Multi-threaded replay of master activity for load/performance testing
I actually have a suggestion that will take some work but is doable.

THEORETICAL SCENARIO


You have 3 databases: db1, db2, db3
Production DB had binary logging enabled


What you need are the following to create enough traffic:


mysqldump of Production DB two weeks old (TwoWeekOldData.sql) of db1, db2 and db3
Binary logs on Production DB that are two or more weeks old
Four DB Servers running MySQL


DBServers 1-3 are Slaves to Production DB
DBServers 1-4 have Binary Logging Enabled
DBServer1 has replicate-do-db=db1 and has only db1 data loaded
DBServer2 has replicate-do-db=db2 and has only db2 data loaded
DBServer3 has replicate-do-db=db3 and has only db3 data loaded
DBServer4 has all data from TwoWeekOldData.sql loaded



You will need the following:


Run mysqlbinlog against all binary logs on Slave1 and collect SQL into db1traffic.sql
Run mysqlbinlog against all binary logs on Slave2 and collect SQL into db2traffic.sql
Run mysqlbinlog against all binary logs on Slave3 and collect SQL into db3traffic.sql
Run these three traffic SQL files in parallel like this


mysql -hdb4 -u... -p... -A -Ddb1 &lt; db1traffic.sql &amp;
mysql -hdb4 -u... -p... -A -Ddb2 &lt; db2traffic.sql &amp;
mysql -hdb4 -u... -p... -A -Ddb3 &lt; db3traffic.sql &amp;

You can use DBServer4 to measure


server load
query performance 
I/O utilization
Whatever you want to measure



As I mentioned in the outset, this takes some setup work along with access to old data and all binary log entriers since the old data's last backup.

I hope this gives you some guidance on producing real traffic rather that simulating ordinary load.

GIVE IT A TRY!!