If you use ASM on a regular basis, you may find that knowledge of the internals
can be very useful for advanced troubleshooting
and in general to acquire familiarity
with the technology. In particular this is even more relevant when using ASM capabilities for data redundancy/mirroring (i.e. when deploying disk groups with normal or high redundancy).
I have first started investigating this topic when deploying 10g RAC databases in 2005. From time to time (more...)
This post is about investigating the Oracle Optimizer using stack sampling and flame graphs. We will see how the complexity of the Optimizer has increased over the years and in particular with the introduction of cost-based optimization and more recently with 12c adaptive optimization.Context and goal:
Stack sampling and visualization with flame graphs are powerful techniques to probe the activity of OS processes and in particular for advanced investigations and troubleshooting of Oracle (more...)
This post is a hands-on introduction to using on-CPU Flame Graphs for investigating Oracle workloads. This technique is about collecting and analyzing sampled stack trace data to analyze and troubleshoot Oracle processes at the OS level (in particular applied to Linux).Motivations:
The techniques and tools described here can be used for performance investigations
to complement wait-event based information gathered from the Oracle engine, such as information available with ASH and sql monitoring. They (more...)
This blog entry is about investigating Oracle's DBMS_RESOURCE_MANAGER.CALIBRATE_IOSpoiler:
If you have reached this article in search of a tool for quantitative analysis of storage performance and in particular for measuring random read I/O in Oracle, I'd rather advise you to use tools that allow generating test workloads in a controlled manner, in a way that can be understood and measured and in particular with latency details together with IOPS measurements. For example (more...)
This post introduces the latest changes to OraLatencyMap and PyLatencyMap, two custom tools for collecting and displaying Oracle wait event latency details using heatmaps.OraLatencyMap
is a SQL*Plus tool, with a core written in PL/SQL, aimed at studying Oracle random I/O by displaying the latency drill-down of the wait event 'db file sequential read' using heatmaps. The tool can also be used to collect and display event latency histograms for any other Oracle wait (more...)
This post is about a performance analysis technique based on high frequency sampling of wait event history data in Oracle. Two scripts are provided for performing this type of analysis and two example cases are discussed applied to the study random read latency and read workload characterization.
In the context of performance analysis, for example for a study of I/O response time, I want to analyze the flow of all wait events
This post is about exploring the mechanisms used by Oracle Clusterware 184.108.40.206 to restrict remote service registration, i.e. the 12c new feature "Restricting Service Registration for Oracle RAC Deployments"Why is this useful?
This improvement of 12c clusterware and listeners over the 11.2 version is useful mainly for security purposes, for example as a measure against TNS poisoning attacks (see also CVE-2012-1675
), and it is particularly relevant for (more...)
This post describes a few tips and techniques on how to recover ASM files from a dropped disk group and an example of how to 'undrop' an ASM disk groupContext:
This research stems from a recent case I have investigated where the data disk group of a test (more...)
I am looking forward to participating again to the UKOUG annual conference
. This year I will present together with my colleague Marcin Blaszczyk on two topics that are follow-up of articles in this blog.
The first talk is: Storage Latency for Oracle DBAs
. A presentation about a performance tuning techniques for (more...)
this article is about a tip for Oracle 11.2 and higher on how to handle DST change when querying directly the AWR repository. In addition a few comments on Perfsheet4, a tool to extract and plot AWR data in Excel.Introduction:
Statspack and more recently AWR reports