[spark][doc] Add Spark batch union read#3142
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@wuchong @YannByron @luoyuxia please take a look, thank you! |
beryllw
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Apr 22, 2026
| The union read works for both **log tables** and **primary key tables**: | ||
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| - **Log tables**: Combines Fluss log data with lake historical data | ||
| - **Primary key tables**: Merges the latest Fluss snapshot with log changes and lake history to provide the most up-to-date view |
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Combines lake snapshot data with recent KV log changes using sort-merge to provide the most up-to-date view
The phrase "latest Fluss snapshot" may cause confusion, as Fluss has its own internal snapshot concept (used for KV compaction).
beryllw
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Apr 22, 2026
| -- Returns complete view combining Fluss and lake data | ||
| SELECT * FROM fluss_order_with_lake ORDER BY order_key; | ||
| ``` | ||
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May be we could add a note:
Union read requires `scan.startup.mode = full` (default). Non-FULL modes (e.g., `earliest`, `latest`) bypass the lake path and read only from Fluss.
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scan.startup.mode was not used in batch read actually, will fix related codes in another pr.
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Thanks for the PR! Overall LGTM, with a few minor comments. |
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Purpose
Linked issue: close #xxx
Brief change log
Tests
API and Format
Documentation