On 07/12/2017 10:11 AM, Amos Jeffries wrote: > On 12/07/17 22:31, bugreporter wrote: >> Hi, >> >> Can anybody help me to confirm my understanding of the memory usage vs >> the >> persistent cache capacity? Below my understanding: >> >> According to http://wiki.squid-cache.org/SquidFaq/SquidMemory: >> >> 1- We need 14 MB of memory per 1 GB on disk for 64-bit Squid.The wiki is >> there since I know squid (ie. i'm very old now). Is this information >> still >> valid? > > Yes. It is a rough estimate based on the size of code objects used to > store each request message - they have not changed in at least the past > 10 years. For the record, the StoreEntry object has changed, but I do not know how much those (minor!) changes affect the rough estimate. It is likely that they do not. >> 2- Is this assumption based on the default value of 13 KB for >> *store_avg_object_size*? > > No. Actually, the answer is probably "yes" or "yes, that or a similar mean object size value". > That avg object size is for the full object with payload. ... which is used to estimate how many cache_dir index entries Squid will need to create for a cache_dir of a given size. > The 10 or 14 MB is purely for the metadata necessary to index those > cached objects. Which is the HTTP message header text plus a bunch of > Squid code objects. HTTP headers are not a part of the in-memory cache_dir index. StoreEntry and LruNode (or equivalent) are pretty much the only structures we place in the cache_dir index. A "bunch of Squid code objects" are not created for that index (but get created during a cache hit and may remain in RAM for some time after that). > To get the metadata size add the per-object sizes (first number column) > of HttpReply + MemObject + HttpHeaderEntry + all objects whose name > starts with HttpHdr* + StoreEntry + all objects whose name starts with > StoreMeta*. AFAICT, StoreEntry and LruNode (or equivalent) are the only structures created for the cache_dir index. All other structures are not relevant in that scope. > Though nowdays the 2^27 objects per cache_dir limitation is proving to > be far more restrictive than the RAM index size. Agreed, but YMMV. > So depending on your > "Mean Object Size" you may find yourself limited to only using 100 GB or > less of a TB HDD. ... unless you use multiple cache_dirs per HDD. Alex. _______________________________________________ squid-users mailing list squid-users@xxxxxxxxxxxxxxxxxxxxx http://lists.squid-cache.org/listinfo/squid-users
