mysql not starting after deleting the database from the mysql datadirectory

Few days back i have mistakenly deleted one database folder directly from the mysql data directory but still the site was working fine. I just wondering how its working? 

So i restarted the mysql service. It stopped but didn’t start and getting below error in the log file

[root@localhost html]# tail -f /var/log/mysqld.log

InnoDB: Error: log file ./ib_logfile0 is of different size 0 84992 bytes

InnoDB: than specified in the .cnf file 0 5242880 bytes!

131001 17:54:45 [ERROR] Plugin ‘InnoDB’ init function returned error.

131001 17:54:45 [ERROR] Plugin ‘InnoDB’ registration as a STORAGE ENGINE failed.

131001 17:54:45 [ERROR] Unknown/unsupported storage engine: InnoDB

131001 17:54:45 [ERROR] Aborting

131001 17:54:45 [Note] /usr/libexec/mysqld: Shutdown complete

131001 17:54:45 mysqld_safe mysqld from pid file /var/run/mysqld/mysqld.pid ended

As usual i started searching google and didn’t find any solution and final got one solution. It’s to delete the ib_logfile0, and i deleted it and trying to start the mysql service and it start working  by recreating this file automatically…

What i understand from this, if you going to re-install the mysql or wamp server and to take backup of these databases, you have to follow below instructions,

  1. First stop the mysql service
  2. Copy the database which you need to have backup from the mysql data directory 
  3. Re-install / Install either Mysql or Wamp Server
  4. Stop the mysql service
  5. Paste the database backup in the mysql data directory which you have taken previously
  6. Start the mysql service

This will keep the old database backup easily without any problem and this will avoid importing the database again. May be imporing small database is not a problem, but thing when you have some 1GB or @ GB size of db, then it will take more time to import the database. Following the above steps, will save your time.

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The site is currently not available due to technical problems. Please try again later. Thank you for your understanding.

If you are the maintainer of this site, please check your database settings in the settings.php file and ensure that your hosting provider’s database server is running. For more help, see the handbook, or contact your hosting provider.

There are two things you need to check.

1. Is mysqli is installed or not?

2. Is server able to connect database?

Is mysqli installed or not:

Check info.php file is mysqli is listed in this page, if not then your server will support only mysql not mysqli. If your host doesn’t have mysqli installed, you can it change to use mysql. (MySQLi stands for MySQL Improved.)

Open settings.php change $db_url from mysqli to mysql (settings usually in /sites/default-folder in your drupal installation).

BEFORE:
$db_url = ‘mysqli://user:password@hostname/table’;

AFTER
$db_url = ‘mysql://user:password@hostname/table’;
This means that you can either install MySQLi with your PHP install OR you can simply make the changes to your settings.php file as detailed above.

 Is server able to connect database?

Check whether you have passed right username, password and database name and also check whether you have given full permission to access the database from the server.

Hope this will be useful for those having similar problems.

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