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Posted to issues@iceberg.apache.org by "waterWang (via GitHub)" <gi...@apache.org> on 2026/08/16 05:18:41 UTC
[PR] fix: handle empty struct in CompareSchemasVisitor.struct() [iceberg]
waterWang opened a new pull request, #17683:
URL: https://github.com/apache/iceberg/pull/17683
Fixes #17650
## Problem
`CompareSchemasVisitor.struct()` computes its result as:
```java
Result result = fields.stream().reduce(Result::merge).orElse(Result.SCHEMA_UPDATE_NEEDED);
```
For a struct with zero fields, the `reduce` is empty, so `orElse(SCHEMA_UPDATE_NEEDED)` always fires. Consequently any schema containing an empty struct (e.g. derived from an Avro union whose branch is a zero-field marker record) can never compare `SAME` with any table schema — including a table created from that exact schema.
In the Dynamic Sink this is fatal: `TableUpdater.findOrCreateSchema` sees `SCHEMA_UPDATE_NEEDED`, applies `EvolveSchemaVisitor` (a no-op here), commits, re-compares — still `SCHEMA_UPDATE_NEEDED` — and `TableMetadataCache.schema()` caches and returns `NOT_FOUND`, whose `resolvedTableSchema()` is null.
## Fix
Change `orElse(Result.SCHEMA_UPDATE_NEEDED)` to `orElse(Result.SAME)` — when both structs have zero fields, they are semantically identical.
## Changes
- `flink/v1.20/flink/src/main/java/.../CompareSchemasVisitor.java`
- `flink/v2.0/flink/src/main/java/.../CompareSchemasVisitor.java`
- `flink/v2.1/flink/src/main/java/.../CompareSchemasVisitor.java`
All three versions had the same bug (identical content).
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Re: [PR] fix: handle empty struct in CompareSchemasVisitor.struct() [iceberg]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #17683:
URL: https://github.com/apache/iceberg/pull/17683#issuecomment-5706538216
This pull request has been marked as stale due to 30 days of inactivity. It will be closed in 1 week if no further activity occurs. If you think that’s incorrect or this pull request requires a review, please simply write any comment. If closed, you can revive the PR at any time and @mention a reviewer or discuss it on the dev@iceberg.apache.org list. Thank you for your contributions.
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Re: [PR] fix: handle empty struct in CompareSchemasVisitor.struct() [iceberg]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] commented on PR #17683:
URL: https://github.com/apache/iceberg/pull/17683#issuecomment-5824570898
This pull request has been closed due to lack of activity. This is not a judgement on the merit of the PR in any way. It is just a way of keeping the PR queue manageable. If you think that is incorrect, or the pull request requires review, you can revive the PR at any time.
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Re: [PR] fix: handle empty struct in CompareSchemasVisitor.struct() [iceberg]
Posted by "github-actions[bot] (via GitHub)" <gi...@apache.org>.
github-actions[bot] closed pull request #17683: fix: handle empty struct in CompareSchemasVisitor.struct()
URL: https://github.com/apache/iceberg/pull/17683
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