[Gluster-devel] lookup caching

[Raghavendra G]

On Mon, Apr 12, 2010 at 1:26 PM, Olivier Le Cam <
Olivier.LeCam at crdp.ac-versailles.fr> wrote:

> Hello there,
>
>
> Raghavendra G wrote:
>
>>    I can see three protocol calls:
>>           - client_open()         (to both servers)            -
>> client_stat()         (to one server only: load balancing?)
>>           - client_flush()        (to both servers)
>>
>>
>> io-cache indeed sends open and flush to server. This is needed for correct
>> working of io-cache. As you've told below, since you are overriding lookup
>> call, stat is sent to server (stat and lookup are two different calls).
>>
>
> OK. So no easy workaround can get rid of that. Right?


you've to override stat also.


>
>
>  since lookup is being unwound if the stat is cached for an inode, you've
>> to also implement calls like unlink, rmdir (which deletes files/directories)
>> and flush the cache corresponding to the inode. Otherwise lookup will be
>> succeeding even for unlinked files, but the actual operations (like
>> open/chmod/chown etc) will fail.
>>
>
> I have added this yesterday afternoon, as well as some LOCK/UNLOCK in order
> to prevent concurrency problems. :)
>
>
>  You should also handle calls which can change the stat of a file or
>> directory (like write/chmod/chown). As a simple implementation you can just
>> flush the cache.
>>
>
> I did override setattr and fsetattr (for flushing the cache). Is it wrong?
> Do I have to override write/chmod/chown either?


You are right., chmod and chown are replaced by setattr. Sorry  about
that:). You need to flush the cache during write also. In general any fop
that can potentially change stat should be implemented.

>
>
>            if (cache->next) {
>>                   do {
>>                           cache = cache->next;
>>                           if (cache->ino == ino) {
>>
>>
>> instead of just returning, you can choose to update the cached stat with
>> the one passed as argument to this procedure.
>>
>>                                   return 0;       /* already in */
>>                           }
>>                   } while(cache->next);
>>           }
>>
>
> Thanks for suggestion.
>
> Best regards,
> --
> Olivier
>
>
>
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-- 
Raghavendra G
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