feat(native): Add config for asyc cache numShards

[kewang1024]

== NO RELEASE NOTE ==

Summary by Sourcery

Add configurable shard count for the async data cache and wire it through server initialization.

New Features:

• Introduce a new system config option to control the number of async cache shards with a default value.
• Expose the async cache shard count to the async data cache options during server initialization.

Tests:

• Add unit tests covering default and custom values for the async cache shard count system config.

[sourcery-ai]

Reviewer's Guide

Introduce a new configuration property async-cache-num-shards to control the number of shards used by the async data cache, plumb it through SystemConfig with a default of 4, and pass it into AsyncDataCache options along with unit tests for the default and override behavior.

Sequence diagram for passing async cache numShards into AsyncDataCache

sequenceDiagram
    actor Admin
    participant SystemConfig
    participant PrestoServer
    participant AsyncDataCache

    Admin->>SystemConfig: Set async-cache-num-shards (optional)
    Admin->>PrestoServer: Start server
    PrestoServer->>SystemConfig: asyncCacheMaxSsdWriteRatio()
    SystemConfig-->>PrestoServer: maxSsdWriteRatio
    PrestoServer->>SystemConfig: asyncCacheSsdSavableRatio()
    SystemConfig-->>PrestoServer: ssdSavableRatio
    PrestoServer->>SystemConfig: asyncCacheMinSsdSavableBytes()
    SystemConfig-->>PrestoServer: minSsdSavableBytes
    PrestoServer->>SystemConfig: asyncCacheNumShards()
    SystemConfig-->>PrestoServer: numShards (default 4 or overridden)
    PrestoServer->>AsyncDataCache: create(allocator, ssd, Options{maxSsdWriteRatio, ssdSavableRatio, minSsdSavableBytes, numShards})
    AsyncDataCache-->>PrestoServer: cache_instance_with_shards

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Class diagram for new async cache numShards configuration

classDiagram
    class ConfigBase

    class SystemConfig {
      <<Config>>
      +static constexpr string_view kAsyncCacheNumShards
      +int32_t asyncCacheMinSsdSavableBytes() const
      +int32_t asyncCacheNumShards() const
      +std_chrono_duration_double asyncCachePersistenceInterval() const
      +bool asyncCacheSsdDisableFileCow() const
    }

    class PrestoServer {
      +void initializeVeloxMemory()
      -shared_ptr_AsyncDataCache cache_
    }

    class AsyncDataCacheOptions {
      +double maxSsdWriteRatio
      +double ssdSavableRatio
      +int32_t minSsdSavableBytes
      +int32_t numShards
    }

    class AsyncDataCache {
      +static shared_ptr_AsyncDataCache create(Allocator allocator, unique_ptr_SsdCache ssd, AsyncDataCacheOptions options)
    }

    ConfigBase <|-- SystemConfig
    PrestoServer ..> SystemConfig : reads_config
    PrestoServer ..> AsyncDataCacheOptions : constructs
    PrestoServer ..> AsyncDataCache : create_with_numShards
    AsyncDataCacheOptions ..> AsyncDataCache : used_to_configure

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File-Level Changes

Change	Details	Files
Add async-cache-num-shards as a new system configuration option with default and accessor	Declare new async-cache-num-shards key and documentation comment in the system configuration header Register async-cache-num-shards in the SystemConfig constructor with a numeric default value of 4 Expose an asyncCacheNumShards() getter that reads the optional integer property	presto-native-execution/presto_cpp/main/common/Configs.h presto-native-execution/presto_cpp/main/common/Configs.cpp
Wire async-cache-num-shards into PrestoServer async cache initialization	Extend AsyncDataCache::Options construction to include asyncCacheNumShards from SystemConfig when creating the cache	presto-native-execution/presto_cpp/main/PrestoServer.cpp
Add unit test coverage for async-cache-num-shards config behavior	Add a new ConfigTest case validating the default asyncCacheNumShards value and an overridden value via configuration initialization	presto-native-execution/presto_cpp/main/common/tests/ConfigTest.cpp

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[sourcery-ai]

Hey - I've left some high level feedback:

• Given the comment that async-cache-num-shards "must be a power of 2", consider adding explicit validation (and a clear error message) when reading this config to guard against non-power-of-two or non-positive values rather than silently accepting bad input.
• It may be worth clarifying in the new test (or via an additional one) how the system behaves when async-cache-num-shards is set to an invalid value (e.g., 0 or negative), to ensure the contract around this config is well-defined and enforced.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Given the comment that `async-cache-num-shards` "must be a power of 2", consider adding explicit validation (and a clear error message) when reading this config to guard against non-power-of-two or non-positive values rather than silently accepting bad input.
- It may be worth clarifying in the new test (or via an additional one) how the system behaves when `async-cache-num-shards` is set to an invalid value (e.g., 0 or negative), to ensure the contract around this config is well-defined and enforced.

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[steveburnett]

Please include documentation for the new property, as described in Designing Your Code in CONTRIBUTING.md:

"All new language features, new functions, session and config properties, and major features have documentation added"

[xiaoxmeng]

@kewang1024 thanks!