Log in to your account using SSH and Change to the directory where you installed Magento.
Run the blow given commands
touch /opt/ocentric/magento/current/maintenance.flag
service httpd restart
Then edit the index.php and assign the IPs to be shiteslited to the array $allowed = array(‘xxx.xxx.xxx.xxx’);
Log in to your account using SSH and Change to the directory where you installed Magento.
Run the blow given command
touch maintenance.flag
service httpd restart
Its also possible that we can the website accessible only for some given IPs
For that edit the index.php file and assign teh IPs to the array $allowed = array(‘xxx.xxx.xxx.xxx’);
Customer sessions stores data related to customer, checkout session stores data related to quote and order. They are actuall under one session in an array. So firstname in customer/session will be $_SESSION[‘customer’][‘firstname’] and cart items count in checkout/session will be $_SESSION[‘checkout’][‘items_count’]. The reason Magento uses session types separately is because once the order gets placed, the checkout session data information should get flushed which can be easily done by just unsetting $_SESSION[‘checkout’] session variable. So that the session is not cleared, just session data containing checkout information is cleared and rest all the session types are still intact.
HTTP is a session less protocol. A connection is made to transfer a single file and closed once the transfer is complete. This keeps things simple but it’s not very efficient.
To improve efficiency something called KeepAlive was introduced. With KeepAlive the web browser and the web server agree to reuse the same connection to transfer multiple files.
codePool is a tag which you have to specify when registering new module in app/etc/modules/Company_Module.xml
There are 3 codePools in Magento: core, community and local, which are resided at app/code/ directory.
Core codePool is used by Magento core team, Community is generally used by 3rd party extensions and Local codePool should be used for in-hour module development and overriding of core and community modules for custom requirement.
So in short, codePool helps Magento to locate module inside app/code/ for processing.
EAV is entity attribute value database model, where data is fully in normalized form. Each column data value is stored in their respective data type table. Example, for a product, product ID is stored in catalog_product_entity_int table, product name in catalog_product_entity_varchar, product price in catalog_product_entity_decimal, product created date in catalog_product_entity_datetime and product description in catalog_product_entity_text table. EAV is complex as it joins 5-6 tables even if you want to get just one product’s details. Columns are called attributes in EAV.
Flat model uses just one table, so it’s not normalized and uses more database space. It clears the EAV overhead, but not good for dynamic requirements where you may have to add more columns in database table in future. It’s good when comes to performance, as it will only require one query to load whole product instead of joining 5-6 tables to get just one product’s details. Columns are called fields in flat model.
