Support SHALLOW CLONE of Iceberg Tables #1522
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vkorukanti
approved these changes
Dec 14, 2022
| // The source relation can be an Iceberg table in form of `catalog.db.table` so we visit | ||
| // a multipart identifier instead of TableIdentifier (which does not support 3L namespace) | ||
| // in Spark 3.3. | ||
| val sourceRelation = new UnresolvedRelation(visitMultipartIdentifier(ctx.source)) |
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Is this something that can be fixed once Delta upgrades to Spark 3.4? If yes, add a comment.
| // the existing files and the newly added files. | ||
| val cloneSourceTable = sourceTbl match { | ||
| case source: CloneIcebergSource => | ||
| // Reuse the existing schema so that the physical name of columns are consistent between |
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Sorry this is not clear. Why do we have to use the schema of the existing table when replacing it? Isn't shallow clone just referencing the existing data files in iceberg table? What does the "existing files" mean here?
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Yeah, but if you are REPLACE on an existing Delta table and since Iceberg use column mapping, we have to make sure the column mapping metadata match during conversion.
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Overview
As a followup to the SHALLOW CLONE support for Delta Lake, it would be great if we could enable SHALLOW CLONE on an Iceberg table as well. This will be a CLONVERT (CLONE + CONVERT) operation, in which we will create a Delta catalog table with files pointing to the original Iceberg table in one transaction.
Motivation
Further details
Similar to SHALLOW CLONE, it will work as follows:
How was this patch tested?
New unit tests.
Does this PR introduce any user-facing changes?
No.