Brett

Frontend Features: 
 – adds a toolbar to the bottom of WordPress pages that will show meaningful information that helps developers to create optimized WordPress sites. 
 – Info includes SQL queries, query vars, peak memory usage, and a filetrace.
Backend Features: 
 – Provides a very basic checklist with suggestions for development. 
 – Shows basic server stats and information 
 – phpInfo 
 – WP rewrite rules (coming soon)

Developer Toolbar

Adds easy to access data for developers, including a fixed toolbar to the bottom of pages that shows query data and memory usage among other data.

tombenner

MySQL Profiler displays debugging information about SQL queries to admin WordPress users. For each query, the profiler displays the time, syntax-highlighted SQL, and a trace of the functions (as well as the file and line number that the functions were called from) that were called.
The list can be sorted by any of its columns, so you can, for example:
<ul>
<li>Order the list by ID to see the chronological order of the queries</li>
<li>Order the list by time to see the slowest queries</li>
<li>Order the list by query to group the queries by type (SELECT, UPDATE, etc)</li>
<li>Order the list by trace to group the queries by similar origins</li>
</ul>
The list can also filtered by typing in the search box, so you can, for example:
<ul>
<li>View all queries that use the wp_posts table</li>
<li>View all queries that are related to the use of a function in taxonomy.php</li>
<li>View all queries that are related to the use of a specific function or class</li>
<li>View all queries that call a specific MySQL function</li>
</ul>
To turn off syntax highlighting, put the following in wp-config.php:
<pre><code>define('MP_HIGHLIGHT_SYNTAX', false);
</code></pre>
To omit the file and line number from the function trace and display the functions as a comma-separated list (to save vertical space), define the following in wp-config.php:
<pre><code>define('MP_DISPLAY_FILES', false);
</code></pre>
This plugin was loosely based on <a href="http://bueltge.de/" rel="nofollow ugc">Frank Bueltge</a>‘s <a href="https://wordpress.org/extend/plugins/debug-queries/" rel="ugc">Debug Queries</a> plugin, so a hearty thanks to him for the development of that.
If you’d like to grab development releases, see what new features are being added, or browse the source code please visit/follow the <a href="http://github.com/tombenner/mysql-profiler" rel="nofollow ugc">GitHub repo</a>.

MySQL Profiler

Displays a list of each page's SQL queries and the functions calling them that can be searched and sorted by time, type, etc.

Developer Toolbar vs MySQL Profiler