- The Storage Manager is the glue between client and server sides. Every object saved in the cache is allocated a StoreEntry structure. While the object is being accessed, it also has a MemObject structure.
- Squid can quickly locate cached objects because it keeps (in memory) a hash table of all StoreEntry's. The keys for the hash table are MD5 checksums of the objects URI. In addition there is also a storage policy such as LRU that keeps track of the objects and determines the removal order when space needs to be reclaimed. For the LRU policy this is implemented as a doubly linked list.
- For each object the StoreEntry maps to a cache_dir and location via sdirn and sfilen. For the "ufs" store this file number (sfilen) is converted to a disk pathname by a simple modulo of L2 and L1, but other storage drivers may map sfilen in other ways. A cache swap file consists of two parts: the cache metadata, and the object data. Note the object data includes the full HTTP reply—headers and body. The HTTP reply headers are not the same as the cache metadata.
- Client-side requests register themselves with a StoreEntry to be notified when new data arrives. Multiple clients may receive data via a single StoreEntry. For POST and PUT request, this process works in reverse. Server-side functions are notified when additional data is read from the client.
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