OK, so while trying to understand Oracle’s redo latching mechanisms (we have been experiencing a nightmare with log file sync since switching to a new DMX subsystem), I found that java 1.5 has a new Lock class. How cool is…
Month: April 2009
Standby created without a standby controlfile?!!
Today, a junior DBA created a standby database by copying the controlfile to another host, restoring the 4TB database it serves, and recovering all available logs via RMAN. Sounds good, right? Well, it was until we went into SQL*PLUS and…
Read only tablespace requires no outstanding transactions…anywhere…
Nice little gotcha I received yesterday morning. Our intention is to rebuild two large tables from range partitioning to hash partitioning on another server. One of the datafiles for the tablespace that houses one of the tables in question is…
Oracle function to calculate wait event correlation
Cool little function to provide statistical correlation between two events. This helped us to identify performance drivers in our database. Statistically, anything above 60 is considered “statistically significant”, or correlated. If one goes up, so does the other. create or…
Statistical functions with java
Below is a simple set of classes for performing your own statistical analysis. As noted, they are simple (no multiple regression analysis, etc.) class myStats { double standardDeviation (double[] array) { double[] arr = new double[array.length]; double av = average(array);…
Control file writes when updating???
I had never seen this before, but while testing a migration strategy for a large table with XMLTYPE’s, almost half our wait time was spent on control file sequential read and control file parallel write waits. Each of these occurred…
Oracle regular expressions
A recent question on CDOS was regarding how to have only one space at the end of a CSV output row. Below was my response… SQL> create table t1110(c varchar2(10)) 2 / Table created. SQL> insert into t1110 values(‘1’) 2…
C callouts from MySQL
While I was trying to find a way to use the statistical functions built into MySQL for performance measurement, I discovered the ability to create user defined functions that use C callouts from within the database. I knew you could…
Multicollinearity
The predictors should not correlate. In the stepwise selection one variable might take the prediction of the another variable into the model and the second variable will not be taken in to the model. The variables might get also inconsistent…
Does correlation help at all?
While studying how we can use statistics to better understand the performance of our applications, I came upon the concept of kurtosis. What this essentially means is that any given distribution is not normal if its kurtosis is very high…OK,…