Posts by Alex Gorbachev

MySQL Can’t Use Index With Uncorrelated IN Subquery

Today is the first time I had to look at MySQL performance. Tiny database as web application back-end was having significant performance issues with spikes of CPU workload. After identifying problematic queries, I found a pile of statements using IN subqueries. I asked around and our MySQL experts assured me that this is one of the minor and not so disturbing issues, in fact. I can’t imagine what those disturbing issue are. I guess Oracle XE does have some advantages over MySQL for small installations.

Welcome Doug!

Doug Burns is finally here in Ottawa. You must see his smile in the airport – somehow he managed to read my comment and already expected me while I thought it would be surprise.

Twitter, Pythian Style… also Oracle’s SYSTEM_PRIVILEGE_MAP

To the subject at hand (psst, there will be some technical stuff in the end)… A few days ago I came across Twitter. I liked that idea very much and even tried it for one evening. I don’t think Twitter fits my lifestyle, but I recognized a very familiar concept. Indeed, it reminds me of one feature of our Pythian Support Track. Time for a bit of technical stuff…since we are mostly talking about databases on this blog, here is a view in Oracle I found very useful one day: SYSTEM_PRIVILEGE_MAP.

“change tracking state change latch”

In my UKOUG 06 presentation on block change tracking internals I assumed that “change tracking state change latch” is, probably, used by DBWR and CTWR to protect access to a buffer area in shared pool. I wanted to verify it and tried to trace this latch.

Which Risks Are You Protected From?

I worked on one site for a while and during 2.5 years it didn’t face a single media corruption of Oracle datafiles. But one day, my fellow DBA (who is usually extremely cautious and reviews his actions at least twice) overwrote a controlfile with some crap. Even the fact that controlfiles were on raw devices didn’t prevent this disaster from happening.

A Good DBA’s Peripheral Vision

I believe that a good DBA should have well developed “peripheral vision”. It helps everywhere — troubleshooting production issues or performance problems, database/application design, system architecture, reading documentation, etc. I also notice that a newbie DBA with good peripheral vision catches up much faster than a strictly focused person.

MySQL and PostreSQL on Solaris 10

First of all, there is now FREE Solaris 10 media kit available to order by mail if you’re not fancy downloading several GB. By the way, it also includes Sun Studio (anyone using it?). Second, I found a cool article on Solaris BigAdmin portal – Deployment Guide for an Open Source Stack on the Solaris 10 OS also available as PDF.

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