使用流量较高的$ _Session变量

Question

I am working on a quick survey for a company who will be getting about 200k (at peak) visitors hourly for about 2 days straight. I was just wondering if using $_SESSION variables would tie up the server. All that we are storing in those variables are at most a 6 character string or a single digit integer. I'm new to the PHP world so I'm not sure how reliable or how much $_Session variables will tie up the servers. The servers we are using will be cloud servers. One final note is that the the sessions will only last maybe 6 - 10 minutes tops for each visitor before I close it out.

Any help will be greatly appreciated!

Answer 1

By default, data in $_SESSION will be written to disk upon each call to session_write_close(), or upon script termination. There is no way to know for sure how this will perform without testing the final application on the server hardware you will be using. Since the volume of data is small, the real worry is disk latency. An easy workaround for this would be to set PHP's session_save_path to an in-memory filesystem.

Answer 2

Tie up how? Disk space? Storing a simple 6char string using the default file-based session handler will take up about 6+length-of-variable-name + ~6 chars of space on the disk. There'll be some overhead to load/unserialize the data in the session file. but it'll be much less than the initial overhead of loading/compiling the script that's using the session data.

Remember, PHP's default sessions use the disk as their storage media - they're not persisted in memory after the script exits.

Answer 3

In PHP you can change the session handler. The default session handler is to write data in a temp file, with one file per session. It works okay, but has limitations when runnning high traffic apps (although with 200K/hour you shoudln't have problems with the default handler).

And easy solution is to use the session handler for Memcached, with the PECL/Memcache extension (not to confuse with the PECL/Memcached extension):

http://www.php.net/manual/en/memcache.examples-overview.php (see example #2)

Answer 4

I think you don't want to store data in sessions, because it writes to disk. If someone hits the app with multiple requests, are you able to guarantee that they hit the same machine in the cloud? That's rather complicated to write. I would cookie the user instead.

http://php.about.com/od/learnphp/qt/session_cookie.htm

http://www.quora.com/Does-PHP-handle-sessions-by-writing-session-variable-data-to-disc-or-does-this-information-persist-only-in-RAM-Will-accessing-session-data-cause-a-disc-read-in-PHP

Like the others said, I'd use Memcached if you want to scale, but to answer your question directly, I think your server should be able to handle the usage you describe.