会话变量与Mysql表

Question

I'm planning on saving my users often used parameters, ie name, picture, etc, in session variables as opposed to pulling then from the MySQL table each time they are needed. Saving often used parameters in variables as opposed to a database in theory should be more efficient, but because I'm not sure how SESSION variables are saved I'm not too sure if this is true. Does anyone know if pulling info. from a SESSION variable is more efficient than querying the MySQL table?

The term variable is used loosely as SESSION "variables" are stored in files in the server's temporary directory.

You would think reading files is more costly than reading a database, I mean that is what a database is essentially, a file, but it is optimized for this purpose as opposed to "temporary session files"

Answer 1

Yes, pulling information from a session variable is more efficient than querying a database for that info. However, loading the information INTO the session variables requires reading a file off of your servers file system and into RAM, which depending on many factors (disk speed, IO load, db speed, etc) might be slower or faster than reading the same information from a DB. Without information on your specific setup, it's hard to say. One thing to keep in mind, if you plan on growing and using more than one web server, you will need to write some custom session handlers to either store your sessions to a central server (possibly a database), memcache, or a shared mount point where all your web servers can go to fetch the session files.

In the end, putting something into the session and using it from there can be more efficient than loading it from the DB every time, but you are still loading it from somewhere, and so, knowledge of your hardware and your setup will be your best guide.

Answer 2

The default Session handler for PHP stores that info to disk; one unique temporary file per session. The issues you may come across are if the disk/file system gets overloaded, or if your data becomes stale.

If you're making a trip to disk to access the session, there is slightly less overhead than accessing MySQL, but you're still making a trip to disk upon every page request. You can try to use an in-memory Session handler.

Answer 3

Session variables are preferred for persisting a relatively small amount of temporary data. They're good for "sessions".

Use a database for everything else. Especially for:

• larger amounts of data,
• for any kind of "transaction", or
• for data that needs to be persisted between "sessions".

This article is somewhat dated, and it doesn't apply to PHP per se ... but it should give you some idea about the relative efficiencies of filesystem (eg NTFS) vs database (eg MSSQL):

• To Blob or Not To Blob: MS Research white paper

Answer 4

Yes it's more efficient to use session variables. Typically Session variables are stored on the server in the /tmp directory (you can check your PHP Info file to see how yours is configured.

And because they're stored on the server, you can assume they're just as secure as the rest of your server.

Answer 5

Yes it is more efficient. Session is saved on server. However, with or without sessions you need to check if user is logged and if user has correct SESSION ID. It depends on number of your columns, rows and many other things