Tcl packages like mytcl & mysqltcl can provide an interface to a mysql database.
Each time eggdrop updates it's userfile, it would lockup until it is complete. Even with only a handful of 20 users. It would have to check there flags, channel flags, info lines, XTRA info, passwords, hosts. CHannel flags, XTRA & hosts would require extra calls to the SQL server, as there could be multiple values.
In this situation, on a bot with 4 channels, 20 users, 2 XTRA lines per user, 3 hosts per user. It would take about 3 seconds per user to preocess, multiply this by the 20 users and you bot will be lcoked out for almost 1 min. This is a long time to be locked up in a script, and is more that bound to cause a ping timeout for each update.
This is only with a base of 20 users. If you are talking 50 possibly 80 users, lockups of 2 1/2 to 4 mins.