1. System configuration
If your web server (Apache, NginX, etc) and database server (MySQL) exist on the same server (hardware), you should try to changing system parameter of qa-config.php (around L166). This change reduces the load on your server, and performance of your site will be improved. As a result, you may be able to avoid the phenomenon.
Before (Current setting):
define('QA_OPTIMIZE_LOCAL_DB', false);
After:
define('QA_OPTIMIZE_LOCAL_DB', true);
2. Size of your qa_options table
You should change again the system configuration of the qa-config.php according to the advice of maxj. And, report the number of records of qa_options table on your debug panel (bottom of page). If this number is very large (more than 5000, 10000, 100000, etc), you might need to remove the unnecessary records in the qa_options table.
Before (Current setting):
define('QA_DEBUG_PERFORMANCE', false);
After:
define('QA_DEBUG_PERFORMANCE', true);
Example of debug panel:
SELECT title, content FROM qa_options
13.31 ms - 1841 rows - 2 columns
3. MySQL configuration
If you are using VPS or dedicated server, you need to check MySQL configuration below (my.cnf). You may be able to check these settings in phpMyAdmin.
max_allowed_packet
read_buffer_size
max_used_connections
etc ...
http://forums.mysql.com/read.php?22,593241,593241