[Swift-devel] discussion for swift output file path

[Zhao Zhang]

Mihael Hategan wrote:
> On Fri, 2008-11-07 at 01:07 +0000, Ben Clifford wrote:
>   
>> On Thu, 6 Nov 2008, Mihael Hategan wrote:
>>
>>     
>>> It may also make sense to coalesce all the trees into one, such that
>>> data, info, and temporary job dirs are created in the same directory
>>> (e.g. (info/a/0, job/a/0) becomes (a/0/info, a/0/job)), since it will
>>> reduce the overall number of operations.
>>>       
>> Perhaps does for info and job where the access/lock patterns are the same 
>> under both the info and job tree.
>>
>> But the shared data tree needs to be hashed by something based on the file 
>> (eg a hash of the filename) rather than on something specific to a 
>> particular job.
>>
>> Putting the shared directories under the same hash tree as info/ and job/ 
>> would reduce the number of directories in total but would increase lock 
>> contention on those directories, because cached data file accesses follow 
>> a different pattern from info/ and job/ accesses.
>>     
>
> Only if we assume non-reentrant read locks. And this would need some
> investigation, but if concurrent reads do not create contention, then
> there is no problem, because once a job is done, there is no more
> writing to its directory.
>
>   
well, as far as we know, the concurrent reads do not create contention.

zhao