> For the complete documentation index, see [llms.txt](https://liuzhenglaichn.gitbook.io/system-design/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://liuzhenglaichn.gitbook.io/system-design/basics/cache.md). # Cache Increase the performance of **read** operations. Application server cache: local cache. Example: map, leveldb. High performance but hard to scale. Violates stateless server principle. CDN: static content cache, media/binarries ## Independent cache system * **Redis**: complex data structure. Built-in high availability * **Memcache**: simple key-value, high concurrency ## Cache writing policy write-through: write to cache and db. write-around: discard cache result, write db write-back: only write cache, don't write to DB. not consistent. If the cache content is easy to calculate, use write-through, otherwise, write-around. Cache eviction policies: LRU, LFU, FIFO. ## What to Cache TODO ## Cache Eviction Strategy TODO --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://liuzhenglaichn.gitbook.io/system-design/basics/cache.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.