[Pvfs2-developers] concurrent ls and rm

[Phil Carns]

> 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.

I just replicated this using just 1000 files (each about 200 bytes) in a 
single directory, again with one client doing an rm -rf and another 
client doing an ls in the same directory.

Unfortunately, it doesn't look like disabling the pcache made any 
difference.  I first tried disabling it by adding a "return 0" at the 
top of the PINT_dbpf_keyval_pcache_insert() function.  I also tried 
modifying the dbpf_keyval_iterate_skip_to_position() function to not 
call PINT_dbpf_keyval_pcache_lookup().

Is there anything else I could do to make sure the pcache isn't being 
used, or does this indicate that the problem is elsewhere?

-Phil