Pythian Group

I’ve been following the discussion in various MySQL blogs regarding the sort_buffer_size parameters. As an Oracle DBA, I don’t have an opinion on the subject, but the discussion did remind me of many discussions I’ve been involved in. What’s the best size for SDU? What is the right value for OPEN_CURSORS? How big should the shared pool be?

All are good questions. Many DBAs ask them hoping for a clear cut answer – Do this, don’t do that! Some experts recognize the need for a clear cut answer, and if they are responsible experts, they will give the answer that does the least harm.

Often the harmless answer is “Don’t touch anything, because if you have to ask this question you don’t have the experience to make the correct decision”. As Sheeri noted, it is a rather patronizing answer and it is stands in the way of those who truly want to learn and become experts.
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In How to tune MySQL’s sort_buffer_size, Baron gives a condescending viewpoint on how to tune the sort_buffer_size variable in MySQL. In a much-nicer-nutshell, his advice is “do not change sort_buffer_size from the default.”

Baron did not explain the logic behind his reasoning, he handwaves that “people utterly ruin their server performance and stability with it,” but does not explain how changing the sort_buffer_size kills performance and stability. Regardless of how respected and knowledgeable the source, NEVER take any advice that tells you what to do or how to do it without understanding WHY.

This article will explain the “why” of Baron’s point, and it will also talk more about understanding why, an integral part against the “Battle against any guess.” Baron’s recommendation to leave sort_buffer_size as the default is just as bad as all the advice given to change the sort_buffer_size, because all that advice (including Baron’s) does not explain the underlying causes.

First, I explain the sort_buffer_size issue. Read the rest of this entry . . .

In The Doom of Multiple Storage Engines, Peter talks about how the storage engine concept of MySQL is usually spoken of in positive terms, but there are many negatives.

I have a hard time trying to figure out the deeper meaning behind Peter’s post, given that Percona writes a storage engine for MySQL, XtraDB. Does this mean that Percona will stop developing XtraDB? Does this mean that the Percona Server will diverge farther and farther away from MySQL so that they’re not compatible any more and migrating from MySQL to Percona Server is very difficult?

Or maybe it’s just that Peter is saying one thing and doing the opposite; which just seems wrong because that would be blatant hypocrisy on Percona’s part.

(This idea was a comment on the blog post but seems to be trapped in the spam filter, so I’m posting it; apologies if the comment comes through eventually….)

My own opinion of the issue: Peter is factually correct with what he says. However, it’s nice to have the framework and be allowed to use more than one storage engine, or use exclusively one storage engine that’s not MyISAM.

I’ve never attended the North California Oracle User Group Conferences even though they are organized every quarter. However, I’ve been always jealous of the great agenda they put together. A couple months ago, Chen Shapira reminded me once again that the next NoCOUG conference was coming up and asked whether I would be able to come to present. What a chance, I thought, easy to plan as I have no other conferences in May.

So, at NoCOUG Spring Conference 2010 in just 10 days, I’ll be doing my two hour long presentation — Demystifying Oracle RAC Workload Management. If it’s your local conference, I hope you can attend and say hello. You might also want to download the whitepaper that I put together few years ago for Hotsos Symposium — Oracle RAC Workload Management.

The conference is free to members of NoCOUG and only $50 to non-members but it would make more sense to just join the user group as its annual fees are unbelievably low — I couldn’t say it better than Iggy Fernandez did:

How much does a NoCOUG membership cost? It doesn’t cost $400, as you might expect to pay for so much educational value. It doesn’t cost $300 and it doesn’t cost $200. It doesn’t even cost $100. Yes, a calendar-year NoCOUG membership only costs $95! Won’t you join today?

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Video fragments of my session posted at the end — read on.

I arrived at Omni Mandalay Hotel on Sunday evening with Dan Norris. I was flying through Chicago and it turned out that Dan was on the same flight and only few rows behind me. Small world.

Preparations for the conference were very chaotic on my part and, of course, I didn’t have either of my presentations ready. I was very stressed and getting sick as well — it looked like a complete disaster waiting to happen. I’d like to say that I was feeling like Doug Burns as he often managed to get sick just before a conference. Of course, I worked on my slides for the last few days as well as on the flight and presentation was slowly getting there but boy was I tired!

I quickly said hello to the crowd in the bar on the way to my room and rushed away to do some more damage to my slides. And then I had a brilliant idea — I could still see one of my best mates and do something good about my presentation! I asked Doug if he was interested in the preview (he probably wasn’t interested but he couldn’t say it to me) especially that my session wasn’t on his original agenda. Of course, that would mean that he had to leave a bunch of other good friends and spend some time tete-a-tete. Knowing Doug, this is some of the hardest thing to ask from him but it shows how good of a friend he is! (Plus, everyone thinks that he is anti-social anyway. Shhhh!)
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Just a quick post to get myself back into blogging mode. Recently in IRC (#oracle on freenode, to be precise), a fresh face asked if the Block Change Tracking file ever shrinks. She had been worrying about the file in her instance continuing to grow. A number of us speculated (non-BAAG!) that perhaps taking an RMAN backup would somehow purge the file of what it was keeping track of, and then the magical Oracle fairies would promptly resize it for us. Needless to say, I was hesitant to take this theory forward with Alex Gorbachev aware of my home address.

After setting up Oracle 10.2.0.1 on a nice VirtualBox image
(more on that in another post) running CentOS 5, I began to do some reading. For some reason, actually reading the official tahiti docs was last on my list. A search of the 10gR2 docs quickly yielded this (from RMAN Incremental Backups):

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First of all “the before” time is over — I’m done with my presentation. It’s been the first slot of the day — 8:30 and Cary Milsap was presenting in another hall so what chances do I have to get people in? It turned out that some people actually did show up and quite a few considering the circumstances.

I have mixed feeling on the results. The presentation started very well and I managed to wake people up at the very beginning — thanks to the “equipment” I had at hands (thanks Marco and Riyaj!). You can spot one of them on the photo (thanks for the photo Marco):

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