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Posted by Jason Barnett on 05/17/05 00:54
Evert | Rooftop wrote:
> Hi,
>
> I'm developing a cache system. Which works in pseude code, like this:
>
> class Cache {
>
> function Fetchdata($id1,$id2,$id3) {
>
> $id = md5($id1 . $id2 . $id3);
> if ($this->DataIsExpired($id)) return false;
> else return unserialize(file_get_contents($id));
>
> }
>
> function storeData($data,$id1,$id2,$id3) {
>
> $id = md5($id1 . $id2 . $id3);
> OpenTheFileAndWriteTheDataSerialized($data);
> }
>
> }
>
> $id1 $id2 and $id3 are when they are combined unique
>
> * Is there a chance of collision when MD5 is used on the id's and the
> ids are long strings
Yes there is a chance, but it's small enough that for practical purposes
you can ignore it.
> * Is file_get_contents the fastest way to open the file?
AFAIK yes it is since it takes advantage of memory mapping (where possible).
> * Is serialize the fastest way to serialize ;) ?
Not sure.
> * Are there any other things I should consider? (I'm aware of
> file-locking issues, and have taken care of that)
>
> regards,
> Evert
Hmmmm... well, file_get_contents() doesn't lock the file so I'm
interested in how you're accomplishing this feat. Perhaps you're
creating a temporary directory (atomic IIRC) for the filename and then
flocking that? I dunno, I hate race conditions.
You might also want to consider the security of the data that goes into
your cache'd $_APP data. Because any file that is created by PHP is
going to be in pretty much the same boat as the default session files
and on a shared server, well...
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