[Dbix-class] DBIx::Class::Fixtures speedup

[Jason Kohles]

On Apr 24, 2008, at 6:54 AM, luke saunders wrote:

> On Wed, Apr 23, 2008 at 8:42 PM, Matt S Trout <dbix- 
> class at trout.me.uk> wrote:
>> On Wed, Apr 23, 2008 at 04:37:54PM +0100, Drew Taylor wrote:
>>>> What if you used link() instead of a copy?
>>>>
>>>> Or just make the dump code make the tmp dir, and populate open a  
>>>> file handle
>>>> to everything in advance so you don't have to worry about paths  
>>>> changing
>>>> under you?
>>>
>>> As I understand your suggestion, dumping to the tmp dir wouldn't  
>>> work
>>> for me because I make a dump only every so often, but populate  
>>> from it
>>> many times per day as I run my tests. I just want to zip through the
>>> existing files w/o any IO other than reading/slurping the .fix  
>>> files.
>>
>> If dumping uses a temp dir, and populate just opens the filehandles,
>> that's exactly what you'd get.
>>
>
> Seems like a reasonable idea. My understanding here is that if a
> filehandle is opened and that file is then removed, the filehandle can
> still be read from. However I'm not clear on how that works,
> presumably Perl doesn't read the file into memory when you first open
> the handle, so what happens?
>
What happens (on reasonable OSes anyway) is that the original file  
still exists, even if there are no references to it in the directory  
structure.  In perl terms, you can think of both the directory entry  
and the filehandle as references, pointing to the same underlying  
data.  The file doesn't actually go away until it's refcount drops to  
0, which means that all the references to it in the directory  
structure are gone, and any filehandles that reference it are closed.   
If you delete the original directory entry that pointed to it, and  
create a new file in it's place, that reference doesn't point at the  
original data, it's a new reference pointing to a new chunk of data on  
the disk.

> Also I don't think link() works on all platforms.
>
This isn't entirely portable either, but I don't have any recent  
enough windows experience to say if it will explode on versions of  
windows released in this century or not...

-- 
Jason Kohles, RHCA RHCDS RHCE
email at jasonkohles.com - http://www.jasonkohles.com/
"A witty saying proves nothing."  -- Voltaire