Nightly truncating all cache_* tables? Good or bad?
Cron job to truncate the tables might cause some metadata locks due to the TRUNCATE command being a DDL statement; depends on how busy your server is. What APDQC does is a table rename swap and then truncate; if you did something similar then you should be ok. APDQC will also use gzip to make the table sizes smaller; something that would be a benefit in your case. Without compression our DB cache tables would take about 50GB, they now take about 12gb.