Squid uses this value as a hint for estimating the size of certain data structures. In particular, Squid calculates an estimate for the total number of objects in the cache, based on this value and the sum of all cache_dir sizes. This estimate is, in turn, used to calculate the number of hash buckets for the primary index to cached objects. Additionally, it can estimate the cache digest size, if that feature is enabled.
In most cases the default should be sufficient. You can find the actual value for your cache by querying the cache manager. Look for “Mean Object Size” on the info page (see Section 126.96.36.199).
store_avg_object_size 13 KB
store_avg_object_size 10 KB
cache_dir, digest_bits_per_entry, store_objects_per_bucket