Efficient string generation and recycling. Help pls

Hi, I am programming in php, but that doesn't matter.
I need to be able to generate a one character or more string.
eg. "x5e5" to be put into a url like "mysite.com/x5e5"
after a period of inactivity i would like to delete it and reuse the string combination.

How should I generate a string without using a string that is in use?
Increment works, but it doesn't recycle the string.

HELP ME. thanks.

 

Use a table with a unique index on the string, the date it was created, and the date it was last used. You can check the status of any string with a select query, and you can generate a random string very easily.

 

If I generate a random string, it might generate a used string.
I would have to keep generating random strings indefinitely to get an unused string?

 

Use incrementation and add recycling to it.

The first few strings will be generated in alphanumeric increments. Setup a CRON job that runs regulary and have the script check through all strings and make note of any expired ones. Now when you need to get a new string, it first checks your store of expired strings and takes one from there if possible. If there aren't any, it generates one using an incrementation of the last string.

That's just one way, there may be a better way but I can't think of anything atm.

 

Alternatively, you could always just set a table up with a heap of possible strings already defined, then assign URLs to those strings as you want. When you want to undefine a URL, just remove it but keep the string 'key' in the database. When you want to find the 'next' available string, a quick SQL query of something like 'select id from table where not assigned limit 1' will give you that 'next' unused key.

As the need arises, just add more keys (this could be done automatically almost).