Les Mikesell wrote:
> Josh Rubin wrote:
>   
>> I hope this question isn't too dumb, but why does backuppc need to use
>> hard links?
>> Of course, nobody wants to change a widely used program in a way that
>> breaks everything,
>> so this is really a question about some new, future program.
>> Isn't the pool just a form of hash table that could be implemented lots
>> of ways?
>>     
>
> Creating a link is an atomic operation in the fileystem.  With anything 
> else you would have to add the overhead of some locking mechanism (with 
> the potential for deadlocks) to be sure that the equivalent to the link 
> and the count of them stayed in sync.   And, not too surprisingly it 
> turns out that filesystem operations are actually a pretty good way to 
> deal with storing files - it might not be impossible to do it better but 
> it wouldn't be easy.
>   

Locking mechanisms aren't always necessary. One of the advantages of 
hashed database systems, such as linear hash technology, is that 
collisions are easily managed, and semaphores are usually adequate as 
simple locking mechanisms if they are needed.


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