Squid internals

The Storage Manager (src/store*.c)
Private objects
A private StoreEntry is an object which shouldn't be used by any other clients besides the one which created it. For example, errors, POSTs, non-cacheable replies, and are destroyed after the client closes

Public objects
A public StoreEntry is an object which can be used by multiple clients simultaneously. It can be cachable, and generally hangs around after the last open client closes