Oracle

tanelpoder's picture

New versions of LatchProf and LatchProfX for latch contention troubleshooting and tuning

The LatchProf and LatchProfX scripts allow you to be more systematic with latch contention troubleshooting and tuning. No more guesswork is needed as these scripts give you exact session IDs and in this version also SQLIDs of the troublemaking applications.

You can download the new versions here:

Example output (with SQLID info) is below:

tanelpoder's picture

Oracle Troubleshooting: How to read Oracle ERRORSTACK output?!

I have written the first article to the troubleshooting section of my new website tech.E2SN.com:

It’s about a very valuable Oracle troubleshooting tool -> ERRORSTACK trace.

I cover 4 frequently asked questions there:

  1. Reading the current executing SQL statement text from errorstack trace
  2. Reading the current executing PL/SQL package and PL/SQL source code line number from errorstack trace
  3. Reading the current bind variable values from errostack trace
  4. Identifying how much private (UGA) memory a cursor is using

You can read it here:

By the way, if you like my new website, feel free to link to it !!! ;-)

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tanelpoder's picture

Future appearances, conferences and seminars

Just to let you know where I’ll be in the near future :)

Seminars

Advanced Oracle Troubleshooting 2.0

I have rearranged and adjusted the material so it flows smoother, has even more practical tools and scripts and describes some internals even deeper ;-)

These dates are close, last chance to register ;-) Note that after these I won’t be doing an Advanced Oracle Troubleshooting class in US for a while…

Conferences

Hotsos Symposium, Dallas, TX, 8-11 March

I will deliver 2 presentations at the Hotsos Symposium 2010

  • Back to Basics: Choosing the Starting Point of Performance Tuning and Troubleshooting Wisely
  • Understanding LGWR, log file sync Waits and Commit Performance

Also, I will be the Training Day speaker after the conference (I feel quite honored about this btw ;)

  • Scripts and Tools for Oracle Troubleshooting and Advanced Performance Analysis

Note that I will show some very cool (and of course, useful) stuff at the Training Day! Some things are gonna be so cool that I almost want to sit in the audience myself! One of the things is called MOATS – the Mother Of All Tuning Scripts for example ;-)

tanelpoder's picture

Oracle Wait Event reference

Kyle Hailey has started putting together a much needed Oracle wait event reference.

You can access it here.

By the way, Oracle documentation also has a wait event reference section, it has more events, but it’s less detailed…

I have plans to go deep into some wait events and cover some less common ones in tech.E2SN too… in the future ;-)

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tanelpoder's picture

Oracle Peformance Visualization…

Coskan Gundogar and Karl Arao have written two interesting articles about Oracle performance analysis and visualization, check these out!

Coskan’s article:

Karl’s article:

Note that in March I will be releasing PerfSheet v3.0, which will have lots of improvements! ;-)

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tanelpoder's picture

Bind Variable Peeking – execution plan inefficiency

In my Beyond Oracle Wait interface article I troubleshooted a test case where an execution plan somehow went “crazy” and started burning CPU, lots of logical IOs and the query never completed.

I have uploaded the test case I used to my new website, to a section where I will upload some of my demo scripts which I show at my seminars (and people can download & test these themselves too):

http://tech.e2sn.com/oracle-seminar-demo-scripts

Basically what I do is this:

  1. I run the query with bind variable values where only a handful of rows match the filter condition. Thus Oracle picks nested loop join (and indexed access path)
  2. Then I run the same query with different bind values, where a lot of rows match the filter condition. Oracle reuses existing execution plan (with nested loops!!!). Oracle ends up looping through a lot of blocks again and again (because nested loop visits the “right” side of the join once for every row coming from the “left” side of the join).

Using nested loops over lots of rows is a sure way to kill your performance.

And an interesting thing with my script is that the problem still happens in Oracle 11.1 and 11.2 too!

Oracle 11g has Adaptive Cursor Sharing, right? This should take care of such a problem, right? Well no, adaptive bind variable peeking is a reactive technique – it only kicks in after the problem has happened!

harald's picture

How to setup a private DNS for your virtual cluster

One of the challenges I faced recently was building a virtual cluster based on Oracle 11g Release 2 on top of Oracle Enterprise Linux (OEL) running inside VMware server. Although I have an existing virtual Oracle 11g Release 1 cluster, I decided to build a new one in order to be able to teach both […]

Greg Rahn's picture

The Core Performance Fundamentals Of Oracle Data Warehousing – Partitioning

[back to Introduction] Partitioning is an essential performance feature for an Oracle data warehouse because partition elimination (or partition pruning) generally results in the elimination of a significant amount of table data to be scanned. This results in a need for less system resources and improved query performance. Someone once told me “the fastest I/O is the one that never happens.” This is precisely the reason that partitioning is a must for Oracle data warehouses – it’s a huge I/O eliminator. I frequently refer to partition elimination as the anti-index. An index is used to find a small amount data that is required; partitioning is used to eliminate vasts amounts of data that is not required. Main Uses For Partitioning I would classify the main reasons to use partitioning in your Oracle data warehouse into these four areas: Data Elimination Partition-Wise Joins Manageability (Partition Exchange Load, Local Indexes, etc.) Information Lifecycle Management (ILM) Partitioning Basics The most common partitioning design pattern found in Oracle data warehouses is to partition the fact tables by range (or interval) on the event date/time column. This allows for partition elimination of all the data not in the desired time window in queries. For example: If I have a [...]

Greg Rahn's picture

The Core Performance Fundamentals Of Oracle Data Warehousing – Table Compression

[back to Introduction] Editor’s note: This blog post does not cover Exadata Hybrid Columnar Compression. The first thing that comes to most people’s mind when database table compression is mentioned is the savings it yields in terms of disk space. While reducing the footprint of data on disk is relevant, I would argue it is the lesser of the benefits for data warehouses. Disk capacity is very cheap and generally plentiful, however, disk bandwidth (scan speed) is proportional to the number of spindles, no mater what the disk capacity and thus is more expensive. Table compression reduces the footprint on the disk drives that a given data set occupies so the amount of physical data that must be read off the disk platters is reduced when compared to the uncompressed version. For example, if 4000 GB of raw data can compress to 1000 GB, it can be read off the same disk drives 4X as fast because it is reading and transferring 1/4 of the data off the spindles (relative to the uncompressed size). Likewise, table compression allows for the database buffer cache to contain more data without having to increase the memory allocation because more rows can be stored [...]

James Morle's picture

The Oracle Wait Interface Is Useless (sometimes) – part 3a

OK, here it is, the ‘first part of the last part’, though the topics discussed in these articles will be discussed more over time in my blog and in Tanel’s. I’ve split it into two subparts, because it was just getting insanely long as single posting.

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