Linux Kernel Stack Profiling and Flame Graphs Applied to Oracle Investigations

Topic: This blog post is about kernel stack profiling and visualization with flame graphs with examples.

Stack profiling and flame graphs are very useful techniques and tools for troubleshooting and investigating workloads at the OS-level and understand which code path take most of the execution time. You can find extensive material and examples o flame graphs in Brendan Gregg's website and blog. A few additional examples of using stack tracing and flame graphs for (more...)

Little things worth knowing: automatic generation of extended statistics in 12c

When you are migrating to Oracle 12c I hope you might this post useful. I came across this feature when researching what’s new with Oracle 12c (and yes I still find lots of new ones I haven’t noticed before). This one is a bit hidden away in section 2.2.4.3 Automatic Column Group Detection of the 12c New Features Guide. And it’s a lot more complex than I first thought! In this first post (more...)

Does Linux hate Java?

Recently, I have discovered a fancy bug affecting few version of Linux kernel. Without any warnings JVM just hangs in GC pause forever. Root cause is a improper memory access in kernel code. This post by Gil Tene gives a good technical explanation with deep emotional coloring.

While this bug is not JVM specific, there are few other multithreaded processes you can find on typical Linux box.

This recent bug make me remember few other (more...)

How the log writer and foreground processes work together on commit.

(warning: this is a rather detailed technical post on the internal working of the Oracle database’s commit interactions between the committing foreground processes and the log writer)

After the Trivadis Performance days I was chatting to Jonathan Lewis. I presented my Profiling the log writer and database writer presentation, in which I state the foreground (user/server) process looks at the commit SCN in order to determine if its logbuffer contents are written to disk by (more...)

Optimizer statistics – parse time statistics aggregation

It’s getting harder and harder to find time for writing. Anyway, this post stays from a long time in my draft so, I think is time to finish and post it. That one is the last one from the optimizer statistics series. For now, of course :) After describing the horror around the way that […]

20 Things Every Computer Science Graduate Should Know Before Starting a Job

20 Things Every Computer Science Graduate Should Know Before Starting a JobYou’ve completed your Computer Science degree and have got yourself a job. Well done! Welcome to the real world! Now, there are a few things you should know before starting your first day, which I’ve listed in this article.

1 – The Days Can Be Long

Finishing a Computer Science degree will often lead you into a software development-related role. There are usually standard hours for this kind of role, which is something like 9AM (more...)

SJK – missing link in Java profiling tool chain

Sometimes it just happens. You have a bloated Java application at your hand and it does not perform well. You may have built this application yourself or just got it as it is now. It doesn't matter, thing is - you do not have a slightest idea what is wrong here.

Java ecosystem have abundance of diagnostic tools (thank for interfaces exposed at JVM itself), but they are mostly focused on some specific narrow kinds (more...)

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...)

Inserting million of time series data (rows) per second inside oracle database

This blog post is the first of a series of 4 related to time series and indexing.

According to wikipedia this is the definition of a time series:

A time series is a sequence of data points, typically consisting of successive measurements made over a time interval.

This blog post shows how we can efficiently store time series in an oracle database and how indexing strategy can have a big impact on insertion performance rate.

(more...)

Strategies for Minimising SQL Execution Plan Instability

Execution Plan Instability – What is the problem?

The Oracle Optimizer is a complex piece of software and with every release it becomes more complex.

RBO

In the beginning, the Optimizer was rule-based.

The Optimizer had a ranked list of heuristics used to optimize a query, picking the lowest ranked rule available.

This rule-based mode, whilst still in use with some internal Oracle dictionary queries, has been unsupported since version 10.1.

This means that (more...)

Visualizing Statspack “Average Active Sessions” in SQL Developer

This is the second post in my mini-series on leveraging SQL Developer Reports for DBA tasks, today with visualizing Average Active Sessions (AAS). In this article I’ll cover What AAS is and how to interpret it How to build a basic line graph in SQL Developer How to extend the graph with detailed child reports (Time […]

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...)

Visualizing Statspack Performance Data in SQL Developer

If you run Oracle Standard Edition or haven’t licenced Diagnostics Pack for Enterprise Edition, then you don’t have AWR and ASH Data available. This is when Statspack, the predecessor of AWR, comes in handy to keep a history of database performance metrics. But although Oracle still deliver Statspack with their recent DB releases (yes, even in […]

Tablespace growth history

Recently we had a tablespace space run out and ended up in an application failure.  I have questioned my DBA and he just plainly blamed the application team members who loaded large number records without a prior notice.  A convincing answer, but you can’t really fool Oracle.

Oracle introduced a new DBA_TABLESPACE_USAGE_METRICS view from 10g onwards to report the space usage with in a tablespace.  I created a new tablespace and immediately (more...)

x$bh and consistency

Oracle caches the data blocks in buffer cache in various modes depends on the block usage.  As per the Oracle documentation it can CR (Consistent mode – reads), XCUR (Current mode – updates), FREE etc.   I understand and other heard saying – whenever a block READs into memory will be in CR mode while if the block is fetching for UPDATE it will be in XCUR mode so that sessions can apply the (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...)

Binary search – is it still most optimal?

If you have a sorted collection of elements, how would you find index of specific value?
"Binary search" is likely to be your answer.
Algorithms theory is teaching us what binary search is most optimal algorithm for this task with log(N) complexity.
Well, hash table can do better, if you need to find key by exact match. In many cases, though, you have reasons to have your collection sorted, not hashed.

On my job, I'm (more...)

To N or Not to N, is SYS_OP_C2C the Question; Oracle NVARCHAR Slow?

February 8, 2015 I was recently contacted about an odd performance issue with a software product named TDM, where certain SQL statements submitted to an Oracle 9.2.x database required roughly 30 seconds to execute when a nearly instantaneous response was expected.  The person who reported the issue to me provided a sample SQL statement that […]

Bind peeking and session cached cursor

Bind peeking is a nice feature in Oracle to have many optimized plans for an SQL for various bind values.  DBAs believe that bind peeking happens during a soft parse which will identify an alternate plan. Why do I say that?

 

Hard Parse: Parsing first time, nothing exists to bind peek

 

Soft Parse :  SQL cursor is existing and executing not the first time.  Under the soft parse, bind peeking (more...)