stevenzwu commented on code in PR #11041: URL: https://github.com/apache/iceberg/pull/11041#discussion_r2590258037
########## format/view-spec.md: ########## @@ -42,12 +42,28 @@ An atomic swap of one view metadata file for another provides the basis for maki Writers create view metadata files optimistically, assuming that the current metadata location will not be changed before the writer's commit. Once a writer has created an update, it commits by swapping the view's metadata file pointer from the base location to the new location. +### Materialized Views + +Materialized views are a type of view with precomputed results from the view query stored as a table. +When queried, engines may return the precomputed data for the materialized views, shifting the cost of query execution to the precomputation step. + +Iceberg materialized views are implemented as a combination of an Iceberg view and an underlying Iceberg table, the "storage-table", which stores the precomputed data. +Materialized View metadata is a superset of View metadata with an additional pointer to the storage table. The storage table is an Iceberg table with additional materialized view refresh state metadata. +Refresh metadata contains information about the "source tables" and/or "source views", which are the tables/views referenced in the query definition of the materialized view. +During read time, a materialized view (storage table) can be interpreted as "fresh", "stale" or "invalid", depending on the following situations: +* **fresh** -- The `snapshot_id`s of the last refresh operation match the current `snapshot_id`s of all the source tables, OR all source table snapshots that differ from the last refresh have timestamps within a configured staleness window. +* **stale** -- The `snapshot_id`s do not match for at least one source table and at least one differing snapshot has a timestamp outside the configured staleness window, indicating that a refresh operation needs to be performed to capture the latest source table changes. Review Comment: I still think it might be better to move the status part to a separate section (`Status interpretation`) in the end (like after the refresh state section). Would be better to describe the refresh state and the max staleness config first before talking about how to determine fresh/stale. -- 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]
