BlogNotes to Myself

I am pleased to announce the general availability of my usl package for R on CRAN. The package is useful for creating models according to the Universal Scalability Law, which is used to quantify the scalability of hardware or software systems. It uses measurements from an existing system to predict the throughput for different loads and can be used to learn more about the scalability limitations of the system.

This article outlines my findings of using ROWNUM with the MERGE statement in Oracle.

The pseudo column ROWNUM can be used to limit the result set to a specific number of rows. I have used this often when I had to update a lot of rows but needed to keep the size of the transaction fairly small. Systems using data replication like Materialized Views or Streams get easily out of sync when they have to cope with huge transactions.

The MERGE statement can be used to reconcile two data sets. A new row is inserted if the key is not available in the target table and it gets updated if it already exists.

Have you ever tried to use both at the same time?

Last year I published my code for a Collectd plugin to monitor OpenVZ beancounters. Here is another plugin I wrote to monitor Sendmail, the open source MTA for Unix.