JanKaul commented on code in PR #11041: URL: https://github.com/apache/iceberg/pull/11041#discussion_r3014525620
########## format/view-spec.md: ########## @@ -160,7 +178,122 @@ 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 property "refresh-state" is set on the [snapshot summary](https://iceberg.apache.org/spec/#snapshots) property of every storage table snapshot to determine the freshness of the precomputed data of the storage table. + +| Requirement | Field name | Description | +|-------------|-----------------|-------------| +| _required_ | `refresh-state` | A [refresh state](#refresh-state) record stored as a JSON-encoded string | + +#### Freshness + +A materialized view is "fresh" when the storage table adequately represents the logical query definition of the view. +Since different systems define freshness differently, it is left to the consumer to evaluate freshness based on its own policy. + +**Consumer behavior:** + +When evaluating freshness, consumers: + +- May apply time-based freshness policies, such as allowing a staleness window based on `refresh-start-timestamp-ms`. +- May compare the `source-states` list against the states loaded from the catalog to verify the producer's freshness interpretation. +- May parse the view definition to implement more sophisticated policies. +- When a materialized view is considered stale, can fail, refresh inline, or treat the materialized view as a logical view. +- Should not consume the storage table as it is when the materialized view doesn't meet the freshness criteria. + +**Producer behavior:** + +Producers should provide the necessary information in the [refresh state](#refresh-state) such that consumers can verify the logical equivalence of the precomputed data with the query definition. +Different producers may have different freshness interpretations, based on how much of the refresh state's dependency graph should be evaluated. +Some producers expect the entire dependency graph to be evaluated and therefore include source MV dependencies. Other producers may only expect dependencies in the MV's SQL to be evaluated and therefore do not include dependencies of source MVs. + +When writing the refresh state, producers: + +- Should provide a sufficient list of source states such that consumers can determine freshness according to the producer's interpretation. If the producers interpretation is such that it doesn't rely on the source-states to determine freshness, it may provide an empty list. +- If the source state cannot be determined for all objects (for example, for non-Iceberg tables) may leave the source states list empty. +- If a stored object is reachable through multiple paths in the dependency graph (diamond dependency pattern), the entry with the oldest snapshot-id or version-id must be stored. Review Comment: With regards to freshness, to argument was as follows: - all source tables need to be up-to-date for a storage table to be fresh - if any source table snapshot is out-of-date, the oldest snapshot is also out-of-date - if the oldest snapshot is up-to-date, all other snapshots are up-to-date - the oldest snapshot is enough information to determine freshness in the diamond pattern Your comment is really relevant for incremental processing though. As the information what data has been processed is vital. I think we should then include all source table states, even different snapshots of the same table. -- 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]
