Author Archives: Bobby

I hacked together a query today that shows the overall I/O performance that a database is experiencing. The output looks like this: End snapshot time number of IOs ave IO time (ms) ave IO size (bytes) ——————- ————- —————- ——————- … Continue reading →

Oracle support says we have hit bug 13914613.  Here is what our wait events looked like in an AWR report: Top 5 Timed Foreground Events Event Waits Time(s) Avg wait (ms) % DB time Wait Class latch: shared pool 3,497 17,482 … Continue reading →

Recently I used DBMS_RESOURCE_MANAGER.calibrate_io to measure disk I/O performance using a call like this: DECLARE l_latency PLS_INTEGER; l_iops PLS_INTEGER; l_mbps PLS_INTEGER; BEGIN DBMS_RESOURCE_MANAGER.calibrate_io (num_physical_disks => 10, max_latency => 20, max_iops => l_iops, max_mbps => l_mbps, actual_latency => l_latency); DBMS_OUTPUT.put_line(‘Max IOPS = ‘ … Continue reading →

This is very cool: There are a bunch of nice computer science classes online from MIT: Free online MIT computer science classes Here is an introductory computer science class: Intro to computer science Here is a graded version of the same … Continue reading →

I dug up a simple C program that I wrote years ago to test disk performance.  I hesitated to publish it because it is rough and limited in scope and other more capable tools exist. But, I have made good … Continue reading →

In my previous post I described how I could not explain why I got better db file parallel read wait times in a test on Linux than I got running the same test on HP-UX.  I have discovered that the Linux … Continue reading →

I am still working on comparing performance between an HP-UX blade and a Linux virtual machine and I have a strange result.  I tried to come up with a simple example that would do a lot of single block I/O. … Continue reading →

I’m trying to compare two types of database servers and it looks like one has a faster CPU than the other.  But, the benchmark I have used runs a complicated variety of SQL so it is hard to really pin … Continue reading →

I need to change a view and an index on an active production system.  I’m concerned that the change will fail with a “ORA-00054: resource busy” error because I’m changing things that are in use.  I engaged in a twitter … Continue reading →

I’m trying to compare how a query runs on two different 11.2.0.3 systems.  One runs on HP-UX Itanium and one runs on 64 bit x86 Linux.  Same query, same plan, different hash value. HP-UX: SQL_ID 0kkhhb2w93cx0 ——————– update seg$ set type#=:4,blocks=:5,extents=:6,minexts=:7,maxexts=:8,exts … Continue reading →