Heat Map Visualization of Latency Histograms for NetApp C-Mode

Topic: This post is about collecting and visualizing I/O latency histograms for NetApp filers in C-mode.

Motivations: The drill down of I/O latency is an important technique for troubleshooting and benchmarking storage. Average latency values can hide details of what is happening on the storage. Think for example of storage systems with flash and spindles, each serving I/O at different latency. Moreover averaging the measured values over time can hide details in case of varying (more...)

Event Histogram Metric and Oracle 12c

Topic: event histogram metric, a script and some related comments on collecting and displaying wait event latency histograms for Oracle performance troubleshooting.

Why: Latency histograms (and by extension wait event histograms) provide very useful information when troubleshooting performance for systems exhibiting response time with multi-mode distribution. In such cases average wait values are often not sufficient to understand the behavior of the system under study and histograms provide a finer level of details. A (more...)

Heat Map Visualization for SystemTap

Topic: PyLatencyMap v1.2 and how it can be used to produce heat map visualization of SystemTap histograms.

Introduction: When studying storage performance, the latency drill down is a very important data source. Measuring the average I/O latency is often not enough, latency histograms are proven to more suitable for investigating modern storage systems. This is because for many storage systems the response time has multiple modes: think for example of the common case of storage (more...)

Latest updates to PerfSheet4, a tool for Oracle AWR data mining and visualization

Topic: This post is about the latest updates to PerfSheet4 v3.7 (February 2015). PerfSheet4 is a tool aimed at DBAs and Oracle performance analysts. It provides a simplified interface to extract and visualize AWR time series data using Excel pivot charts.

Why PerfSheet4: PerfSheet4 is aimed at querying and displaying time-series data from AWR repository tables. This is very a rich source of information to analyze database workloads and trends in the context of performance analysis or (more...)

Talks at UKOUG TECH 2014 with CERN speakers

This is a short blog post with a list of the talks at the UKOUG TECH 2014 conference in Liverpool with CERN speakers. Come and say hi, we hope to see many of you there!

(*) slides can be downloaded from: http://cern.ch/canali

Life of an Oracle I/O: tracing logical and physical I/O with systemtap

Topic: This post is about tracing logical and physical reads in Oracle using systemtap. You will find a few examples illustrating the main mechanisms used by Oracle to do physical and logical I/O and you will learn how to build systemtap scripts to further explore and troubleshoot Oracle I/O.

Introduction: Performing input/output to and from the storage media, i.e. physical I/O, is one of the critical tasks underlying all database engines. When accessing data (more...)

SystemTap into Oracle for Fun and Profit

Topic: This post is about using SystemTap for investigating and troubleshooting Oracle RDBMS. In particular you will learn how to probe Oracle processes and their userspace functions. These techniques aim to be useful as well as fun to learn for those keen into peeking under the hood of the technology and improve their effectiveness in troubleshooting and performance investigations.


Userspace probing is a very powerful technique that can be used to complement the available (more...)

Scaling up Cardinality Estimates in

Topic: Counting the number of distinct values (NDV) for a table column has important applications in the database domain, ranging from query optimization to optimizing reports for large data warehouses. However the legacy SQL method of using SELECT COUNT (DISTINCT <COL>) can be very slow. This is a well known problem and Oracle provides a new function APPROX_COUNT_DISTINCT implemented with a new-generation algorithm to address this issue by providing (more...)