wangyong9999 opened a new pull request, #282:
URL: https://github.com/apache/paimon-cpp/pull/282
### Purpose
Linked issue: none
`ScanContextBuilder::Impl` eagerly calls `CreateDefaultExecutor()` twice per
builder
lifetime: once in the member initializer and once more in `Reset()`, which
`Finish()`
invokes right after building the context. Each call constructs a
`DefaultExecutor`
that spawns `DEFAULT_EXECUTOR_THREAD_COUNT` (4) worker threads and joins
them on
destruction, so every `ScanContextBuilder` costs eight thread creations even
when the
caller supplies its own executor through `WithExecutor()`.
Point-lookup style serving code builds one `ScanContextBuilder` per key.
Measured with
`strace -f -c -e trace=clone` on such a path, each lookup performed about
nine `clone`
calls and eight of them came from this builder.
This change resolves the executor lazily in `Finish()`:
- `executor_` defaults to null and `Reset()` only clears it.
- `Finish()` uses the explicitly set executor, otherwise
`GetGlobalDefaultExecutor()`,
so `ScanContext::GetExecutor()` stays non-null and the null check in
`TableScan`
is unaffected.
`ReadContextBuilder` already creates its default executor lazily in
`Finish()`, so this
brings the two builders in line.
### Tests
- `ScanContextTest.TestDefaultExecutorIsGlobalSingleton` (new): contexts
built without
`WithExecutor()` share the process wide default executor, and an executor
set on a
builder only applies to the `Finish()` that follows it.
- Existing `ScanContextTest.*` cases pass locally with `paimon-core-test`.
### API and Format
No public API or storage format change. Callers that relied on a context
built without
`WithExecutor()` owning a private 4-thread executor now share the global
default
executor instead.
### Documentation
No.
### Generative AI tooling
Generated-by: Claude Code (Claude Fable 5.1)
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