Posts by Alex Gorbachev

MySQL GROUP BY and DISTINCT Oddity

At the end of my last MySQL post I mentioned strange behavior with GROUP BY and DISTINCT. This MySQL “feature” could save some resources on sorts and aggregates but generally I would avoid it as this is not portable solution. Generally speaking, query output is non-deterministic — it depends on the full table scan implementation and on the physical order of rows in a table. This means that it’s actually a bug and , instead, MySQL should produce and error on those statements.

ORA-07202: sltln: invalid parameter to sltln

I’ve started to use DBCA more and I try to use its template management capabilities. It looks like templates is not the most robust feature of Database Configuration Assistant. Sometimes, there are issues when I want to reuse template. I reviewed the parameters and found that control_files is set to an empty string. Checked Metaclick and, indeed, this error is related to empty control_files parameter.

Calling Definer-Rights Procedure as SYSDBA – Security Hole?

In one of my previous posts I mentioned SYSTEM_PRIVILEGE_MAP view. Taking this thread further, I looked into another nice view – V$ENABLEDPRIVS – showing the privileges enabled for the session at the moment. It should be pretty useful if you decide to add some diagnostics into your application. You might also find it very helpful to call from PL/SQL.

Yes, More and More and Moore… but Different!

We humans are not able to process large amount of precise data. In any human–readable report, we don’t need more than ten or twenty lines of numbers. Every time we look at processes or data more complex that that, we employ simplifications — graph trends, mind–mapping, aggregations, and so on. How will we make computers process information just as humans do? Perhaps we can find the answer inside ourselves if we figure out how our minds work. We recognize images even though our brain is not capable of processing huge amounts of data in milliseconds.

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.

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