Finding total number of active sessions

Question

I\'m a beginner to PHP and I\'m writing some code to my site. I want to get the total number of sessions that is active at that instant. I knew this is some difficult task b

Answer 1

All websites that allow you to show the number of visitors use database sessions handlers (it could be mysql db or even memcached).

Sessions table structure:

CREATE TABLE `sessions` (
`id` INT NOT NULL ,
`session_id` VARCHAR( 32 ) NOT NULL ,
`user_id` INT NOT NULL ,
`last_seen` DATETIME NOT NULL
) ENGINE = InnoDB;

Session ID could be either built-in php session id or your own unique hash. Built-in session works not so fast, but you don't need to watch for generating session ids, expiry dates and other.

User ID would be the current logged in user id, or NULL if he's a guest.

Every time user refreshes the page you should update your session table:

• Update last_seen if session already exists in database
• Add a new row for each new visitor that doesn't
• Change user_id value if user logging in or logging out
• remove expired sessions

At this point you can get all visitors count using simple sql query:

SELECT
    COUNT(`user_id`) AS users,
    (COUNT(*) - COUNT(`user_id`)) as guests
FROM
   `sessions`
WHERE
    `last_seen` >= DATE_SUB(NOW(), INTERVAL 15 MINUTE)