缓存旁路工作流
patterns
缓存旁路模式，包括缓存查找、缓存未命中时的数据库回退、缓存填充、基于TTL的过期和直写失效。
完整 FlowZap 代码
Application { # Application
n1: circle label:"Start"
n2: rectangle label:"Request data by key"
n3: rectangle label:"Return data to caller"
n4: circle label:"End"
n1.handle(right) -> n2.handle(left)
n2.handle(bottom) -> CacheLayer.n5.handle(top) [label="Lookup"]
n3.handle(right) -> n4.handle(left)
}
CacheLayer { # Cache Layer
n5: rectangle label:"Check cache for key"
n6: diamond label:"Cache hit?"
n7: rectangle label:"Return cached value"
n8: rectangle label:"Query database"
n9: rectangle label:"Store in cache with TTL"
n5.handle(right) -> n6.handle(left)
n6.handle(right) -> n7.handle(left) [label="Yes"]
n6.handle(bottom) -> n8.handle(top) [label="No"]
n7.handle(top) -> Application.n3.handle(bottom) [label="From cache"]
n8.handle(bottom) -> Database.n10.handle(top) [label="Fetch"]
n9.handle(top) -> Application.n3.handle(bottom) [label="From DB"]
}
Database { # Database
n10: rectangle label:"Execute query"
n11: diamond label:"Data found?"
n12: rectangle label:"Return result set"
n13: rectangle label:"Return empty result"
n10.handle(right) -> n11.handle(left)
n11.handle(right) -> n12.handle(left) [label="Yes"]
n11.handle(bottom) -> n13.handle(top) [label="No"]
n12.handle(top) -> CacheLayer.n9.handle(bottom) [label="Populate cache"]
n13.handle(top) -> Application.n3.handle(bottom) [label="Not found"]
}
WriteOperation { # Write Operation
n14: rectangle label:"Update database"
n15: rectangle label:"Invalidate cache key"
n16: diamond label:"Write-through?"
n17: rectangle label:"Update cache directly"
n18: rectangle label:"Let cache expire"
n14.handle(right) -> n15.handle(left)
n15.handle(right) -> n16.handle(left)
n16.handle(right) -> n17.handle(left) [label="Yes"]
n16.handle(bottom) -> n18.handle(top) [label="No"]
n17.handle(top) -> Application.n3.handle(bottom) [label="Updated"]
n18.handle(top) -> Application.n3.handle(bottom) [label="Invalidated"]
}