[wp-hackers] What were the shared hosting issues with persistent file cache prior to WP 2.5 ?

[Otto]

On Tue, Nov 2, 2010 at 10:18 AM, Kaloyan Tsvetkov <kaloyan at gmail.com> wrote:
> I am doing some research on file-based caching and I read that persistent
> cache was removed from WP since 2.5 and was replaced with in-memory one. The
> reason for that were that the WP implementation was hardly introducing any
> performance boost and that there were some issues with shared hosting.
>
> Does someone recall what these issues were, or at least where I can read
> about them ?

What Peter said. A large number of hosts use shared filesystems
(especially "cloud" hosts) and accessing the filesystem over the
network (be it via NFS or any other means) is slow.

Also, even local filesystem access frequently isn't really any faster
than database access in many cases. For example, if you're running a
database server on the same machine, then the SQL query cache probably
is storing a lot of the results of your common queries in RAM. Much
faster to get them from there than to go load a file. Filesystem
caching generally isn't very aggressive and so hits to that cache
often miss, requiring it to go back to the disk.

Like all things, it depends on the specific details of your setup.
This is why it's best left to plugins to allow you to optimize as
needed for your particular circumstances. If you have a big site, best
way to do it is to use some kind of distributed memory caching, like
memcached, for caching persistent objects.

-Otto