MySQL read/Write very slow in a table because of long blob columns

Today I was digging a mysql performance drop issue.  The symptom is query very slow when selecting in

one table.   I tried to use explain comment, but it returns very fast.    Therefore, I just select 1 column in the 

same time to find out which column was cause.   Finally, I found it was a blob column.    Use blob and mysql

to google, there are a punch reference in there