MySQL: How to find MySQL 5.1 (with built-in InnoDB) or MySQL 5.1 (with InnoDB-plugin)? My DB server has MySQL 5.1.58-community-log and I am planning to upgrade it to MySQL 5.6 with specific purpose of improving my system performance and removing the bottleneck issue.
So, I have gone through mulitple posts about the differences between MySQL 5.1 and MySQL 5.6

Below article indicates that MySQL 5.1 has better performance than 5.6
https://serverfault.com/questions/362388/mysql-5-1-vs-mysql-5-5-5-1-twice-as-fast/362706#362706

http://www.mysqlperformanceblog.com/2011/10/10/mysql-versions-shootout/

There are two versions of MySQL 5.1 as below:

MySQL 5.1 with built-in InnoDB
MySQL 5.1 with InnoDB-plugin



What are the differences between these?  
How will I know that My server has built-in InnoDB or InnoDB-plugin? 
How to change from built-in InnoDB version to InnoDB-plugin version and vice-versa?
Should I not leave my plan to upgrade MySQL?
If it's a plugin then you'll see variable innodb_version:

mysql&gt; show variables like 'innodb_version';
+----------------+----------------+
| Variable_name  | Value          |
+----------------+----------------+
| innodb_version | 5.5.35-rel33.0 |
+----------------+----------------+


InnoDB as a plugin had more features and was more actively developed. That happened due to historical reasons (at that time MySQL was owned by Sun and InnoDB was owned by Oracle). 

I wouldn't recommend using 5.1 as it's EOL. 5.1 isn't any faster than 5.5 or 5.6. Why would it be if the huge team in Oracle works on InnoDB  and 5.5 and 5.6 are great releases. It reminds me common myth "MyISAM is faster than InnoDB".