linliu-code opened a new pull request, #672:
URL: https://github.com/apache/hudi-rs/pull/672
**Stacked on #639–#671** — review only the last commit. **Merge-on-read
reader only; the existing reader is untouched.**
## The bug
A table from version 9 on records how it merges in
`hoodie.record.merge.mode`. Older ones do not, and this reader guessed — from
`hoodie.table.record.merge.strategy`, a key **no Hudi table writes** (zero
occurrences across every fixture). It always fell through to a derivation that
returns `append_only` whenever meta fields are off or no ordering field is set.
`append_only` has no merge-mode counterpart, so the read was **refused**.
## What Hudi does
`HoodieTableConfig.inferMergingConfigsForPreV9Table` — three inputs, in
precedence order:
```
payload class or strategy id set?
DefaultHoodieRecordPayload | EventTimeAvroPayload → EVENT_TIME_ORDERING
OverwriteWithLatestAvroPayload → COMMIT_TIME_ORDERING
strategy eeb8d96f-… → EVENT_TIME ce9acb64-… → COMMIT_TIME
anything else → CUSTOM
(v8+: strategy id wins; before: payload class wins)
otherwise
ordering field set ? EVENT_TIME_ORDERING : COMMIT_TIME_ORDERING
```
**The inputs were always present.** The strategy ids in our fixtures match
Hudi's constants exactly (`eeb8d96f-…`, `ce9acb64-…`, and the payload-based
sentinel `00000000-…`), and 37 fixtures carry a payload class. This reader
consulted none of them.
I confirmed the same rule is what the engine integration applies: gluten's
`Hudi1xMergeConfigResolver.resolveMergeConfigs` delegates straight to
`inferMergingConfigsForPreV9Table`, gated on `tableVersion < NINE` — which is
why a v9 table passes through untouched.
## Two consequences worth naming
**Tables that were refused now read.** `v6_empty` and
`v6_simplekeygen_hivestyle_no_metafields` are the fixtures that hit the old
fallback; both now merge by commit time.
**A v6 `OverwriteWithLatestAvroPayload` table now merges by commit time, not
event time.** Its payload class says so, and it outranks the ordering-field
guess. That is a semantics change for those tables — and the correct one:
"overwrite with latest" means latest by commit, not by ordering field.
## Why `CUSTOM` is still refused
A table with a merger of its own is rejected rather than merged as if it had
none.
Gluten *does* remap one case — a Debezium payload becomes
`EVENT_TIME_ORDERING` so it can offload — **but only after injecting the delete
marker and, for MySQL, substituting the ordering field with the composite
`(_event_bin_file, _event_pos)` this reader can actually compare.** Those
configs are not persisted on the table. Inferring the same remap here would
read such a table without them and drop its deletes silently.
An engine that has done that work says so by setting
`hoodie.record.merge.mode` outright, which is read before any inference. That
is the right seam.
## Scope
**The existing reader is untouched**, per the constraint on this change. It
still derives its own strategy, so the two readers now disagree on these tables
— the merge-on-read one being correct. A differential comparison between them
still has to wait for the legacy path to be brought across.
## Tests
An 11-case matrix mirroring the cases Java's own inference is tested
against: the ordering-field fallback both ways, each built-in payload class,
each built-in strategy id, the payload-based sentinel, and the version-8
tie-break in both directions.
Plus: a real fixture that was refused before and now resolves to commit-time
ordering, and a table with its own merger still refused with a reason.
The two tests that asserted the old behavior are replaced — they encoded the
bug.
Full workspace green: 1208 lib + 79 table-read + 39 datafusion + 21 + 12.
Clippy clean in the changed file.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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