PHP Session-like storage global across all users

Question

What is a good method to retain a small piece of data across multiple calls of a PHP script, in such a way that any call of the script can access and modify its value - no matter who calls the script?

I mean something similar to $_SESSION variable, except session is strictly per-client; one client can't access another client's session. This one would be the same, no matter who accesses it.

Losing the value or having it corrupted (e.g. through race conditions of two scripts launched at once) is not a big problem - if it reads correctly 90% of the time it's satisfactory. OTOH, while I know I could just use a simple file on disk, I'd still prefer a RAM-based solution, not just for speed, but this running from not very wear-proof flash, endless writes would be bad.

Dak

what's wrong with storing these values in a database? – Hipparch

You could use something like Memcached. – Steading

@SamuelCook: Rolling out whole SQL layer just to hold a 30-character string (about as much as I need to store)? Plus the database is on disk. – Dak

Answer 1

Take a look at shared memory functions. There are two libraries that can be used to access shared memory:

• Semaphores
• Shared Memory

For storing binary data or one huge String, the Shared Memory library is better, whereas the Semahpores library provides convenient functions to store multiple variables of different types (at the cost of some overhead, that can be quite significant especially for a lot of small-sized (boolean for example) variables.

If that is too complex, and/or you don't worry about performance, you could just store the data in files (after all, PHPs internal session management uses files, too....)

Orgiastic

It seems like Semaphores would solve my problem. I really don't need anything more heavyweight for like, 30 bytes of text? – Dak

Oh, and if it's only one string, I would prefer shmop_* functions (part of the Shared Memory library) over the shm_* functions that Semaphores provides. – Orgiastic

Answer 2

A good alternative to using a database would be memcache!

Differentia

According to this: we-love-php.blogspot.de/2013/02/… Memcached is quite slow (slower than a DBMS) – Orgiastic

Way too heavyweight for my liking. We're talking storing a single, small variable for goodness sake! Rolling out a separate daemon for that? – Dak

Then you should just use plain temporary files. PHP session handling doesn't do anything else. – Differentia