[Feature] Improve scan performance in hot read paths

首先，对并发扫描路径中 manifest reader 的 StructArray::fields() 调用和 Avro decoder 的 ArrayBuilder::type() 调用进行性能分析。确定适用于不可变 Arrow 元数据的 batch、reader 或 builder 生命周期，然后验证在相应的 Arrow 对象树被替换时缓存会失效。完成的标准是，在并发扫描期间降低 shared-pointer 同步和引用计数的开销。

Search before asking

• I searched in the issues and found nothing similar.

Motivation

Recent profiling of highly concurrent scans has revealed several performance bottlenecks caused by
repeated operations on Arrow-returned shared_ptr objects in hot read loops.

Two significant cases have been identified:

1. Manifest readers repeatedly call StructArray::fields() while processing individual rows. This
   copies shared_ptr<Array> objects and, with GCC 8.3's libstdc++, can introduce substantial lock
   contention through _Sp_locker, pthread_mutex_lock, and futex waits when multiple workers read
   manifests concurrently.

2. Avro decoding calls ArrayBuilder::type() for every integer and timestamp value. Because this
   method returns std::shared_ptr<DataType> by value, concurrent scans repeatedly modify reference
   counts on shared Arrow primitive data types, causing cache-line contention. Profiling showed
   ArrayBuilder::type() and shared-pointer release operations accounting for a large proportion of
   samples after the manifest bottleneck was removed.

This issue tracks the broader effort to identify and eliminate similar shared-pointer operations
from scan hot paths. The goal is to cache immutable Arrow metadata at an appropriate batch, reader,
or builder lifetime, while ensuring caches are invalidated whenever the corresponding Arrow object
tree is replaced.

The expected outcome is lower synchronization and reference-counting overhead under concurrent
scans, allowing CPU time to return to actual decoding, memory copying, and buffer management.

Solution

No response

Anything else?

No response

Are you willing to submit a PR?

• I'm willing to submit a PR!