JeroenSchmidt opened a new pull request, #3649:
URL: https://github.com/apache/iceberg-python/pull/3649
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# Rationale for this change
Adds `ManageSnapshots.fast_forward_branch(from_branch, to_ref)` to advance a
branch to the snapshot referenced by another branch or tag, provided the
current snapshot of `from_branch` is an ancestor of `to_ref`'s snapshot.
The method almost matches the behavior of Apache Iceberg's Java reference
implementation (`SnapshotManager.fastForwardBranch` /
`UpdateSnapshotReferencesOperation.replaceBranch(..., fastForward=true)`)
and, by extension, the Spark `system.fast_forward` stored procedure that
depends on it.
However, while the implementation is very close there is one exception;
```md
Unlike Java's `ManageSnapshots.fastForwardBranch`, this method does not
provide Java-parity for intra-chain semantics.
1) Java maintains a mutable `updatedRefs` map that reflects prior operations
in the same chain, so calling `createBranch` and then
`fastForwardBranch`
on the same ref in one chain observes the freshly-created state.
2) pyiceberg's `ManageSnapshots` accumulates `SetSnapshotRefUpdate` values
without
mutating `table_metadata.refs` between chained calls;
-> The no-op and ancestry checks below operate on committed metadata
only.
-> Callers that need Java-parity behavior should commit between chain
steps.
```
For the sake of scope I left out the changes needed to ensure chain sematic
parity between the java and python.
Would the maintainers like a followup PR or have it included in this PR? My
only worry is that it will increase the complexity of an otherwise
straightforward PR.
## Are these changes tested?
Yes. Both unit tests and integration tests were writen
## Are there any user-facing changes?
Yes. `fast_forward_branch`.
See `mkdocs/docs/api.md` for more details.
<!-- In the case of user-facing changes, please add the changelog label. -->
## Related Issues / Pull Requests
* Related to the closed PR
https://github.com/apache/iceberg-python/pull/2434 (related issue
https://github.com/apache/iceberg-python/issues/2433) ; my PR is only focused
on implementing fast_forward
* Implemented one of the missing features mentioned in
https://github.com/apache/iceberg-python/issues/737 from @sungwy
## LLM Disclosure
PR was written with the assistance of Claude Opus 4.7 (1M context) (effort:
high)
It implemented the majority of the tests I defined. Specifically to assist
with what fixtures to use and how best to write the unit tests in an atomic
fashion appropriate for pyIceberg.
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