SemanticCache.check() unconditionally refreshes TTL on hit (sliding-window with no opt-out)

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@omribz156 已经在做这个了。

开始于 2026年5月25日。

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Issue 类型
功能
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技术栈
python, redis
领域
backend-api-design, databases

调研方向

从 redisvl/extensions/cache/llm/semantic.py 中 SemanticCache.check() 的第 432 行附近开始，然后阅读周围的 SemanticCache 构造函数以及当前的 TTL 刷新路径。验证所提议的构造函数标志和每次调用的覆盖选项在禁用时仍保持默认行为并允许纯读取；当两种选项都得到支持且不改变现有调用方时，即表示完成。

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描述

cache enhancement

Current behavior

SemanticCache.check (redisvl/extensions/cache/llm/semantic.py:432) refreshes the TTL of every matched entry on every hit:

# Refresh TTL on all found keys
for key in redis_keys:
    self.expire(key)

This is a sliding-window TTL: a popular entry effectively lives as long as it keeps getting hit. There is no constructor flag, per-call argument, or per-entry attribute to disable this.

Why this is a problem

Sliding window is the wrong default in any domain where the popularity of an entry correlates with the cost of it being stale:

  • a procedure superseded by a regulatory bulletin that the cache has not yet invalidated
  • a balance-patch-affected gameplay answer in a live-ops surface
  • a pricing or eligibility answer that changed at midnight

In these domains the most-asked question is the most likely to be cached and the most likely to fan out a stale answer. The standard mitigation today — store an absolute expires_at numeric and filter on it at read time — works but requires every customer to discover the pattern independently.

Proposed API

SemanticCache(
    name="cache",
    redis_url=...,
    refresh_ttl_on_hit=True,    # current behavior, default unchanged
)

cache.check(
    prompt=...,
    refresh_ttl=None,           # per-call override
)

refresh_ttl_on_hit=False would make check() a pure read. Customers wanting absolute expiry would set this to False, store a numeric expires_at filterable field, and filter on it.

Backwards compatibility

Default remains True. Existing behavior unchanged. Opt-in behavioral change for customers who need it.

Notes

Surfaced while writing a scoped semantic caching architecture spec; came up repeatedly when stress-testing the design against regulated and fast-mutating domains where sliding-window TTL is actively hostile.

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