Re: A youtube and windows update cache thing.

>>
>> Hi,
>> just a basic question, relevant to squid2.7, at least:
>>
>> AFAIK, without looking into the src code, squid2.7 requests and caches
>> the complete object, before delivering the data to fulfill the first
>> range request.
>> Delivery might even start as soon as the data for the actual range
>> request is available.
>>
>> Further range requests will be handled from the cached "complete object".
>>
>> In case, this is correct, then it should also be valid using
>> storeurl_rewrite_program in squi2.7
>>
>> The probability, that other parts of the cached "complete object" will be reuested, is
>> quite high, so no
>> no need for something new.
>>
>> This strategy might even be an advantage, in case, the range requests
>> for the same object vary in size, which might be dependent upon
>> connection speed.
>>
> Hey,
> As far as I know squid serves 206 partial responses from cache only if the full object exists in cache.

I can not follow the flow of execution in squid2.7, but I am not shure, that you are correct.
These excerpts from squi2.7 MIGHT indicate, that transmission of
data for a range request to the client can start before the complete object is cached:

squid.conf:

# TAG: range_offset_limit (bytes)
# Sets a upper limit on how far into the the file a Range request
# may be to cause Squid to prefetch the whole file. If beyond this
# limit Squid forwards the Range request as it is and the result
# is NOT cached.
#
# This is to stop a far ahead range request (lets say start at 17MB)
# from making Squid fetch the whole object up to that point before <=============================
# sending anything to the client.

client_side.c:
clientCheckRangeForceMiss(StoreEntry * entry, HttpHdrRange * range)
{
     /*
      * If the range_offset_limit is NOT in effect, there
      * is no reason to force a miss.
      */
     if (0 == httpHdrRangeOffsetLimit(range))
        return 0;
     /*
      * Here, we know it's possibly a hit. If we already have the
      * whole object cached, we won't force a miss.
      */
     if (STORE_OK == entry->store_status)
        return 0; /* we have the whole object */
     /*
      * Now we have a hit on a PENDING object. We need to see <===========================================
      * if the part we want is already cached. If so, we don't
      * force a miss.
      */
     assert(NULL != entry->mem_obj);
     if (httpHdrRangeFirstOffset(range) <= entry->mem_obj->inmem_hi)
        return 0;
     /*
      * Even though we have a PENDING copy of the object, we
      * don't want to wait to reach the first range offset,
      * so we force a miss for a new range request to the
      * origin.
      */
     return 1;
}

I guess, Alex should have a definite answer.

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