Re: Caching responses with "Vary" responses

On 19/07/2012 9:50 p.m., Alexander Komyagin wrote:
> On Wed, 2012-07-18 at 11:10 -0600, Alex Rousskov wrote:
>> On 07/17/2012 09:28 AM, Alexander Komyagin wrote:

>>> It seems that on the first HIT we have successfully loaded data from the
>>> swap store, but then we save the data to shared memory. So the next
>>> request takes data from shm. And it looks like Squid doesn't save
>>> mem_obj->vary_headers to shm!!
>> Shared memory cache is meant to be just like a disk cache in this
>> aspect. It does not know anything about mem_obj->vary_headers and just
>> packs/unpacks the STORE_META_STD TLV (see StoreMapSlot
>> src/ipc/StoreMap.h) part of StoreEntry.
>>
>> I do not see vary_headers used by any src/fs/* code. Do you know how the
>> disk cache gets them? Perhaps there is a higher level call to pack and
>> unpack Vary request headers that the MemStore is missing. We can add
>> special field/code to StoreMapSlot but I would prefer to see how it is
>> done for the disk storage first, in hope that we can reuse the same code.
>>
> For the disc cache, STORE_META_VARY_HEADERS is used (see
> store_swapmeta.cc). Appropriate tlv is added to the list.
>
> But for shm I don't see any SwapMeta work! There are some calls that are
> writing reply headers and body to the internal mem_hdr object and then I
> can see this object data copied to shm!
>
> In the meantime, those who are in need can use my small dirty hack
> (squidv3-vary-headers-shm-hack.patch) that packs mem_obj->vary_headers
> as an additional reply header, so it can be flawlessly saved to shm and
> recovered afterwards.

Isn't vary_headers just a copy of Vary: reply header anyway? so it is
already in the response headers once.

Amos
Received on Fri Jul 20 2012 - 02:46:51 MDT