Performance question

zzz

I have a membership based site. When a user logs in I select account related data and set it in SESSION vars, like $_SESSION['myvar']. Currently it's about 40 vars per account. I do it on login once so that I don't have to query db when I need this data. Now, is it a good practice or would it be OK to query db whenever I need data? I basically use most of it anyways, but at least it's already available.

Say I have 1000 members logged in around the same time, that's 40K session vars set. Does that affect the performance of my server a lot? What is the best way to deal with similar issues?

nemonoman

If you query an individual element with an indexed search:
SELECT name FROM user WHERE id=12345
response time should be near instantaneous.

1000 concurrent sessions with 4000 bytes of session data each should also not be too big a deal. In the event of lots more sessions, this burden would affect performance. The point where performance suffers is not going to be known ahead of time.

So the individual database access method is consistent and economical. Put it on the list of things to get around to. If your traffic starts to increase, move it higher on the list of things to do.

Piranha

A thing to note is that data in the database can change, and then you won't have the correct information in the session variables. Of course, if only the user himself/herself can change the variable then it would be ok. But if an administrator can change it as well I don't think it is ok, in that case you defenetley should use database access every time.

etully

Does that affect the performance of my server a lot?

This is a good question to ask in a forum... you will get lots of good answers... but no matter what answers you get, you really should test this for yourself.

Learn to use Apache Benchmark (ab). It's a program that will hit your web site hard and tell you how many simultaneous users can be using your site. You can find out whether or not your site will run out of memory, slow down, crash the database server, etc.

All the advice and opinions in the forum are just gut feelings that we have based on the information you give us. Without actually knowing what brand of motherboard, which version of PHP, Apache, MySQL, which Linux kernel, which nic card, speed of your RAM, which CPU, which modules you have installed in PHP and Apache, your site's traffic patterns and how you have all your software configured, our performance estimates are only going to be ballpark estimates.

And besides, if we say that you should be fine and then the site crashes, do you really want to tell your boss, "The people at phpbuilder said it would work". If you load test it yourself, then you will truly know whether or not you're safe.

jazz_snob

Consider this: if you store them in session vars, then how are you storing that info server-side? The default is a flat file, which is slower than a database storage. If you do use database to store session data, then how much benefit can you really get? I think the point about session data getting 'stale' if someone changes something is important. Its a hassle to have to update that stuff. Better to store basic info in session and fetch it on each request, IMHO.

Optimize last---or never 😉

zzz

Well, this is a great discussion indeed!

I have addressed the issue of the stale sesions. If a user makes a change, the session is updated right away with the new data. Admin stay away from touching user accounts. It still appears to be a lot less code intensive when I just call a session as opposed to connectin to the db an getting it that way as well as I can allow user hop from page to page while loading their data from the sessions...

I think I need to do more traffic analysis to see what the users are doing on an average. If they do not use the pages I thought they would use most I may drop those sessions and use db calls.

I never heard about Apache Benchmark but it really sounds like something I ouhgt to investigate more. It might require me having a mirror site to run tests, but I think I like the idea of testing my server limits.

Fortunately I do not have a boss to report when I do something dumb. I just say: Dah!