Something doesn't sound like it's setup properly. There was a time that I had more then 100 slaves connected to a master. Many reads and writes occurred on the masters and all slaves kept up.
I suspect that your running out of IO bandwidth on a slave from a table scan or huge and frequent sorts. DVP ---- Dathan Vance Pattishall http://www.friendster.com > -----Original Message----- > From: Kevin Burton [mailto:[EMAIL PROTECTED] > Sent: Tuesday, June 21, 2005 6:01 PM > To: mysql@lists.mysql.com; [EMAIL PROTECTED] > Subject: Possible to DoS a slave by using multiple > connections on the master!. > > Not sure if this is a known issue or not.. but I haven't seen > it documented anywhere. > > Anyway. My past thinking was that you should always use as many > connections as you have tables (at least with myisam). This > way in the > worst case scenario you could have locks open on all tables > instead of one lock on one table holding back all other tables. > > This is a BAD idea if you're trying to reach max qps with INSERTs. > > What happens is that the disk controller is able to command > queue (and other opterations) to optimize IO on the master > since technically you have multiple INSERTs happening at once > (one for each table). Then on the slave since there's only > one thread replaying the DML it will back up since the disk > controller isn't able to optimize the IO. > > We were actually running a master with RAID5 and a slave with > RAID0 and the slave still couldn't keep up. The problem was > only fixed when we told our client to only use one connection. > > While this is a temporary fix this limits the scalability of > MySQL as I could easily see a LOT more QPS going through these boxes. > > It might be possible place an intelligent scheduler to bulk > up INSERTS and use FK relationships to allow non-dependent > SQL to pass forward. > You could also have one thread per slave per connection on > the master. > Then in the binary log you could flag the thread ID that > performed the modification on the master and use the same > thread on the slave. > > The downside being that you'd need more resources on SLAVE boxes. > > Seems like a wiki page in the making........ > > -- > > > Use Rojo (RSS/Atom aggregator)! - visit http://rojo.com. > See irc.freenode.net #rojo if you want to chat. > > Rojo is Hiring! - http://www.rojonetworks.com/JobsAtRojo.html > > Kevin A. Burton, Location - San Francisco, CA > AIM/YIM - sfburtonator, Web - http://peerfear.org/ GPG > fingerprint: 5FB2 F3E2 760E 70A8 6174 D393 E84D 8D04 99F1 4412 > > > -- > MySQL General Mailing List > For list archives: http://lists.mysql.com/mysql > To unsubscribe: > http://lists.mysql.com/[EMAIL PROTECTED] > > -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
