Trait L2CacheBackend 

pub trait L2CacheBackend: Send + Sync {
    // Required methods
    fn get<'a>(
        &'a self,
        key: &'a str,
    ) -> Pin<Box<dyn Future<Output = Result<Option<Vec<u8>>, CacheError>> + Send + 'a>>;
    fn set<'a>(
        &'a self,
        key: &'a str,
        value: &'a [u8],
        ttl: Option<Duration>,
    ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>;
    fn delete<'a>(
        &'a self,
        key: &'a str,
    ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>;
    fn invalidate_prefix<'a>(
        &'a self,
        prefix: &'a str,
    ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>;
}

L2 缓存后端 trait（分布式抽象）

定义跨进程共享的二级缓存后端接口，支持进程内内存、Redis 等实现。 手动解糖 async 方法（不使用 #[async_trait]），与 Connection trait 风格一致。

设计要点

• 键值以 &[u8] 传输：后端无关的序列化格式（由调用方决定 bincode/json 等）
• TTL 可选：Some(Duration) 设置过期时间，None 表示永不过期
• 前缀失效：invalidate_prefix 批量失效某前缀的所有键（用于表级失效）

实现方

• InMemoryBackend：进程内内存后端（默认，单机场景）
• RedisBackend：Redis 分布式后端（stub，需启用 redis feature 并补充依赖）

Required Methods

fn get<'a>( &'a self, key: &'a str, ) -> Pin<Box<dyn Future<Output = Result<Option<Vec<u8>>, CacheError>> + Send + 'a>>

获取缓存值，不存在或已过期返回 None

fn set<'a>( &'a self, key: &'a str, value: &'a [u8], ttl: Option<Duration>, ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>

设置缓存值，ttl 为 None 表示永不过期

fn delete<'a>( &'a self, key: &'a str, ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>

删除单个缓存键

fn invalidate_prefix<'a>( &'a self, prefix: &'a str, ) -> Pin<Box<dyn Future<Output = Result<(), CacheError>> + Send + 'a>>

按前缀批量失效缓存项（用于表级失效）

Dyn Compatibility

This trait is dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors

impl L2CacheBackend for InMemoryBackend

impl L2CacheBackend for RedisBackend

Available on non-crate feature redis only.