How to use index to get NULL values

I have learned something new today and this blog post will be (primary) reminder to myself. I am sure that most Oracle DBA’s or Developers are familiar with this trick - so please skip this post if you are one of them :)

My test table will have 1000000 rows with 1000 NULL values for “OBJECT_NAME” column.

Tests are performed on 11gR1 version.

Table/column info:

select c.table_name, c.column_name, c.data_type, c.num_nulls,
t. (more...)

Consistent gets – How Many?

When you execute an SQL – why there is a difference in Consistent gets on the same set of data for same SQL.    For any SELECT query, oracle need to prepare the consistent data in the buffer cache using undo records then forward the data the requesting session as of a specific SCN.  Touching any block in buffer cache to prepare the blocks for consistent data is known as Consistent Reads.

In an (more...)

November/December Highlights

In the Oracle technical universe, it seems that the end of the calendar year is always eventful. First there’s OpenWorld: obviously significant for official announcements and insight into Oracle’s strategy. It’s also the week when many top engineers around the world meet up in San Francisco to catch up over (more...)

Instrumentation still needed

Recently I received an email with an simple content:
"It" is slow again :-)
The email explained a package to be slow.

Ok, I started with my "not enough information" reply and an email conversation began.

We are still not ready to identify the problem, but as there is no (more...)

Drill Down the I/O stack at UKOUG Tech13

It's just under a week to go before the doors open for the UKOUG Tech13 conference and the adjoining OakTable World UK 2013 sessions, so I thought I would write a very short blog post about what I will be doing there, where I'll be, and what I'm looking forward (more...)

Oracle Database 12c PRAGMA UDF and WITH clause enhancements

Here are two interesting enhancements in Oracle database 12c PL/SQL. PL/SQL subprogram defined using WITH clause of a subquery – Oracle database 12c allows PL/SQL declaration section in the WITH clause. One can define PL/SQL function or procedure into a WITH clause. Functions declared in the PL/SQL declaration section can (more...)

JVM deep dive at HighLoad++ 2013 (Moscow)

Today was speaking at HighLoad++ 2013 Moscow. I had two presentation covering deep internals of JVM. One about JIT compilation and other concerning pauseless garbage collection algorithms.

Slide decks are below (in Russian)

Performance Test Driven Development (CEE SECR 2013 Moscow)

Today I was speaking at CEE SECR 2013 at Moscow.

Below is a slide deck from presentation (in Russian)

Lessons from the Obamacare website

To no big surprise, the website went down promptly after being launched. This is the place where people sign up for “Obamacare,” and officials foolhardily insisted that everything was ready for a million visitors. It wasn’t.

Serious websites generally eschew big-bang launches because it is so hard to get (more...)

Getting Started with PyLatencyMap: Latency Heat Maps for Oracle and DTrace

Topic: this is a getting-started article for PyLatencyMap, a performance tool for real-time investigation and troubleshooting of latency data. Contains examples relevant for the Oracle RDBMS and for DTrace.

Getting started

Download the latest version of PyLatencyMap (also available on GitHub). At the time of this writing PyLatencyMap (more...)

Coherence 101 – EntryProcessor traffic amplification

Oracle Coherence data grid has a powerful tool for inplace data manipulation - EntryProcessor. Using entry processor you can get reasonable atomicity guarantees without locks or transactions (and without drastic performance fees associated).

One good example of entry processor would be built-in ConditionalPut processor, which will verify certain condition before (more...)

SJK (JVM diagnostic/troubleshoting tools) is learning new tricks.

SJK is small command line tool implementing number of helpful commands for JMV troubleshooting. Internally SJK is using same diagnostic APIs as standard JDK tools (e.g. jps, jstack, jmap, jconsole).

Recently I've made few noteworthy additions to SJK package and would like to announce them here.

Memory allocation rates (more...)

PyLatencyMap, a Performance Tool for Latency Data Visualization

Topic: this post is about PyLatencyMap, a performance-oriented tool I have written for command-line drill down of latency data, integrating various data sources (Oracle, DTrace, trace files) into a basic visualization engine.

Motivations: Understanding a performance problem is often about understanding where time is spent. Many of the systems I (more...)

oratop from MOS

This is just a pointer post to a tool which I discovered today. It is ORATOP, to monitor databases real time like top of unix flavours. It is pretty much like MOATS   (tool from Tanel Poder and Adrian Billington and RAC version by  Jagjeet Singh),   with a bit better output (more...)

Java GC in Numbers – Compressed OOPs

Compressed OOPs (OOP – ordinary object pointer) is a technique reducing size of Java object in 64 bit environments. HotSpot wiki has a good article explaining details. Downside of this technique is what address uncompressing is required before accessing memory referenced by compressed OOPs. Instruction set (e.g. x86) may (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...)

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...)