Hudi table path"). +- **Empty timeline** -> Returns an empty list `[]`. The frontend displays "No instants found". +- **Failed instant detail read** -> HTTP 500 with error details (e.g., Avro deserialization failure). + +### Feature + +The first cut presents three read-only tabs for a Hudi table: **Timeline**, **Table Config**, and **Schema History**. + +The permitted user actions are: + +1. User is able to input a Hudi table basepath +2. User is able to click submit after inputting Hudi table basepath +3. The timeline of the Hudi table is rendered +4. User is able to scroll through timeline (horizontally) +5. User is able to zoom in and out of timeline +6. User is able to hover over instant for more details +7. User is able to click on a specific instant and the JSON string of the timeline details are rendered +8. User is able to view the table's configuration (`hoodie.properties`) in the Table Config tab +9. User is able to view the table's schema and schema-change history in the Schema History tab +10. User is able to click a **Refresh** control on the Table Config and Schema History tabs to re-pull the latest values + (the server reads the table config / active timeline fresh on each request) + +Each action type occupies its own horizontal row so concurrent actions are visually separated. Completed instants appear +as horizontal bars whose width represents duration (requested -> completed). Inflight and requested instants appear as +point markers. Color indicates state: green for completed, yellow for inflight, red for requested. + +### Examples + +Proof of concept (PoC) snapshots: + +**Main Page with Timeline Rendered** + + +**Hovering Over an Instant** + + +**Selecting an Instant** + + +## Configuration + +### Standalone Mode + +To start the Timeline Server in standalone mode with the UI enabled: + +```shell +java -cp hudi-timeline-server-bundle-*.jar \ + org.apache.hudi.timeline.service.TimelineService \ + --server-port 26754 \ + --enable-ui +``` + +Once started, the UI is accessible at `http://localhost:26754/ui`. + +The server port is configurable via the existing `--server-port` (or `-p`) flag (default: `26754`). The `--enable-ui` +flag controls whether the UI static files, the `/ui` page, and the `/v2/hoodie/view/` UI API endpoints are registered. +When the flag is not set, the timeline server behaves exactly as it does today - no UI-related routes are added. + +### Embedded Mode (Spark-Shell / Spark Driver) + +> **Status: deferred to a follow-up.** Embedded-mode UI enablement is intentionally split out of the initial PR to keep +> it small: the standalone UI ships first, then the embedded server is wired to enable it. The design below is retained +> for that follow-up. + +When running Hudi inside a Spark application, the `EmbeddedTimelineService` already starts a timeline server within the +driver process. The UI can be enabled on this embedded server by setting a Spark configuration property: + +``` +hoodie.embed.timeline.server.ui.enable = true +``` + +This property defaults to `false`. When set to `true`, the embedded timeline server registers the same UI routes and +static file serving as the standalone mode. + +#### Starting from spark-shell + +```shell +spark-shell \ + --packages org.apache.hudi:hudi-spark3-bundle_2.12:1.2.0 \ + --conf "hoodie.embed.timeline.server.ui.enable=true" +``` + +Once a write operation initializes the `EmbeddedTimelineService`, the UI becomes available at +`http://<driver-host>:<embedded-server-port>/ui`. The embedded server binds a free port by default +(`hoodie.embed.timeline.server.port` = `0`), and the bound port is not written back to that property - read it from the +startup log line (`Started embedded timeline server at <host>:<port>`), or from the resolved +`FileSystemViewStorageConfig` remote-server port that `EmbeddedTimelineService` propagates it to. + +#### Starting from a Spark application (driver) + +Set the property programmatically on `HoodieWriteConfig` before creating the write client: + +```java +HoodieWriteConfig config = HoodieWriteConfig.newBuilder() + .withPath(basePath) + .withEmbeddedTimelineServerEnabled(true) + .withEmbeddedTimelineServerUIEnabled(true) // enables UI on embedded server + // ... other configs + .build(); +``` + +The UI is available for the lifetime of the `EmbeddedTimelineService` - it starts when the write client initializes and +stops when the client or `SparkContext` is closed. + +## Spark UI Tab Integration + +> **Status: deferred to a follow-up.** The Spark UI tab depends on embedded-mode enablement and cross-module Spark APIs, +> so it is split out of the initial PR for the same reason. The design below is retained for that follow-up. + +When the `EmbeddedTimelineService` starts with the UI enabled inside a Spark application, a "Hudi Timeline" tab is +registered in the Spark web UI (typically at `http://localhost:4040`). This gives users a single place to discover and +access the Hudi Timeline UI without needing to know the embedded server's port. + +### Approach + +A custom class extending Spark's `WebUITab` is added to the `hudi-spark-client` module. The tab contains a single +`WebUIPage` that renders a link to the Hudi Timeline UI running on the embedded timeline server at +`http://<driver-host>:<timeline-server-port>/ui`. + +The link approach is chosen over embedding the UI in an iframe to avoid layout and scrolling issues within the Spark UI +shell. Clicking the link opens the full Hudi Timeline UI in a new browser tab, providing the complete interactive +experience. + +### Multiple Tables in One Application + +A Spark application can write to multiple Hudi tables. The embedded timeline server is shared across them: when +`hoodie.embed.timeline.server.reuse.enabled` is set, `EmbeddedTimelineService` keeps a single server per driver and +tracks the set of basepaths using it (`EmbeddedTimelineService.basePaths`), adding each table on its first write. The +backend already caches one `FileSystemView` per basepath, and each UI request builds a `HoodieTableMetaClient` for its +own basepath, so that single server serves every table. + +The tab therefore links to a single UI instance rather than registering one tab per table. The user selects which +table to view inside the UI via the basepath input form (persisted in the `?path=` query parameter). Because the +server already knows the set of basepaths it serves, a natural follow-up is to pre-populate that input as a dropdown of +registered basepaths so users pick from known tables instead of typing. + +Tab registration is guarded so the "Hudi Timeline" tab is registered once per driver, avoiding duplicate tabs when the +server is reused across tables. + +### Registration and Lifecycle + +``` +SparkContext starts + └─> EmbeddedTimelineService starts (with UI enabled) + └─> HudiTimelineTab registered via SparkUI.attachTab() + +SparkContext stops / write client closes + └─> EmbeddedTimelineService stops + └─> HudiTimelineTab detached via SparkUI.detachTab() +``` + +Registration is triggered by `EmbeddedTimelineService` after the embedded server has started successfully, through the +provider SPI described in [Module Placement and Dependency Inversion](#module-placement-and-dependency-inversion) below +(`EmbeddedTimelineService` itself holds no Spark types). The tab is detached during shutdown to ensure clean cleanup. If +the Spark UI is not available (e.g., `spark.ui.enabled=false`), the tab registration is skipped silently. + +### Module Placement and Dependency Inversion + +The Spark UI tab implementation depends on Spark APIs (`WebUITab`, `WebUIPage`), so it must live in `hudi-spark-client`. +`EmbeddedTimelineService`, however, lives in `hudi-client-common`, and the module dependency runs one way only: +`hudi-spark-client` depends on `hudi-client-common`, never the reverse. `EmbeddedTimelineService` therefore cannot +reference the Spark tab class - or even `HoodieSparkEngineContext` - directly; doing so would not compile. + +Registration is inverted through a `ServiceLoader` SPI, mirroring how `hudi-common` already discovers +`HoodieTableFormat` implementations (`ServiceLoader.load(HoodieTableFormat.class)` in `HoodieTableConfig`): + +- An engine-agnostic provider interface is defined in `hudi-client-common` (no Spark types on its signature), e.g.: + + ```java + // hudi-client-common: org.apache.hudi.client.embedded + public interface TimelineServerUITabProvider { + void register(HoodieEngineContext context, String serverHost, int serverPort); + void unregister(); + } + ``` + +- `hudi-spark-client` supplies the implementation (`SparkTimelineServerUITabProvider`), registered via + `META-INF/services/org.apache.hudi.client.embedded.TimelineServerUITabProvider`. Only this implementation touches + Spark APIs: it casts the `HoodieEngineContext` to `HoodieSparkEngineContext`, obtains the `SparkContext`/`SparkUI`, + and calls `attachTab()` / `detachTab()` with the `WebUITab`. +- After the embedded server starts, `EmbeddedTimelineService` runs + `ServiceLoader.load(TimelineServerUITabProvider.class)` and invokes the single provider found, if any, passing the + started server's host and port. When no provider is on the classpath (non-Spark engines) or the Spark UI is + unavailable (handled inside the impl, e.g. `spark.ui.enabled=false`), registration is skipped silently. The loaded + provider instance is retained so the matching `unregister()` runs at shutdown. + +This keeps `hudi-client-common` free of any Spark compile-time dependency while letting the Spark module supply the tab. + +## Dependency Impact + +- **Zero new Java compile-time dependencies.** The frontend uses Javalin's built-in static file serving; no template + engine is added. +- **Three vendored frontend libraries (~890KB total)** bundled as static resources under + `src/main/resources/public/lib/`. All are ASF Category A licenses and may be redistributed in a release: + - **vis-timeline** (`lib/vis-timeline/`, ~575KB) - timeline rendering. Dual-licensed Apache-2.0 OR MIT. + - **Bootstrap 5** (`lib/bootstrap/`, ~305KB) - layout and styling. MIT. + - **renderjson** (`lib/renderjson/`, ~11KB) - collapsible JSON in the detail panel. ISC. +- **LICENSE/NOTICE obligations.** Each vendored library needs a "This product bundles ..." stanza in the source-release + top-level `LICENSE` (and in the `hudi-timeline-server-bundle` LICENSE, since the assets ship inside that JAR) naming + the library, its license, and its copyright, with the full MIT/ISC license text inlined the same way existing bundled + code is handled in `LICENSE`. The minified files already carry their upstream copyright headers, which must be + preserved. No `NOTICE` changes are required: MIT and ISC do not mandate NOTICE entries, and vis-timeline is taken + under its MIT option (ASF policy discourages adding MIT/ISC copyrights to `NOTICE`); were vis-timeline instead taken + under Apache-2.0, any upstream `NOTICE` content it ships would have to be propagated. +- **Spark UI tab (planned follow-up):** Will use existing `spark-core` APIs (`WebUITab`, `WebUIPage`), already provided + in `hudi-spark-client`. No new JARs are added. +- **No impact on Spark/Flink bundles.** `hudi-timeline-server-bundle` is a separate artifact; adding static resources Review Comment: `hudi-timeline-service` is a compile-scope dependency of `hudi-client-common`, and `hudi-spark-bundle`, `hudi-flink-bundle`, `hudi-utilities-bundle` and `hudi-kafka-connect-bundle` all list `org.apache.hudi:hudi-timeline-service` in their shade `artifactSet`. Their `<filters>` exclude only signature files, `META-INF/services/javax.*` and `**/*.proto`, so everything under `src/main/resources/public/` is unpacked into each of those JARs. The module has no `src/main/resources` today, so the ~890KB of vendored assets is net-new payload in every engine bundle, not only `hudi-timeline-server-bundle`. Restate this bullet accordingly, and widen the LICENSE/NOTICE bullet above to cover those bundles. If the assets are meant to stay out of the engine bundles, that needs an explicit shade filter excluding `public/**` in each bundle pom, which is worth specifying here. -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected]
