[Feature] Improve scan performance in hot read paths

Inizia profilando le chiamate a StructArray::fields() del manifest reader e le chiamate a ArrayBuilder::type() dell’Avro decoder nei percorsi di scansione concorrenti. Individua la durata di vita appropriata del batch, reader o builder per i metadati Arrow immutabili, quindi verifica che le cache vengano invalidate quando il corrispondente albero di oggetti Arrow viene sostituito. Il lavoro è completato quando vengono ridotti l’overhead di sincronizzazione degli shared pointer e quello del conteggio dei riferimenti durante le scansioni concorrenti.

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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

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Anything else?

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Are you willing to submit a PR?

• I'm willing to submit a PR!