Difference between InnoDB and MyISAM?

Three Major Difference:

• First major difference I see is that InnoDB implements row-level lock while MyISAM can do only a table-level lock. 
• You will find better crash recovery in InnoDB. However, it doesn’t have FULLTEXT search indexes, as does MyISAM.
• InnoDB also implements transactions, foreign keys and relationship constraints while MyISAM does not.

How to create the table using module?

/**
* Implements hook_schema().
*/

function module_name_schema() {
$schema['module_name'] = array(
‘fields’ => array(
‘type’ => array(‘type’ => ‘varchar’, ‘length’ => 15, ‘not null’ => TRUE, ‘default’ =>
‘node’),
‘id’ => array(‘type’ => ‘int’, ‘unsigned’ => TRUE, ‘not null’ => TRUE, ‘default’ => 0),
‘module_name’ => array(‘type’ => ‘varchar’, ‘length’ => 255, ‘not null’ => TRUE,
‘default’ => ”)
),
‘primary key’ => array(‘type’, ‘id’),
);
return $schema;
}


/**
* Implements hook_uninstall().
*/

function module_name_uninstall() {
// Clear variables
variable_del(‘module_name_default’);
}

Use db_drop_table method in install file to drop the table using module.

How can we improve the Drupal site performance?

To increase the Drupal Site performance, try for below mentioned things,

1. Use PHP APC, 
2. Use memcache, 
3. Use the Varnish. 

Most important module

• Use the Boost module. 
• Use Views Cache.

For very high traffic, 

• Use the CDN module. 
• Use the Block Cache.

Debug Code in Drupal

Simple using print_r or var_export , you can debug code within Drupal.

<?php
$node = node_load(123);
print_r($node);
?>

Drupal devel module provides dsm and dpm functions to debug code within drupal.

<?php
$node = node_load(123);
dpm($node);?>

drupal latest version provides debug inbuilt function to print errors, notices and warnings as well.This could be in the page or in the logs depending on how php is configured.
For example,

<?php
$node = node_load(123);
debug($node);
?>

The full options for debug function are:
debug($data, $label, $print_r);

The $data is pretty self explanatory. It can be anything you could pass
through print_r or var_export. The $label allows for a custom label to be
added. This is ideal when you are sending the information to a log and you
want a key to search the logs for. The 3rd argument is whether to use print_r
or var_export. The default is var_export. If you are interested between the
two I’d suggest reading the manual pages.

Upgrade Drupal Versions and Modules

Steps to Upgrade drupal minor version.

1. Backing up the site,
2. Putting it into maintenance mode
3. Downloading the new version of the module
4. Uncompressing it
5. Running update.php
6. Testing the site
7. Taking the site out of maintenance mode
8. Steps to Upgrade Drupal major version.

Backup your existing site and database.

1. Log in as user ID 1
2. Put your site in maintenance mode
3. Change all themes to Garland
4. Disable non-core modules
5. Remove default settings file
6. Remove all old core files and directories
7. Remove uninstalled modules
8. Download Drupal 7
9. Re-apply modifications to core files
10. Make your settings.php file writeable
11. Run the update script
12. Backup your database
13. Upgrade fields
14. Update contrib modules and themes
15. Check the Status Report
16. Make sure settings.php is secure
17. Check Drupal Core Modules
18. Remove your site from Maintenance Mode

To find day, month, week and year difference between two dates using jquery

<script>
function getDateDiff(date1, date2, interval) {
    var second = 1000,
    minute = second * 60,
    hour = minute * 60,
    day = hour * 24,
    week = day * 7;
    dateone = new Date(date1).getTime();
    datetwo = (date2) ? new Date().getTime() : new Date(date2).getTime();
    var timediff = datetwo - dateone;
secdate = new Date(date2);
firdate = new Date(date1);
    if (isNaN(timediff)) return NaN;
    switch (interval) {
    case "years":
        return secdate.getFullYear() - firdate.getFullYear();
    case "months":
        return ((secdate.getFullYear() * 12 + secdate.getMonth()) - (firdate.getFullYear() * 12 + firdate.getMonth()));
    case "weeks":
        return Math.floor(timediff / week);
    case "days":
        return Math.floor(timediff / day);
    case "hours":
        return Math.floor(timediff / hour);
    case "minutes":
        return Math.floor(timediff / minute);
    case "seconds":
        return Math.floor(timediff / second);
    default:
        return undefined;
    }
}

getDateDiff('1948/11/12', new Date(), 'months');

first parameter should be the date from where you want to know the diff.

second parameter should be the present date or whatever you wish

Third parameter should be the type of diff that you want between the two dates. (ex. years, months, weeks, days, hours, minutes, seconds)

</script>