[Pvfs2-developers] concurrent ls and rm

[Rob Ross]

hmm. ok. stupid readdir. i think i've fought passing the name for a long 
time, but i'm ready to give in.

rob

Sam Lang wrote:
> 
> On Sep 5, 2007, at 10:47 AM, Rob Ross wrote:
> 
>> Are those cookies not somehow tied to a particular client?
> 
> No they're not.
> -sam
> 
>>
>> Sam Lang wrote:
>>> On Sep 5, 2007, at 10:31 AM, Phil Carns wrote:
>>>> We have run into a problem with running "rm -rf" and "ls" 
>>>> concurrently on the same directory from different client nodes.  In 
>>>> the particular case that we are looking at, the directory has about 
>>>> 7000 files in it but no subdirectories.  If we do an ls on the 
>>>> directory while an "rm -rf" is running from a different client, then 
>>>> the rm fails to remove all of the files.  It seems to get worse if 
>>>> you do more than one ls while the rm is working.  This is on RHEL4 
>>>> with 2.6.9.something kernels.
>>>>
>>>> Has anyone else seen this?  Any idea what the problem is?
>>> Hi Phil,
>>> The trove layer caches the position -> name mapping for positions it 
>>> returns back to the client on a readdir.  The problem is probably 
>>> related to caching those entries, where the readdir for the rm is 
>>> iterating over the directory, and so inserting position -> name 
>>> entries into the cache, and then ls is coming along and replacing 
>>> those entries with its own, where the position is the same but the 
>>> name is further down in the directory (because rm has removed some of 
>>> them).  That's just a guess though.  You could see if disabling that 
>>> position cache helps fix the problem, disabling it will cause the 
>>> berkeley db iterate to walk through all the entries up to the 
>>> position though, so its going to be much slower.  The position cache 
>>> is in dbpf-keyval-pcache.c.
>>> Probably the right long term solution is to return the name as the 
>>> position, instead of an int.
>>> -sam
>>>>
>>>> thanks,
>>>> -Phil
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>