Re: Implementing database cache.

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Bruno B B Magalhães wrote:
> does anybody have am idea of witch are the required functions to
> implement a database query cache? I have a very nice and fast database
> layer, witch I use in all my projects (about 19 sites and a lot of
> others hot-sites and systems like intranet and extranets). Here is my
> idea of the functions:
>
> is_cached();
> read_cache();
> clear_cache();
> write_cache();
>
> And what is the fastest way, shared memory perhaps? And I would have to
> use serialize function to store query results right? and about the
> cache name (or cache_id whatever) I was thinking about using a md5 hash
> of the query itself.
>
> I would love any ideas! :)

1. Rolling your own database cache is probably not a fruitful exercise,
except as a learning experience.  Honest.  The database vendors already
have a cache you can use, and you're not going to beat their performance
with your own in any kind of reasonable development time-frame.

2. You can't serialize the objects, connection, or result, from MySQL
functions.  I'm 100% certain of the connection object, and 99.9% certain
of the result set object.  Those objects go invalid when a script ends, no
matter how you try to save them.  You'll have to suck out all the data and
store that.

3. Shared memory, last time I checked, was a real [bleep] to use because
of a race condition in getting a unique name/semaphore for the storage
space on a server-wide basis.  Maybe this has changed since I last looked,
but back in the day, you were taking the risk that your PHP shared memory
would get trashed by, say, Perl using shared memory.  Or any other
application that wanted to use shared memory.  I *hope* this has been
fixed, for your sake, but be sure you read up on it.

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