Why session custom data lost after refresh in Magento 2?

Question

I need to save data in session on one page and retrieve same data on multiple pages. After saving the data when i refresh page Or redirect to another page data flush off . Can somebody explain me why it's happening? What can do to fix this?

I have tried with all types of sessions in magento2(customer,checkout,backend,catalog) also phpsession($_SESSION) without any luck.

am using Magento 2.1.7 with Luma Theme.

Any help will be really appreciated.

Answer 1

For Catalog, Checkout, Customer and other Magento session like

\Magento\Catalog\Model\Session
\Magento\Checkout\Model\Session
\Magento\Customer\Model\Session

Because Magento 2 is no longer using core session like in magento 1.

protected $customerSession;
public function __construct(
    ....
    \Magento\Customer\Model\Session $customerSession, 
    ....
){
    ....
    $this->customerSession = $customerSession;
    ....
}

To set and get the value of session.

$this->customerSession->setCustomerName('Bob'); //Set Value
$this->customerSession->getCustomerName(); // Get Value
$this->customerSession->unsCustomerName(); // Unset Value

You can use above Factory method by creating function or directly by using objectManager

$objectManager = \Magento\Framework\App\ObjectManager::getInstance();
$customerSession = $objectManager->create('Magento\Customer\Model\Session');
$customerSession->setCustomerName('Bob');
$customerSession->getCustomerName();

Answer 2

You may have exceeded the string length limit for storing data in the session. Just increase this value from Magento admin panel (Stores > Configuration > Advanced > System > Security).

Details:

Data which Magento saving each time (almost on each request) looks like this (it is a part of real data):

As you can see at the bottom of screenshot it is 285934 chars length. But Magento (2.4.1 in my case) has own properties named "Max Session Size in Admin" and "Max Session Size in Storefront" which add limits to the maximum allowed size of that string. Default value of that settings is 256000 and it is less than size of real data in my case.

What Magento does? It adding notification message in the log file, and save nothing new... but did not delete old value.

Here is that part of code from ./vendor/magento/framework/Session/SaveHandler.php:

Checked in debugger: