A look into Oracle redo, part 3: log writer work cycle overview

This is the third part of a series of blogposts on how the Oracle database handles redo. The previous part talked about the memory area that stores redo strand information: https://fritshoogland.wordpress.com/2018/02/05/a-look-into-oracle-redo-part-2-the-discovery-of-the-kcrfa-structure/.

The single most important process in the Oracle database for handling redo is the log writer, which primary task is flushing the redo information other Oracle database processes put in the public redo strands to disk. Now that we have investigated the (more...)

Oracle Exadata Smart Flash Logging

What is Exadata Smart Flash Logging?

In an OLTP environment, it is crucial to have fast response times to redo log writes i.e. low latency.  When multiplexing redo logs for high availability i.e. to protect against hardware failure, redo log writes are only acknowledge when redo is written to all redo log members i.e when the slowest disk completes the write.  By this nature, whenever a disk slows down even (more...)

A look into Oracle redo, part 2: the discovery of the KCRFA structure

This is the second post in a series of blogposts on Oracle database redo internals. If you landed on this blogpost without having read the first blogpost, here is a link to the first blogpost: https://fritshoogland.wordpress.com/2018/01/29/a-look-into-oracle-redo-part-1-redo-allocation-latches/ The first blogpost contains all the versions used and a synopsis on what the purpose of this series of blogposts is.

In the first part, I showed how the principal access to the public redo strands is (more...)

A look into Oracle redo, part 1: redo allocation latches

This will be a series of posts about Oracle database redo handling. The database in use is Oracle version 12.2.0.1, with PSU 170814 applied. The operating system version is Oracle Linux Server release 7.4. In order to look into the internals of the Oracle database, I use multiple tools; very simple ones like the X$ views and oradebug, but also advanced ones, quite specifically the intel PIN tools (https://software.intel. (more...)

How to Enable Exadata Write-Back Flash Cache

Please check the following blog post “How to check if Exadata Write-Back Flash Cache is Enabled” for:

  • What is Exadata Write-Back Flash Cache?
  • What are the Performance Benefit of Exadata Write-Back Flash Cache?
  • How to check if Exadata Write-Back Flash Cache is Enabled?
  • Pre-requisites and minimum versions.

You can also get more info from My Oracle Support (MOS) note:
Exadata Write-Back Flash Cache – FAQ (Doc ID 1500257.1)
OTN Article: Oracle Exadata Database (more...)

How to check if Exadata Write-Back Flash Cache is Enabled

What is Exadata Write-Back Flash Cache?

Exadata Write-Back Flash Cache provide the ability to cache not only read I/Os but write I/O to the Exadata’s PCI flash on the storage cells.  Exadata storage software 11.2.3.2.1 or higher and Grid Infrastructure and Database software 11.2.0.3.9 or higher is required to use Exadata Write-Back Flash Cache, which is persistent across storage cell restarts.

The default since April 2017 for (more...)

How to run sundiag.sh on Exadata

Very often when creating a Support Request (SR) for an issue on an Oracle Exadata Database Machine, you’ll need to run the script “sundiag.sh“.  Which is the “Oracle Exadata Database Machine – Diagnostics Collection Tool“.

More information can be found on My Oracle Support (MOS) Note:
SRDC – EEST Sundiag (Doc ID 1683842.1)

To run “sundiag.sh“, is very simple as shown below:

[root@v1ex1dbadm01 ~]#  (more...)

Secure Erase of an Exadata System

What has to be done when the Lifecycle of an Exadata System comes to the end.

You need to do an secure erase of DB and Storage nodes.

By the way you can also secure erase the Switches and PDU, etc. but this is not described in this article.

Documentation

https://docs.oracle.com/cd/E80920_01/DBMSQ/exadata-secure-erase.htm#DBMSQ-GUID-DE6BBDF7-6BCB-412B-AD1E-E0FFEEFCC3AA

and  My Oracle Support Doc ID 2180963.1

Steps to do

I use the method via bootable USB Stick

Download Boot (more...)

Introduction to pinatrace annotate version 2: a look into latches again

This post is an introduction to pinatrace annotate version 2, which is a tool to annotate the output of the Intel Pin tools ‘pinatrace’ tool.

The pinatrace tool generates a file with every single memory access of a process. Please realise what this means: this is every single read from main memory or write to main memory from the CPU. This allows you to get an understanding what happens within a C function. This means (more...)

That demned elusive PQ slave

With apologies to Emma Orczy for stealing a line from “The Scarlet Pimpernel” … 🙂

Introduction

We ran into a strange situation at a customer site this morning. A customer asked us to kill two stuck sessions on one of their 11.2.0.4 RAC Exadata environments, normally something they have sufficient knowledge and access to be able to handle themselves. Well this time round, every time they issued an “ALTER SYSTEM KILL SESSION ‘xxx, (more...)

The hang manager

Recently I was looking in the trace directory in the diag dest of my (12.2.0.1) instance, and found some trace files which were different from the others:

$ ls | grep dia0
test_dia0_9711_base_1.trc
test_dia0_9711_base_1.trm
test_dia0_9711_lws_1.trc
test_dia0_9711_lws_1.trm
test_dia0_9711.trc
test_dia0_9711.trm

The dia0 ‘test_dia0_9711.trc’ file is fully expected. But what are these ‘..lws_1.trc’ and ‘..base_1.trc’ files? And ‘base’ is something that I understand, but (more...)

Oracle Essential Support Tools im Exadata Umfeld

Mein DOAG Vortrag zum Thema

„Oracle Support wie gehe ich vor und welche Tools setze ich im Exadata Umfeld ein“

Exadata_Oracle_Support_V1.1

Hinweis:

In der Zwischenzeit hat Oracle eine neue Version den Trace File Analyzer bereitgestellt die man dann auch einsetzen sollte. Einfach über die Doc-ID suchen.

TFA Collector – TFA with Database Support Tools Bundle (Doc ID 1513912.1)

Noch eine Anmerkung für alle die gerade PSU’s etc. eingespielt haben. Leider stellt Oracle Support (more...)

Presenting at Cloud day event of North India Chapter of AIOUG

I will be presenting a session titled “An 18 pointers guide to setting up an Exadata machine” at Cloud Day being organized by North India chapter of AIOUG. Vivek Sharma is doing multiple sessions on various cloud and performance related topics. You can register for the event here

https://www.meraevents.com/event/aioug-nic-cloud-day 

 

ksplice kernel updates and Exadata patching

If you have installed some one off ksplice fix for kernel on Exadata, remember to uninstall it before you do a kernel upgrade  eg regular Exadata patching. As such fixes are kernel version specific so they may not work with the newer version of the kernel. 

Exadata Storage Server Patching in 18.1.1 and Above

One of the cool new features that was introduced with 18.1.0.0.0 was a subtle change in the Exadata storage server patching process.  While not required, this new functionality removes the need to use patchmgr to drive Exadata storage server patches.  In Juan Loaiza’s Open World session on new Exadata features, this slide jumped out to me:

While this slide may look like marketing fluff, this new feature turns out (more...)

Oracle 12.1 big table caching IO code path

Recently I was triggered about the ‘automatic big table caching’ feature introduced in Oracle version 12.1.0.2 with Roger Macnicol’s blogpost about Oracle database IO and caching or not caching (https://blogs.oracle.com/smartscan-deep-dive/when-bloggers-get-it-wrong-part-1 https://blogs.oracle.com/smartscan-deep-dive/when-bloggers-get-it-wrong-part-2). If you want to read something about the feature in general, search for the feature name, you’ll find several blogposts about it.

If you are not familiar with automatic big table caching, it’s a feature (more...)

Exadata Flash Cache enabled for Write Back

During Tests for an Migration of a major customer application we saw in our AWR reports that most of the jobs are very write intensive. This was the point where we would like to test what happens when we change the Flash Cache Mode from Write Through to Write Back.

What are the main benefits of Write Back mode:

  • it improves the write intensive operations while writing to flash cache is faster than writing to (more...)

Oracle C functions annotations

Warning! This is a post about Oracle database internals for internals lovers and researchers. For normal, functional administration, this post serves no function. The post shows a little tool I created which consists of a small database I compiled with Oracle database C function names and a script to query it. The reason that keeping such a database makes sense in the first place, is because the Oracle C functions for the Oracle database are (more...)

Thoughts About the Exadata X7-2 Launch

Last week’s Oracle Open World conference included many different announcements – one that impacts my work was the release of a new generation of Exadata machines – this time, the X7-2. If you’ve followed Exadata development over the years, there has been a typical set of features that come in with each release:

  • Increase in CPU core count
  • Increase in disk storage (typically 2x)
  • Increase in flash storage (typically 2x)
  • New software features

The screenshot (more...)

ODC Appreciation Day : Oracle Exadata Database Machine

Those that know me well, will know about my “appreciation” of the “Oracle Exadata Database Machine“, more commonly known as “Exadata🙂

So this will be my contribution to ODC Appreciation Day formally known as OTN Appreciation Day, a great initiative by Tim Hall aka Oracle-Base.com.

You can see a summary of last year’s blog post here:
OTN Appreciation Day : Summary

The very first Exadata, was the (more...)