Robust schema usage and checks for batch CDF queries #1509
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jackierwzhang
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| * | ||
| * However, if there are schema changes between analysis and execution, since we froze this | ||
| * schema, our schema incompatibility checks will kick in during the scan so we will always | ||
| * be safe - Although it is a notable caveat that user should be aware of because the CDC query |
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are users aware of this? should we update any documentation to make this clearer?
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Nothing is documented yet for this behavior, but we probably should cc @jose-torres
| * may break. | ||
| */ | ||
| private lazy val endingVersionForBatchSchema: Long = endingVersion.map { v => | ||
| // As defined in docs, if ending version is greater than the latest version, we will just use |
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which docs? method docs? public website docs?
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method doc, i could make it clearer.
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| sql( | ||
| s""" | ||
| |ALTER TABLE delta.`${dir.getCanonicalPath}` ADD COLUMN (name string) | ||
| |""".stripMargin) |
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can this be 1 line instead of 4?
scottsand-db
approved these changes
Dec 15, 2022
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Description
Properly handle read-incompatible schema changes when querying batch CDF (e.g.
table_changes()TVF, and SQL/DF APIs).Right now, batch CDF is almost always serving past data using the latest schema, but the latest schema may not be read-compatible with the data files.
this PR introduces the following:
changeDataFeed.defaultSchemaModeForColumnMappingTablethat can be set toendVersion,latestorlegacy. Iflegacyit would fallback to the current behavior in which either latest schema is used or a time-travel version schema is used, ifendVersionis set, we will use the end version's schema to serve the batch and iflatestis set, the latest schema will always be used. Note, this is orthogonal to 1), checks will be triggered all the time to ensure read-compatibility, even whenendVersionis used.versionOfis specified. Apparently ppl can time-travel the schema during querying batch CDF, this is probably unintentional, but since it exists, i explicitly blocked two options from being used concurrently.How was this patch tested?
New Unit tests.
Does this PR introduce any user-facing changes?
No