Thank you, @david_nova,

This issue is not general and it's only related to some cache solutions.

However, we're working on this and the PHP Session will be removed soon. I have no an exact ETA yet. At the moment you can disable the session by editing /wp-content/plugins/wpforo/wpf-includes/functions.php file. Find this code:

function wpforo_is_session_started(){
    if ( php_sapi_name() !== 'cli' ) {
        if ( version_compare(phpversion(), '5.4.0', '>=') ) {
            return session_status() === PHP_SESSION_ACTIVE ? TRUE : FALSE;
        } else {
            return session_id() === '' ? FALSE : TRUE;
        }
    }
    return FALSE;
}

Change it to this:

function wpforo_is_session_started(){
    return FALSE;
}

This will affect some notifications. So you may not see some notifications. For example after creating a topic, you'll not see a message in the top right corner "Your topic is successfully added" and so on. If the top right bubble notifications are important for you, you should wait for the removing PHP session in future releases. If these notifications are not important you can do the change provided above. This change only affects the top right green message box, nothing else.

Hi team Foro,

first of all I'm super grateful for the amazing work you guys do and I just want to let you know that I think WPForo is the absolute best forum plugin out there at the moment! I'm serious! And, anything I ask about removing User Session Cookies is in no way any criticism on the amazing job you guys do. I also bought almost all your add-ons when I first started using the plugin, just to support you guys (and because the add-ons are great of course) and I will keep doing that for as long as I use the plugin.

That being said, I hope my efforts can help me have a faster website for my visitors, maybe help the plugin be even more amazing, and potentially help a lot of users of the WPForo plugin to better understand this issue with caching that they might experience without even knowing it.

It took me months to figure out why my site was slow and caching wouldn't work. but, I found it. I did a lot of learning, and mind you, I'm still not an expert at all... so, please excuse any weird things I might say. 

Here is what I learned:

The function 'wpforo_is_session_started()'  called in a PHP file starts a unique user session by placing the PHPSESSID cookie locally in the browser of the visitor. If I understand it correctly the cookie is used to create a unique user session and store user data for the duration of that session (until the browser is closed and cookies are deleted). I also learned that Varnish Caching amongst most other caching solutions cannot serve the visitor any pages from the cache when there is a unique user session created by the cookie. Therefor when the cookie is present in the browser caching doesn't work and the pages are loaded in full from the server taking a lot more time. (in my case 4 seconds without caching instead of 1 second with caching). 

For the forum-pages itself this is not a problem at all, no caching solution should ever cache the forum-pages because you guys did an amazing job providing internal caching and other stuff to make the forum super fast. I made exceptions for all forum-pages in my caching. That works perfect and I'm thankful for how fast you made the forum.  

However, when the PHPSESSID cookie is placed in the browser by the WPForo plugin, it stays there. The caching solution I use (Varnish) sees the cookie and stops ALL caching. That means that when a user has the cookie stored in their browser, even the about page, blog posts, or home page which have nothing to do with the forum are not being cached anymore because the cookie is still in their browser. That, is the real problem I'm having. 

The result: The forum-pages on my website are super fast because you guys took good care of that, but the rest of the website is super slow because the PHPSESSID cookie remains in the browser and no caching occurs anymore for the rest of the website for as long as the cookie is stored in the browser.

In my previous post I wondered why after changing the code like @martin suggested, the PHPSESSID cookie was still being placed by the plugin. I did some searching myself. I went through all the PHP files that belong to the plugin and found 4 more mentions of the function 'wpforo_is_session_started()' in other PHP files. 

3x in class-notices.php

1x in wpf-hooks.php  

I'm assuming these files are still placing the session cookie in the browser and creating the same caching problem for me. 

My question is, can they be disabled in these two files just like @martin suggested for the functions.php file? 

And if yes, then what code should I use there as a replacement and what features would that affect? 

Also, are you going to address all of this in a future update so that the _session_started() is not used at all anymore by the plugin? I learned that besides caching issues this method also creates security issues. Most other plugins (Woocommerce, etc.) say they have stopped using this method because of that.  

Again, no criticism. Just hoping I can keep using WPForo for ever and ever.

Your help and efforts are greatly appreciated and if nothing can be done at this moment and I have to wait for the update that's fine, I have patience. I just think it's good to keep an open discussion about this.  

Thanks again for making this amazing plugin and taking the time to address this problem. 

Hope you guys have a great weekend!

This code replacement didn't resolve the issue for caching using SG Optimizer and the siteground.  

https://wpforo.com/community/how-to-and-troubleshooting-2/wpforo-making-site-slow-and-adding-no-cache-header-to-stop-sg-optimizer-for-caching/#post-44897