Cursor Invalidation

Got a question: What will happen a running curosr got invalidated?  SQL execution will fail or invalidation is not at all possible?

There are two components for an executing cursor.  A session cached cursor (private area where row source are getting processed) in PGA and sharable execution plan (shared excution (more...)

Coherence SIG: Performance Test Driven Development

Today was speaking at Oracle Coherence SIG at London.

Below you can find slide deck from my presentation.

Coherence 101, Filters performance and indexing

In this post, I would like to share some knowledge about optimizing indexes in Oracle Coherence.

Normally you should not abuse queering features of your data grid and, hence, you are unlikely to ever need to tune indexing/queering (besides choosing which indexes to create). But sometimes, you really need to (more...)

Dtrace Explorations of Oracle Wait Events on Linux

DTrace is a great tool to measure and investigate latency for performance troubleshooting. DTrace is now coming to the Linux platform too and I would like to share a few tests I did with it. The following is meant to be a short technology exploration but hopefully it can also highlight (more...)


The TIMESTAMP WITH TIME ZONE data type that got introduced a long time ago is known for some oddities, for example Tony Hasler has a nice summary of some of them here.Here is another oddity that shows up when trying to aggregate on such a data type. Have a look at the following simple example:

create table t
rownum as id
, date '2000-01-01' + rownum - 1 as some_date
, cast(date (more...)

Java GC in Numbers – Parallel Young Collection

This is a first articles in series, where I would like to study effect of various HotSpot JVM options on duration of STW pauses associated with garbage collection.

This article will study how number of parallel threads affects duration of young collection Stop-the-World pause. HotSpot JVM has several young GC (more...)

Improving data move on EXADATA V


This is the last post in this series and I’ll not introduce anything new here, but rather just summarise the changes explained and talk a bit about the value the solution delivers to the organisation.

Let’s first review the situation we faced before implementing the changes.

The cost of writing (more...)

Improving data move on EXADATA IV

Reducing storage requirements

In the last post in this series I talked about how we sped up the move of data from operational to historical tables from around 16 hours down to just seconds. You find that post here.

The last area of concern was the amount of storage this (more...)

OraLatencyMap v1.1 and Testing with SLOB 2

Topic: OraLatencyMap v1.1 is an updated versions of a performance tool aimed at collecting and displaying Oracle wait event histogram data as latency heat maps. We will also briefly discuss an example of the usage of OraLatencyMap in the context of storage testing.

OraLatencyMap v1.1 is now available (more...)

Improving data move on EXADATA III

Moving to history tables

In the last post I talked about how we made the speed of actually writing all those log-records much faster. It has to date been so fast that no a single report of a problem has been filed. you find that post here.

Once the data (more...)

Speaking at E4 2013! … and some Exadata Patents good stuff

I’ll be co-speaking with Tyler Muth at E4  and we will be talking about Performance Visualization… some of you may already know that I’m really a big fan of Tableau and just to give you an example on what the tool can do I’ve consolidated all the different viz that (more...)

Improving data move on EXADATA II

Writing log records

The last post in this series introduced the problem briefly. You find that post here.

In this post I’ll talk about the changes made to make that writing of log records fast enough. There were 50 million records that was written. Each of them pretty much in its (more...)

Faster data move on EXADATA I


In my work among other things I tune and tweak solutions for EXADATA. Today I’ll write about a big improvement we achieved with a process that moves data from the operational tables to the ones where the history is stored.

This will not be a technical post. While I (more...)

Latency Heat Maps in SQL*plus with OraLatencyMap

Topic: This post is about the use of heat maps to investigate wait event latency in Oracle (and in particular I/O-related latency). This post also discusses a SQL*plus-based script/tool I have developed to help with this type of monitoring and performance drill-down (OraLatencyMap).

Context: Oracle (since version 11gR1) exposes (more...)

New Version Of XPLAN_ASH Tool – Video Tutorial

A new major release (version 3.0) of my XPLAN_ASH tool is available for download.

You can download the latest version here.

In addition to many changes to the way the information is presented and many other smaller changes to functionality there is one major new feature: XPLAN_ASH now also supports S-ASH, the free ASH implementation.

If you run XPLAN_ASH in a S-ASH repository owner schema, it will automatically detect that and adjust accordingly.


Direct Path Reads Again

Note: This post is about diagnosing real life scenario caused by  direct path decision change on which already covered  by Tanel Poder on his awesome Optimizer statistics-driven direct path read decision for full table scans (_direct_read_decision_statistics_driven) post
If you already read and know how to (more...)

Oracle OpenWorld Submissions – The Full Monty

Here one day before deadline, I have entered almost my entire current catalog of presentations for consideration in the Oracle OpenWorld 2013 agenda. One new for this year: “Worst Oracle ADF Project Ever” ;-)

If you would like me to speak at one of your events, the following are the presentations (more...)

ORA-00600: internal error code, arguments: [ktprhtnew6]

While recovering a database, stuck with ORA-00600 and database crashed.  We have an Oracle version 11.1 and were hitting a bug: 8310931 and fixed in 11.2.  The bug says, this problem will happen usually on high number of CPUs while doing transaction recovery.  We got 126 CPU in the DB server.

Errors in file /opt/oracle/diag/rdbms/xxxx/xxx/trace/xxx_smon_29786.trc (incident=120257):

ORA-00600: internal error code, arguments: [ktprhtnew6], [], [], [], [], [], [], [], [], [], [], []
Incident details in: /opt/oracle/diag/rdbms/xxx/xxxx/incident/incdir_120257/xxxx_smon_29786_i120257.trc
Fri Feb 22 22:49:14 2013
Trace dumping is performing id=[cdmp_20130222224914]
Fatal internal error happened while SMON was doing active  (more...)

Oracle on AIX – where’s my cpu time ?

This story begins couple of weeks ago when I was asked to look on performance problem for critical processes before go-live. There were differences between run times between different test systems and between runs with 10046 trace enabled or not.

First of all I started with tracing issue. I have checked server CPU and disk utilization using NMON (tool name is important here). There wasn’t any problem with CPU utilization – or at least this is what I was thinking at that time. Tracing was enabled with level 12 (bind and wait) and it generate 2 GB of trace file (more...)

AWR Analytics and Oracle Performance Visualization with PerfSheet4

Topic: This post describes PerfSheet4, a tool for performance analysis aimed at streamlining access and visualization of Oracle's AWR data. The tool is aimed at DBAs and Oracle performance analysts. PerfSheet4 is a spin off of previous original work by Tanel Poder, rewritten and integrated with additional functionality for AWR analysis and with important changes to the user interface.

Context: There is much information in the counters and metrics of Oracle's AWR that can be of substantial help for troubleshooting and for capacity planning. Besides the standard AWR report, time-based analysis is often very useful. However this type of access is (more...)