Magento maintain various index tables to make data access faster. Magento core updates the indexes itself when you save a product but in some cases you may be required to update the indexes yourself. There are two ways to update the indexes from Magento admin or using the command line.
Updating Indexes from Admin
To updates index from admin follow the path Admin >> System >> Index Management
Updating Indexes from command line/shell
The command line script “indexer.php” is located in the “shell” directory of your Magento install. There are a number of options things you can do with this script.
Login with your SSH account and go to the shell scripts folder
Type the following to view the options available
php -f indexer.php help
In Magento there are 8 indexers, type the following to get the list of indexers
php -f indexer.php info
To view the current status of all indices type
php -f indexer.php status
To reindex you need to run commands like
php -f indexer.php -- --reindex catalog_product_attrbute
To rebuild all indices run the following command
php -f indexer.php reindexall
It is not recommended to execute full reindex in one step as it may overload the database server. Running indexer one by one will be faster and will generate less load on database server.