Re: I had some troubles with all the changes lately, upgrade and other stuff. need help with this patch review

On 11/13/2012 10:20 AM, Eliezer Croitoru wrote:
> On 11/5/2012 9:28 PM, Eliezer Croitoru wrote:
>> On 11/5/2012 8:03 PM, Alex Rousskov wrote:
>>> On 11/05/2012 08:55 AM, Eliezer Croitoru wrote:
>>>
>>>> As I mentioned about the TCP_SWAP_FAIL_MISSS if someone can explain
>>>> literally or give an example of this kind of a case (outside of
>>>> store_url) and what should cause it?(I'm a bit confused about it).
>>>
>>> Does the following explanation help?
>>> http://www.squid-cache.org/mail-archive/squid-users/200104/0948.html
>>>
>>> As for a specific example, I can speculate that manually removing a ufs
>>> file corresponding to a cached entry should cause TCP_SWAP_FAIL_MISSS if
>>> that entry is later requested and found in store index (but not on
>>> disk).

>> Helped me to settle a bit with my speculations.
>> it's kind of weird since I can see that the file is there in the store
>> dir and can be accessed.

You asked for an example, and I found one. That particular example is a
good illustration of why a swap-in may fail, but it probably has little
or nothing to do with your specific problem.

>> From what was explained before the store index stores keys and not url,
>> am I right?

What is stored in a store index is kind of store-dependent so, ideally,
you should not care.

>> just throwing into the air, what are the steps when trying to find a
>> file in cache and serve it?

>> 1. predict the hash of the request.(if store_url present to use it)

Yes, "calculate the store key" based on request information may be a
more accurate description. This happens as a part of
Store::get()-related API discussed in item #2 below.

>> 2. lookup for the hash(get and head..) in the index?(memory? ufs? are
>> the same?)

Yes, see Store::get(), storeGetPublicByRequest(), and other related
storeGet*() and StoreEntry::get*() functions and methods. The Store
controller searches for the entry in various places, including memory
cache and disk caches.

>> 3. read the file mentioned in the index from disk? by what?
>> (I have seen some code but not sure if it's the point I should look at)

Yes, the cached entry is swapped in from disk or from memory. The
specific code depends on the store (memory, ufs, Rock, etc.). For
disk-related stores, it all starts in storeSwapInStart() IIRC.

HTH,

Alex.
Received on Tue Nov 13 2012 - 18:01:40 MST