[r2dbc] getRowsUpdated() returns 0 for successful INSERT…SELECT — needs reliable written_rows

ClickHouseResult から始め、ClickHouseResponseSummary.getProgress()、getStatistics()、およびトップレベルの getWrittenRows() がどのように UpdateCount を提供しているかを追跡します。HTTP トランスポートを使用して INSERT INTO … SELECT クエリを再現し、getRowsUpdated() と最終的な written_rows の値を比較します。選択した完了後の権威ある値が確実に公開され、成功する INSERT…SELECT に対するリグレッションカバレッジがあることをもって完了とします。

Summary

ClickHouseResult.getRowsUpdated() in clickhouse-r2dbc returns 0 for
successful INSERT INTO … SELECT FROM … queries that did write rows. This
makes it impossible to reliably distinguish "INSERT…SELECT wrote 0 rows
because the SELECT produced none" from "INSERT…SELECT wrote N rows but the
driver reported 0" at the application layer.

The same row count appears correctly in system.query_log.written_rows
server-side, and the HTTP X-ClickHouse-Summary header also carries an
accurate written_rows once the query finishes. The information exists; the
driver just doesn't expose it via the standard R2DBC Result.getRowsUpdated()
contract for this query shape.

Reproduction

• Driver: com.clickhouse:clickhouse-r2dbc:0.9.0 (also reproduces on 0.8.x)
• Server: ClickHouse 25.3
• Query shape: INSERT INTO target_table (...) SELECT ... FROM source_table WHERE ...
• Connection settings: async_insert=1, wait_for_async_insert=1
  (per docs, async_insert is a no-op for INSERT…SELECT, but we set it
  globally for the INSERT VALUES path on the same connection)

Flux.from(statement.execute())
    .flatMap(Result::getRowsUpdated)   // emits 0 even when N rows were inserted
    .reduce(0L, Long::sum)
    // observed: returns 0

Verifying server-side after the query finishes:

SELECT written_rows
FROM system.query_log
WHERE query_id = '...' AND type = 'QueryFinish';
-- returns N (the correct count)

Root cause

Looking at ClickHouseResult constructor (current main):

Mono<? extends UpdateCount> updatedCount = Mono.just(response)
    .map(ClickHouseResponse::getSummary)
    .map(ClickHouseResponseSummary::getProgress)
    .map(ClickHouseResponseSummary.Progress::getWrittenRows)
    .map(UpdateCount::new);

The driver reads written_rows from Summary.getProgress(), which is the
interim progress event snapshot — not the final summary. For
INSERT…SELECT queries, a definitive post-completion written_rows is
typically reflected in Summary.getStatistics() (or in a final progress
event that doesn't always land before the subscriber observes completion).

ClickHouseResponseSummary exposes both getProgress() and getStatistics(),
and the top-level getWrittenRows() delegates to progress.

Use case

Detecting at the application layer when an INSERT…SELECT wrote zero rows
(to surface inconsistency conditions before committing dependent state).
Since getRowsUpdated() can return 0 even on success, the check fires
false positives.

Asks

Any one of the following would unblock us:

1. Source getRowsUpdated() from Summary.getStatistics() (or whichever
   field is authoritative post-completion) instead of from Summary.getProgress().
2. Expose the raw ClickHouseResponseSummary from ClickHouseResult (or a
   similar handle), so callers can read the final fields themselves.
3. Document the current semantics so applications know not to rely on
   getRowsUpdated() for INSERT…SELECT.

Happy to send a PR for (1) or (2) — please confirm which direction you'd
prefer.

Environment

• clickhouse-r2dbc: 0.9.0
• clickhouse-client / clickhouse-http-client: 0.9.0
• ClickHouse server: 25.3.x
• Connection: HTTP transport