Re: DBWR Tuning

From: Denis Do <nospam.denisdo_at_yahoo.com>
Date: Mon, 13 Dec 2004 06:53:28 GMT
Message-ID: <slrncrqf56.3vo.nospam.denisdo@denisdo.news.google.com>

... skipped about number of DBWriters ... Niall,

I want to explain why I would do this.
1st, obviously he has at least 2 CPUS - and not only one HDD, I assume (see original post).
In such situation it is better to have 2 or even more DBWriters - that will help you distribute your load between CPUs and IO between drives, also consider the fact that the system is OLTP, so you need scan LRU list for quick blocks fast. You do not use IOSlaves on OSs with real Async IO, that is why we are talking about DBWriters, not slaves.

These were my reasons, and I would set 2 DBWriters in such situation.

About wait times - yes, you are right - but in this situation having one "excessive" DBWriter will let us chance to "catch up" with dirty blocks quicker, if need arises. That has bigger advantage, comparetively to overhead involved in maintaining second writer. And anyway, if you have more complicated file structure than one HDD:-), you will need additional Writer, on both stripe and mirror.

Can you please highlight your points why you do not set up second (or even third) writer in this scenario?

Have a great day! :-) Received on Mon Dec 13 2004 - 00:53:28 CST