I've enabled the php_memcache.dll extension in php.ini.

Is that all i need to do?

Yes, to use the functions. You need a memcache server though, which I think only runs on Linux.

it won't work on Windows and i won't trust it to work correctly either.

run php either CGI or ISAPI mode. if you want speed go with ISAPI mode.

well it obviously works on livejournal, which it was designed for...

memcached actually works very very well.

What you have to remember tho, is that the memcached server will need plenty of RAM, as most of the data that it stores for you is help in RAM.

We have a client using it on a dedicated solution, and i must say the speed increace on the big queries they where running was impressive.

If you use some sort of DB abstraction, its pretty easy to setup in any application.

we use it to speed up our reporting, caching ldap queries as the time to retrieve the data is less than the overhead for the ldap query

very impressed actually, just added to the overall speed increase we were looking for

how does this compare to manually caching (saving it on file for later retrieval)?

memcache is designed to make that process faster, as it eliminates the hard drive from the sequence of components used to perform the query, as the relivant data is cached in the ram...

It works an absolute dream for vbulletin (so ive been told) the vbulletin forum absolutley love it.

say you were doing a lookup in a database of peoples birthdays, and you had 5000 people and their birthdays in a table, so you're (simplistic) connecting to the db, you're saying something like

select birthday from birthday_table where name = 'slidey';

and its going to the db, looking up the field in the table, and returning the birthday. say you want to do that a lot of times - it soon becomes a lot of work to connect to the database, do a lookup of the line(s) you want (which are stored in files somewhere on a disk) and return it to your program

what memcached will do is allow you to check in a seperate much faster database (for want of a different word, its not a database but a cache as it says on the tin!) for that entry, and return it. if not, you can then look in the slower database, and get your answer (which you'd then add to the memory cache)

we use it to speed up ldap queries, and store username-data pairs in our cache. speeds things up massively