JanKaul commented on code in PR #11041: URL: https://github.com/apache/iceberg/pull/11041#discussion_r3968684870
########## format/view-spec.md: ########## @@ -160,7 +178,116 @@ Each entry in `version-log` is a struct with the following fields: | _required_ | `timestamp-ms` | Timestamp when the view's `current-version-id` was updated (ms from epoch) | | _required_ | `version-id` | ID that `current-version-id` was set to | -## Appendix A: An Example +#### Storage Table Identifier + +The table identifier for the storage table that stores the precomputed results. + +| Requirement | Field name | Description | +|-------------|----------------|-------------| +| _required_ | `namespace` | A list of strings for namespace levels | +| _required_ | `name` | A string specifying the name of the table | + +### Storage table metadata + +This section describes additional metadata for the storage table that supplements the regular table metadata and is required for materialized views. +The `refresh-state` property is set on the [snapshot summary](https://iceberg.apache.org/spec/#snapshots) property of a storage table snapshot to provide information about the state of the precomputed data. + +| Requirement | Field name | Description | +|-------------|-----------------|-------------| +| _optional_ | `refresh-state` | A [refresh state](#refresh-state) record stored as a JSON-encoded string | + +#### Freshness + +A materialized view is **fresh** when the storage table represents the result of the current view query. However, consumers may still decide to consume from a stale storage table based on their own policies. + +A change to the materialized view's definition produces a new `view-version-id`; any storage-table snapshot recorded at a prior `view-version-id` is invalid and should not be consumed until refreshed. + +#### Refresh state + +The refresh state record captures the state of dependencies that the producer chose to track from the materialized view's dependency graph. A dependency is recorded in `source-states` as either a `table` entry (a source table or an source materialized view's storage table) and/or a `view` entry. Source materialized views can be stored as a `view` and a `table` entry. + +The refresh state has the following fields: + +| Requirement | Field name | Description | +|-------------|------------------------------|-------------| +| _required_ | `view-version-id` | The `version-id` of the materialized view when the refresh operation was performed | +| _required_ | `source-states` | A list of [source state](#source-state) records capturing the dependencies the producer chose to track; may be empty | +| _required_ | `refresh-start-timestamp-ms` | A timestamp of when the refresh operation was started | + +##### Producer: Recording Refresh State + +Producers may selectively choose a subset of their dependencies to record — for example, skipping non-Iceberg sources or recording an empty list. See [Appendix B](#appendix-b-what-counts-as-a-dependency) for strategies on how to store dependency state. + +When writing the refresh state, producers: + +- **Must** record `view-version-id` and `refresh-start-timestamp-ms`. +- **Should** include all distinct source states for the inputs they chose to track if they are reachable through multiple path in the dependency graph. +- **May** leave `source-states` empty (e.g., when sources are non-Iceberg or freshness is determined by a mechanism outside this spec). + +##### Consumer: Evaluating Refresh State + +Consumers may use any combination of the following to assess the state of dependencies used to produce the storage table. + +- **Recency policy.** Accept the storage table when `refresh-start-timestamp-ms` falls within a staleness window. A recency policy bounds data age but does not establish freshness. +- **Trust the recorded `source-states`.** Compare each entry against the current catalog state — `snapshot-id` for tables, `version-id` for views, optionally recursive verification for source materialized views recorded by their storage tables. Also confirm that the recorded `view-version-id` equals the materialized view's current `view-version-id`. +- **Verify by parsing the view query.** Derive the dependency set from the SQL and confirm every dependency is covered by `source-states` and matches the current state. Treat any uncovered dependency as undetermined. + +If a consumer's assessment passes, it reads from the storage table. If not, the consumer may fail the query, evaluate the view query directly, or apply another strategy. + +#### Source state + +Source state records capture the state of objects referenced by a materialized view. Each record has a `type` field that determines its form: + +| Type | Description | +|---------|-------------| +| `table` | An Iceberg table — either a source table in the dependency graph, or the storage table of a source materialized view | +| `view` | An Iceberg view in the dependency graph | + +A source materialized view may be recorded as a `view` entry referencing its view metadata and one ore more `table` entries referencing its storage table or other source tables. These source table entries might be determined by recursively expanding its own dependencies. + +#### Source table state + +A source table record captures the state of a source table (including a source materialized view's storage table) at the time of the last refresh operation. + +| Requirement | Field name | Description | +|-------------|---------------|-------------| +| _required_ | `type` | A string that must be set to `table` | +| _required_ | `name` | A string specifying the name of the source table | +| _required_ | `namespace` | A list of strings for namespace levels | +| _optional_ | `catalog` | An optional name of the catalog. If not set, the catalog is the same as the materialized view's | +| _required_ | `uuid` | The uuid of the source table | +| _required_ | `snapshot-id` | The snapshot-id of the source table that was read during the refresh operation | Review Comment: I don't think we have covered that scenario, thanks for bringing it up. The reason for not using the `metadata-file-location` was that iceberg generally wants to move the REST catalog and potentially deprecate the metadata.json file at some point. Yeah, I think your strategy for detecting schema drift should work. We should probably add it to the spec. -- 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] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
