Question

As the notice is off in my php config it does not show notices in website.
But i can see a lot of Undefined index /undefined variable in the server log/php log

Will this affect system performance by any chance.

If i decalre these variable and assign null to these , error will go.
As it is defined.

Another doubt is , in some cases those variables will not be using.

So i declare and assign somany variable and if i am not using those variables . Will this affect the performance.

Answer 1

Nope.

None of your concerns are performance related.

Performance is not the only darn thing to care of.

I noticed some other questions of this kind recently (1),(2) and it’s scaring me.
Because these questions lacks very basic thing: a sense.

Every thing in this world has not only it’s cost but also it’s sense.
And I’d say that sense is main reason to prefer one thing over another.

Say, there are 2 kinds of dishes, a heap, filthy and dirty one vs. clean, healthy and taste but more expensive one. Would you always prefer only cheap one, just because of it’s cost? I doubt so.
Walking is great way to save a carfare. Do you always walk, no matter of the distance, obstacles and destination? Is cost being the only reason you’re taking into account? I doubt so.
You’re traveling by some vehicle sometimes, just because it’s more reliable way in certain circumstances. So, you choose things my sense, not by cost.

Same here.
If you have some errors in your code, these errors should be your concern, not related performance.
If you have your logs flooded with waste errors, obscuring real important ones, you have to turn these minor ones off. Not because of system’s performance but because of programmer’s performance, letting him get in touch with site heartbeat.

The sense, the meaning of the matter should be your concern. Not abstract “performance”.
There are languages apparently faster than PHP, say, assembly language for example. So, being concerned only in performance, you have to use assembly language only. But you choose PHP for it’s reliability. So, be consistent, choose things by their sense, not imaginary(!) performance.

When you’re asking about code structure, it’s reliable code structure should be your concern, not imaginary performance issues. Isn’t it obvious?