Sequences in Oracle 10g RAC

I got a call from a developer who had a table with a primary key populated by a sequence, a timestamp column with the current date and some other columns. He had a specific set of data that, when ordered by the primary key had out of order timestamps. He was puzzled how this could be. We changed the sequence to “ordered” and increased the cache to 1000. Now selecting on either node gets the next number as he expected. I warned him that there would be some performance implications due to cluster synchronization. Him being a responsive developer, asked me what the impact would be, so I tested it out.

Announcing Pythian Goodies

I’ve been wondering for a while now how best to transfer knowledge efficiently and in a fun way. Presentations are good, but they require a lot of effort in preparation and research, and they are not as interactive as they could be when the group is smaller. To answer some of these issues, I would like to introduce you to Pythian Goodies. What is a Pythian Goody session you ask? Find out here.


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.

Scaling MySpace: Treading Water in a Tsunami

Those of you that that enjoyed my post on Stability, Agility, Scalability and Cost: The eBay example are sure to like this technical interview of the desperate efforts to stay only a bit behind the traffic demands at MySpace, written by David Carr at Baseline Magazine. A worthy read for those of you interested in the lofty heights of database scaling, where we pack oxygen and have to make some choices and compromises along the way.

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