voonhous commented on code in PR #13152: URL: https://github.com/apache/hudi/pull/13152#discussion_r3565970548
########## rfc/rfc-94/rfc-94.md: ########## @@ -0,0 +1,644 @@ +<!-- + 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"] + FSVM["FileSystemViewManager"] + Meta["HoodieTimeline / MetaClient"] + + API --> FSVM --> 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 timeline data from + the `FileSystemViewManager` (and a per-basepath `HoodieTableMetaClient` for table config/schema), 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 to serve the timeline metadata needed by the UI. + +#### 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: + +- **`InstantDTO`** (`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<InstantDTO>` (`instants`); this is what `/v2/hoodie/view/timeline/instants/all` + returns. + +#### 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 `viewManager.getFileSystemView(basePath).getTimeline()` to a `TimelineDTOV2` (the + active timeline's instants, each including completion time). +2. `getInstantDetails(basePath, instant, action, state)` - reads the instant's Avro content via the active timeline's + `getInstantDetails()` and deserializes it to JSON. The instant is created with the timeline's own layout-aware + `InstantGenerator`; 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. + +Both `getTableConfig` and `getSchemaHistory` reuse a `HoodieTableMetaClient` cached per basepath in a +`ConcurrentHashMap`, so repeated requests skip full metaClient construction. A `HoodieTableMetaClient` snapshots its +`tableConfig` and `activeTimeline` at construction and refreshes them only on demand, so a build-once cache would serve +stale config/schema for the lifetime of a long-lived embedded driver. To avoid that, each config/schema request first +reloads the relevant snapshot under a per-basepath guard - `reloadTableConfig()` for `getTableConfig`, +`reloadActiveTimeline()` for `getSchemaHistory` - before reading. These are human-click-frequency views, so the reload +cost (one `hoodie.properties` read plus one timeline listing) is negligible and the response is always current. A TTL is +deliberately not used: at this request rate it would save no meaningful work and would only reintroduce a staleness +window. The UI also surfaces a **Refresh** control on the Table Config and Schema History tabs to re-pull on demand; +because the server reloads on every request, the button simply re-issues the fetch rather than busting a cache. The +timeline and instant-detail views are unaffected - they read the server-synced `FileSystemView`, not the cached +metaClient. + +`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 reloads the table config / active timeline 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 port is logged at startup and can also be +retrieved from the Spark configuration via the `hoodie.embed.timeline.server.port` property. Review Comment: Correct, fixed. Verified: `hoodie.embed.timeline.server.port` defaults to `0` ("picks a free port", HoodieWriteConfig.java:595) and the bound port is never written back to it - `EmbeddedTimelineService` keeps it in `serverPort` (line 180), logs it (181), and propagates it only via `FileSystemViewStorageConfig.withRemoteServerPort()` (210). Reading the property back would give `0`. Reworded the sentence to drop the "retrieved from the Spark configuration" claim and point users at the startup log line (`Started embedded timeline server at <host>:<port>`) or the resolved `FileSystemViewStorageConfig` remote-server port instead. (For the record, the `setValue(EMBEDDED_TIMELINE_SERVER_PORT_NUM, ...)` at HoodieWriteConfig.java:3512 is just the builder setter for a user-requested port, not a runtime write-back, so it doesn't change this.) -- 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]
