[HaHaJeff]

Purpose

Enable partial-update for primary-key realtime writes by reusing the existing merge functions and options used by the ordinary Writer.

Related issue (tracked separately): #524

• Allow PARTIAL_UPDATE alongside DEDUPLICATE, preserving the existing deduplicate ignore-delete restrictions. Standalone aggregation and first-row engines remain unsupported.
• Reuse framework merge logic for prepared readers, sequence groups, field aggregation, and configured delete handling. The store only stores, sorts, and spills; merging remains the framework's responsibility.
• Pass full table primary keys to the merge factory; retain trimmed keys for physical keys and sorting.
• Keep realtime Noop compaction unchanged.
• Preserve non-realtime merge/read behavior; the merge-factory change is limited to the realtime creation call.

Known Issues

This PR aligns realtime partial-update merging with the existing ordinary Writer behavior by reusing the same merge functions. It does not fix the existing staged-merge defects or change non-realtime merge/read behavior. The ordinary Writer reproductions are tracked separately in #524 and will be addressed independently. Realtime may inherit these limitations; this PR does not establish correctness for all affected combinations.

Tests

Previously completed validation for feature commit 2e2f194ccdab76831b2988a9b749f5d8c299d8f7: 9 realtime integration tests and 20 core tests passed (29 total). These tests were not rerun when publishing this PR.

The four new integration tests are:

• RealtimeWriteInteTest.TestPkPartialUpdateDeleteAcrossCommits
• RealtimeWriteInteTest.TestPkPartialUpdateSequenceGroups
• RealtimeWriteInteTest.TestPkPartialUpdateAggregationSpillAndRecovery
• RealtimeWriteInteTest.TestPkPartialUpdatePartitionedDefaultAggregationRetract

The other five integration tests cover existing primary-key reads, recovery, writer handoff, and multiple batches. Core coverage includes KeyValueFileStoreWriteTest.* and FileStoreWriteTest.*.

Coverage exercises real memory queries, prepare/commit and normal disk reads, spill, reopen, and replay. This is focused validation, not exhaustive partial-update semantics, full CI, Java interoperability, or all repository tests.

API and Format

No public include/paimon/ API, storage format, or protocol changes.

Documentation

Updated the realtime user guide to document partial-update support and its scope.

Generative AI tooling

Generated-by: OpenAI Codex (CLI 0.160.0)

[lxy-9602]

With partial-update and DVs enabled, pushing value predicates into high-level disk files can discard rows needed to complete an in-memory partial update.

For example:

Disk (after compaction): (id=1, a="old", b="keep")
Memory partial update:  (id=1, a="new", b=null)
Query: WHERE a = 'new'

Expected: (id=1, a="new", b="keep")
Actual:   (id=1, a="new", b=null)

The disk row is filtered out before merging, so b="keep" is lost.

Please either push down only primary-key predicates across all disk levels and evaluate value predicates after merging, or reject the combination of realtime partial-update and DVs for now.